Zinc

Definition

Purpose

Description

Precautions

Interactions

Aftercare

Complications

Parental concerns

Resources

Definition

Zinc is a trace element considered a micronutrient, meaning a nutrient needed in very small amounts. It is found in almost every living cell. The significance of zinc in human nutrition and public health was recognized relatively recently (1961) and it is now considered to have a wide range of essential biological roles in maintaining life and health.

Purpose

Zinc is considered essential to maintain health. It is required for the activity of numerous metalloen-zymes involved in metabolism , it maintains the immune system that protects the body against disease, and also supports normal growth and development during pregnancy, childhood, and adolescence. It plays three crucial roles:

• Catalytic role: Enzymes are proteins that are vitally important for speeding up the biochemical reactions (catalysis) of cells and organisms and nearly 200 different ones depend on zinc. Zinc-dependent enzymes can be found in all known classes of enzymes.
• Structural role: Zinc also maintains the structure of proteins and cell membranes. A finger-like structure, called a zinc finger motif, strengthens the structure of several important proteins and enzymes. For instance, that of the antioxidant copper-zinc superoxide dismutase enzyme. Copper is required for the catalytic activity of the enzyme, but zinc plays a critical structural role. Zinc also affects the structure and function of cell membranes, which become more likely to be damaged by harmful oxidative species (oxidative stress) with zinc loss.
• Regulatory role: Zinc finger proteins are also involved in the regulation of gene expression by binding to DNA and influencing the copying of specific genes. Zinc also plays a role in the regulation of cell signaling

Zinc

(Illustration by GGS Information Services/Thomson Gale.)

and influences the release of hormones and the transmission of nerve impulses.

Additionally, zinc has the following functions:

• It is required for vision, taste, and smell.
• It maintains healthy a healthy connective tissue in skin.
• It helps tissue repair after burns and wound healing.
• It is needed for bone growth.
• It promotes the production of healthy white blood cells and antibodies, important components of the body's immune system.
• It is involved in the metabolism of carbohydrates, proteins and phosphorus.
• It is involved in the production of insulin in the pancreas.

Recent research reports indicate that zinc has been found to play a role in cell death (apoptosis) with implications for growth and development, as well as a number of chronic diseases. Zinc is also actively taken up by synaptic vesicles that store the neurotransmitters released by nerve cells, suggesting a new role in neuronal activity and memory.

Description

Zinc is found in the body in a form bound to proteins within cells, especially in the nucleus, and cell membranes. The adult body contains about 1.5-2.5 g of zinc bound to various proteins. They occur in specialized areas of the brain that produce the chemical substances that can send messages from one nerve cell to another (neurotransmitters). Zinc is also found in the pancreas, adrenal gland, bones, liver, prostate and in the reproductive organs. Most of the zinc (75-88%) in blood is found in a red blood cell metalloenzyme called carbonic anhydrase. In the plasma, zinc is bound to proteins such as alpha-2-macroglobulin, albumin, transferrin and ceruloplasmin.

Zinc is found in a wide variety of foods. Oysters are the richest zinc source per serving, but since they are not consumed regularly in the American diet, red meat and poultry provide the majority of dietary zinc. Other good zinc sources include beans, nuts, certain seafood, whole grains, fortified breakfast cereals, and dairy products. Zinc absorption is more efficient from a diet high in animal protein than a diet rich in plant proteins. Phy-tates, which are found in whole grain breads, cereals, legumes and other products, are believed to decrease zinc absorption. Some good food sources of zinc include (per 1oz-serving or as indicated):

• oysters, 6 medium (16 mg)
• beef shank, lean (3 mg)
• beef chuck, lean (2.7 mg)
• beef tenderloin, lean (1.6 mg)
• pork shoulder, lean (1.4 mg)
• beef, eye of round, lean (1.3 mg)
• pork tenderloin, lean (0.8 mg)
• chicken leg, meat only (0.9 mg)
• chicken breast, meat only (0.9 mg)
• yogurt, plain, low fat (2.2 mg per cup)
• baked beans, canned with pork (0.6 mg)
• cashews, dry roasted, no salt (1.6 mg)
• pecans, dry roasted, no salt (1.4 mg)
• chickpeas, canned (2.6 mg per cup)
• mixed nuts, dry roasted, no salt (1.1 mg)

KEY TERMS

Acrodermatitis enteropathica— A genetic disorder resulting from the impaired uptake and transport of zinc in the body.

Albumin— Water-soluble proteins that can be coagulated by heat and are found in egg white, blood serum, milk.

Amino acid— Organic (carbon-containing) molecules that serve as the building blocks of proteins.

Antibody— A protein produced by the body's immune system that recognizes and helps fight infections and other foreign substances in the body.

Antioxidant enzyme— An enzyme that can counteract the damaging effects of oxygen in tissues.

Ceruloplasmin— A blue copper containing dehydrogenase protein found in serum that is apparently involved in copper detoxification and storage.

Chelating agent— An organic compound in which atoms form more than one bond with metals in solution.

Cofactor— A compound that is essential for the activity of an enzyme.

DNA— The material inside the nucleus of cells that carries genetic information. The scientific name for DNA is deoxyribonucleic acid.

Enzyme— Enzymes are proteins and vitally important to the regulation of the chemistry of cells and organisms.

Gene expression— The process by which the coded information of a gene is translated into the proteins or RNA present and operating in the cell.

High-density lipoprotein (HDL)— HDL is called the “good cholesterol”because it helps remove fat from the body by binding with it in the bloodstream and carrying it back to the liver for excretion in the bile and disposal.

L-cysteine— A sulfur-containing amino acid produced by enzymatic or acid hydrolysis of proteins. Supplements are used as antioxidant.

L-histidine— An essential amino acid, C6H9N3O2, important for the growth and repair of tissues.

Lipoproteins— Proteins present in blood plasma. The five major families are: chylomicrons, very low-density lipoproteins (VLDL), intermediate-density lipoproteins (IDL), low-density lipoproteins (LDL), and high-density lipoproteins (HDL).

Metalloenzyme— An enzyme that contains a tightly bound metal ion, such as cobalt, copper, iron or zinc.

Oxidative stress— Accumulation in the body of destructive molecules such as free radicals that can lead to cell death.

Plasma— The liquid part of the blood and lymphatic fluid. Plasma is 92% water, 7% protein and 1% minerals.

RNA— A chemical similar to DNA from which proteins are made. Unlike DNA, RNA can leave the nucleus of the cell.

Short bowel syndrome— Problems related to absorbing nutrients after removal of part of the small intestine.

Sickle cell anemia— Genetic disorder in which red blood cells take on an unusual shape, leading to other problems with the blood.

Synaptic vesicles— Also called neurotransmitter vesicles, these pouches store the various neurotrans-mitters that are released by nerve cells into the synaptic cleft of a synapse.

Trace minerals— Minerals needed by the body in small amounts. They include: selenium, iron, zinc, copper, manganese, molybdenum, chromium, arsenic, germanium, lithium, rubidium, tin.

Transferrin— A protein synthesized in the liver that transports iron in the blood to red blood cells.

Ulcerative colitis— Inflammation of the inner lining of the colon, characterized by open sores that appear in its mucous membrane.

• walnuts, black, dried (1.0 mg)
• almonds, dry roasted, no salt (1.0 mg)
• milk (1.8 mg per cup)
• cheese, Swiss (1.1 mg)
• cheese, Cheddar (0.9 mg)
• cheese, Mozzarella, part skim (0.9 mg)
• beans, kidney, California red (1.6 mg per cup)
• peas, green, frozen (1.6 mg per cup)
• oatmeal, instant, low salt (0.8 mg per packet)
• flounder, sole (0.2 mg)

The Recommended Dietary Allowance (RDA) for zinc is:

• infants: (0-6 months): 3 mg
• infants: (7-12 months): 3 mg
• children (1-3 y): 3 mg
• children (4-8 y): 5 mg
• children (9-13 y): 8 mg
• adolescents (14-18): males, 11 mg, females, 9 mg
• adults: males, 11 mg, females, 8 mg
• pregnancy: 13 mg
• lactation: 14 mg

Zinc in nutritional supplements is available as zinc gluconate, zinc oxide, zinc aspartate, zinc picolinate, zinc citrate, zinc monomethionine and zinc histidine. They are distributed as stand-alone or combination products as tablets, capsules or liquids.

Precautions

Zinc deficiency most often occurs when zinc intake is inadequate or poorly absorbed and it can have serious health consequences. Moderate to severe zinc deficiency is rare in the United States. However, it is highly prevalent in developing countries. The symptoms of severe deficiency include the slowing or cessation of growth and development, delayed sexual maturation, skin rashes, chronic and severe diarrhea, immune system deficiencies, poor wound healing, decreased appetite, impaired taste sensation, night blindness, swelling and clouding of the corneas, and behavioral disorders. These symptoms were first accurately described when a genetic disorder called acrodermatitis enter-opathica was linked to zinc deficiency. Although mild dietary zinc deficiency is unlikely to cause such severe symptoms, it is known to contribute to several health problems, especially in young children. Zinc deficiency leads to impaired physical and neuropsychological development, and to an increased risk of life-threatening infections in young children. Individuals at risk of zinc deficiency include:

• infants and children
• pregnant and breastfeeding women, especially teenagers
• patients receiving intravenous feeding
• malnourished individuals, including those with anorexia nervosa
• people with severe or persistent diarrhea
• people with malabsorption syndromes, including celiac disease and short bowel syndrome
• people with inflammatory bowel disease, including Crohn's disease and ulcerative colitis
• people with alcoholic liver disease
• people with sickle cell anemia
• elderly people
• strict vegetarians whose major food staples are grains and legumes because the high levels of phytic acid in these foods lower the absorption of zinc

Fortified foods include many types of breakfast cereals that make it easier to consume the RDA for zinc. However, they also make it easier to consume too much zinc, especially if zinc supplements are also taken. Anyone considering zinc supplementation should accordingly first consider whether their needs could be met by dietary zinc sources and from fortified foods. Intakes between 150 and 450 mg of zinc per day lead to copper deficiency, impaired iron function, reduced immune function, and reduced levels of high-density lipoproteins, the “good cholesterol”. A few isolated cases of acute zinc toxicity have been reported for food or beverages contaminated with zinc present in galvanized containers. Single doses of 225-450 mg of zinc are known to induce vomiting. Milder gastrointestinal distress has been reported at doses of 50-150 mg/day of supplemental zinc.

Interactions

The simultaneous administration of zinc supplements and certain antibiotics, such as tetracyclines and quinolones, may decrease absorption of the antibiotic with potential reduction of their action. To prevent this interaction, it is recommended to take the zinc supplements and antibiotics at least two hours apart. Metal chelating agents like penicillamine, used to treat copper overload in Wilson's disease, and diethylene-triamine pentaacetate (DTPA), used to treat iron overload, can lead to severe zinc deficiency. Anticonvulsant drugs, such as sodium valproate, may also cause zinc deficiency. The prolonged use of diuretics may increase urinary zinc excretion, resulting in increased zinc losses. A medication used to treat tuberculosis, ethambutol, has been shown to increase zinc loss in rats.

Interactions of zinc taken with other supplements are as follows:

• Calcium: May lower zinc absorption in postmenopausal women.
• Iron: May reduce the absorption of both iron and zinc.
• Phosphate salts: May lower the absorption of zinc.
• L-cysteine: May increase the absorption of zinc.
• L-histidine: May also enhance the absorption of zinc.

Aftercare

In the case of zinc deficiency, oral zinc therapy usually results in the complete disappearance of symptoms, but it must be maintained indefinitely in individuals with the acrodermatitis enteropathica.

Excessive intake can be corrected by bringing levels back to the RDA values.

Complications

It has been estimated that 82% of pregnant women worldwide are likely to have inadequate zinc intakes. Zinc deficiency has been associated with a number of pregnancy complications, including low birth weight, premature delivery, and labor and delivery complications.

The adverse effects of zinc deficiency on immune system function are also likely to increase complications in children that have infectious diarrhea. Persistent diarrhea contributes to zinc deficiency and malnutrition. Recent research has shown that zinc deficiency may also increase the harmful effects of toxins produced by diarrhea-causing bacteria like E. coli. Zinc supplementation in combination with drinking plenty of liquids has also been shown to significantly reduce the duration and severity of childhood diarrhea.

Parental concerns

Significant delays in growth and weight gain, known as growth retardation or failure to thrive, are common symptoms of mild zinc deficiency in children. But since many of the symptoms associated with zinc deficiency are general and also observed with other medical conditions, parents should not assume that they are due to a zinc deficiency. It is important to consult with a health care professional concerning medical symptoms so that appropriate care can be given.

Resources

BOOKS

Bogden, J., ed. Clinical Nutrition of the Essential Trace Elements and Minerals (Nutrition and Health). Totowa, NJ: Humana Press, 2000.

Challem, J., Brown, L. User’s Guide to Vitamins & Minerals. Laguna Beach, CA: Basic Health Publications, 2002.

Garrison, R., Somer, E. The Nutrition Desk Reference. New York, NY: McGraw–Hill, 1998.

Griffith, H. W. Minerals, Supplements & Vitamins: The Essential Guide. New York, NY: Perseus Books Group, 2000.

Larson Duyff, R. ADA Complete Food and Nutrition Guide, 3rd ed. Chicago, IL: American Dietetic Association, 2006.

Newstrom, H. Nutrients Catalog: Vitamins, Minerals, Amino Acids, Macronutrients—Beneficials Use, Helpers, Inhibitors, Food Sources, Intake Recommendations. Jefferson, NC: McFarland & Company, 1993.

Quesnell, W. R. Minerals: The Essential Link to Health. Long Island, NY: Skills Unlimited Press, 2000.

Wapnir, R. A. Protein Nutrition and Mineral Absorption. Boca Raton, FL: CRC Press, 1990.

ORGANIZATIONS

American Dietetic Association (ADA). 120 South Riverside Plaza, Suite 2000, Chicago, IL 60606-6995. 1-800/877-1600. <http://www.eatright.org.>

American Society for Nutrition (ASN). 9650 Rockville Pike, Bethesda, MD 20814. (301) 634-7050. <http://www.nutrition.org>

Office of Dietary Supplements, National Institutes of Health. National Institutes of Health, Bethesda, Maryland 20892 USA. <http://ods.od.nih.gov>.

U.S. Department of Agriculture, Food and Nutrition Information Center. National Agricultural Library,10301 Baltimore Avenue, Room 105, Beltsville, MD 20705. (301) 504-5414. <http://www.nal.usda.gov>.

Monique Laberge, Ph.D.

Zinc

Definition

Zinc is a trace element considered a micronutrient, meaning a nutrient needed in very small amounts. It is found in almost every living cell. The significance of zinc in human nutrition and public health was recognized relatively recently (1961) and it is now considered to have a wide range of essential biological roles in maintaining life and health.

Purpose

Zinc is considered essential to maintain health. It is required for the activity of numerous metalloenzymes involved in metabolism, it maintains the immune system that protects the body against disease, and also supports normal growth and development during pregnancy, childhood, and adolescence. It plays three crucial roles:

• Catalytic role: Enzymes are proteins that are vitally important for speeding up the biochemical reactions (catalysis) of cells and organisms and nearly 200 different ones depend on zinc. Zinc-dependent enzymes can be found in all known classes of enzymes.
• Structural role: Zinc also maintains the structure of proteins and cell membranes. A finger-like structure, called a zinc finger motif, strengthens the structure of several important proteins and enzymes. For instance, that of the antioxidant copper-zinc superoxide dismutase enzyme. Copper is required for the catalytic activity of the enzyme, but zinc plays a critical structural role. Zinc also affects the structure and function of cell membranes, which become more likely to be damaged by harmful oxidative species (oxidative stress) with zinc loss.
• Regulatory role: Zinc finger proteins are also involved in the regulation of gene expression by binding to DNA and influencing the copying of specific genes. Zinc also plays a role in the regulation of cell signaling and influences the release of hormones and the transmission of nerve impulses.

Additionally, zinc has the following functions:

• It is required for vision, taste, and smell.
• It maintains healthy a healthy connective tissue in skin.
• It helps tissue repair after burns and wound healing.
• It is needed for bone growth.
• It promotes the production of healthy white blood cells and antibodies, important components of the body's immune system.
• It is involved in the metabolism of carbohydrates, proteins and phosphorus.
• It is involved in the production of insulin in the pancreas.

Recent research reports indicate that zinc has been found to play a role in cell death (apoptosis) with implications for growth and development, as well as a number of chronic diseases. Zinc is also actively taken up by synaptic vesicles that store the neurotransmitters released by nerve cells, suggesting a new role in neuronal activity and memory.

Description

Zinc is found in the body in a form bound to proteins within cells, especially in the nucleus, and cell membranes. The adult body contains about 1.5–2.5 g of zinc bound to various proteins. They occur in specialized areas of the brain that produce the chemical substances that can send messages from one nerve cell to another (neurotransmitters). Zinc is also found in the pancreas, adrenal gland, bones, liver, prostate and in the reproductive organs. Most of the zinc (75–88%) in blood is found in a red blood cell metalloenzyme called carbonic anhydrase. In the plasma, zinc is bound to proteins such as alpha-2-macroglobulin, albumin, transferrin and ceruloplasmin.

Zinc is found in a wide variety of foods. Oysters are the richest zinc source per serving, but since they are not consumed regularly in the American diet , red meat and poultry provide the majority of dietary zinc. Other good zinc sources include beans, nuts, certain seafood, whole grains, fortified breakfast cereals, and dairy products. Zinc absorption is more efficient from a diet high in animal protein than a diet rich in plant proteins. Phytates, which are found in whole grain breads, cereals, legumes and other products, are believed to decrease zinc absorption. Some good food sources of zinc include (per 1oz-serving or as indicated):

• oysters, 6 medium (16 mg)
• beef shank, lean (3 mg)
• beef chuck, lean (2.7 mg)
• beef tenderloin, lean (1.6 mg)
• pork shoulder, lean (1.4 mg)
• beef, eye of round, lean (1.3 mg)
• pork tenderloin, lean (0.8 mg)
• chicken leg, meat only (0.9 mg)
• chicken breast, meat only (0.9 mg)
• yogurt, plain, low fat (2.2 mg per cup)
• baked beans, canned with pork (0.6 mg)
• cashews, dry roasted, no salt (1.6 mg)
• pecans, dry roasted, no salt (1.4 mg)
• chickpeas, canned (2.6 mg per cup)
• mixed nuts, dry roasted, no salt (1.1 mg)
• walnuts, black, dried (1.0 mg)
• almonds, dry roasted, no salt (1.0 mg)
• milk (1.8 mg per cup)
• cheese, Swiss (1.1 mg)
• cheese, Cheddar (0.9 mg)
• cheese, Mozzarella, part skim (0.9 mg)
• beans, kidney, California red (1.6 mg per cup)
• peas, green, frozen (1.6 mg per cup)
• oatmeal, instant, low salt (0.8 mg per packet)
• flounder, sole (0.2 mg)

KEY TERMS

Acrodermatitis enteropathica —A genetic disorder resulting from the impaired uptake and transport of zinc in the body.

Albumin —Water-soluble proteins that can be coagulated by heat and are found in egg white, blood serum, milk.

Amino acid —Organic (carbon-containing) molecules that serve as the building blocks of proteins.

Antibody —A protein produced by the body's immune system that recognizes and helps fight infections and other foreign substances in the body.

Antioxidant enzyme —An enzyme that can counteract the damaging effects of oxygen in tissues.

Ceruloplasmin —A blue copper containing dehydrogenase protein found in serum that is apparently involved in copper detoxification and storage.

Chelating agent —An organic compound in which atoms form more than one bond with metals in solution.

Cofactor —A compound that is essential for the activity of an enzyme.

DNA —The material inside the nucleus of cells that carries genetic information. The scientific name for DNA is deoxyribonucleic acid.

Enzyme —Enzymes are proteins and vitally important to the regulation of the chemistry of cells and organisms.

Gene expression —The process by which the coded information of a gene is translated into the proteins or RNA present and operating in the cell.

High-density lipoprotein (HDL) —HDL is called the “good cholesterol” because it helps remove fat from the body by binding with it in the bloodstream and carrying it back to the liver for excretion in the bile and disposal.

L-cysteine —A sulfur—containing amino acid produced by enzymatic or acid hydrolysis of proteins. Supplements are used as antioxidant.

L-histidine —An essential amino acid, C6H9N3O2, important for the growth and repair of tissues.

Lipoproteins —Proteins present in blood plasma. The five major families are: chylomicrons, very low-density lipoproteins (VLDL), intermediate-density lipoproteins (IDL), low-density lipoproteins (LDL), and high-density lipoproteins (HDL).

Metalloenzyme —An enzyme that contains a tightly bound metal ion, such as cobalt, copper, iron or zinc.

Oxidative stress —Accumulation in the body of destructive molecules such as free radicals that can lead to cell death.

Plasma —The liquid part of the blood and lymphatic fluid. Plasma is 92% water, 7% protein and 1% minerals.

RNA —A chemical similar to DNA from which proteins are made. Unlike DNA, RNA can leave the nucleus of the cell.

Short bowel syndrome —Problems related to absorbing nutrients after removal of part of the small intestine.

Sickle cell anemia —Genetic disorder in which red blood cells take on an unusual shape, leading to other problems with the blood.

Synaptic vesicles —Also called neurotransmitter vesicles, these pouches store the various neurotransmitters that are released by nerve cells into the synaptic cleft of a synapse.

Trace minerals —Minerals needed by the body in small amounts. They include: selenium, iron, zinc, copper, manganese, molybdenum, chromium, arsenic, germanium, lithium, rubidium, tin.

Transferrin —A protein synthesized in the liver that transports iron in the blood to red blood cells.

Ulcerative colitis —Inflammation of the inner lining of the colon, characterized by open sores that appear in its mucous membrane.

The Recommended Dietary Allowance (RDA) for zinc is:

• infants: (0–6 months): 3 mg
• infants: (7–12 months): 3 mg
• children (1–3 y): 3 mg
• children (4–8 y): 5 mg
• children (9–13 y): 8 mg
• adolescents (14–18): males, 11 mg, females, 9 mg
• adults: males, 11 mg, females, 8 mg
• pregnancy: 13 mg
• lactation: 14 mg

Zinc in nutritional supplements is available as zinc gluconate, zinc oxide, zinc aspartate, zinc picolinate, zinc citrate, zinc monomethionine and zinc histidine. They are distributed as stand-alone or combination products as tablets, capsules or liquids.

Precautions

Zinc deficiency most often occurs when zinc intake is inadequate or poorly absorbed and it can have serious health consequences. Moderate to severe zinc deficiency is rare in the United States. However, it is highly prevalent in developing countries. The symptoms of severe deficiency include the slowing or cessation of growth and development, delayed sexual maturation, skin rashes, chronic and severe diarrhea , immune system deficiencies, poor wound healing, decreased appetite, impaired taste sensation, night blindness, swelling and clouding of the corneas, and behavioral disorders. These symptoms were first accurately described when a genetic disorder called acrodermatitis enteropathica was linked to zinc deficiency. Although mild dietary zinc deficiency is unlikely to cause such severe symptoms, it is known to contribute to several health problems, especially in young children. Zinc deficiency leads to impaired physical and neuropsychological development, and to an increased risk of life-threatening infections in young children. Individuals at risk of zinc deficiency include:

• infants and children
• pregnant and breastfeeding women, especially teenagers
• patients receiving intravenous feeding
• malnourished individuals, including those with anorexia nervosa
• people with severe or persistent diarrhea
• people with malabsorption syndromes, including celiac disease and short bowel syndrome
• people with inflammatory bowel disease, including Crohn's disease and ulcerative colitis
• people with alcoholic liver disease
• people with sickle cell anemia
• elderly people
• strict vegetarians whose major food staples are grains and legumes because the high levels of phytic acid in these foods lower the absorption of zinc

Fortified foods include many types of breakfast cereals that make it easier to consume the RDA for zinc. However, they also make it easier to consume too much zinc, especially if zinc supplements are also taken. Anyone considering zinc supplementation should accordingly first consider whether their needs could be met by dietary zinc sources and from fortified foods. Intakes between 150 and 450 mg of zinc per day lead to copper deficiency, impaired iron function, reduced immune function, and reduced levels of high-density lipoproteins, the “good cholesterol”. A few isolated cases of acute zinc toxicity have been reported for food or beverages contaminated with zinc present in galvanized containers. Single doses of 225–450mg of zinc are known to induce vomiting. Milder gastrointestinal distress has been reported at doses of 50–150 mg/day of supplemental zinc.

Interactions

The simultaneous administration of zinc supplements and certain antibiotics , such as tetracyclines and quinolones, may decrease absorption of the antibiotic with potential reduction of their action. To prevent this interaction, it is recommended to take the zinc supplements and antibiotics at least two hours apart. Metal chelating agents like penicillamine, used to treat copper overload in Wilson's disease, and diethylenetriamine pentaacetate (DTPA), used to treat iron overload, can lead to severe zinc deficiency. Anticonvulsant drugs , such as sodium valproate, may also cause zinc deficiency. The prolonged use of diuretics may increase urinary zinc excretion, resulting in increased zinc losses. A medication used to treat tuberculosis , ethambutol, has been shown to increase zinc loss in rats.

Interactions of zinc taken with other supplements are as follows:

• Calcium: May lower zinc absorption in postmenopausal women.
• Iron: May reduce the absorption of both iron and zinc.
• Phosphate salts: May lower the absorption of zinc.
• L-cysteine: May increase the absorption of zinc.
• L-histidine: May also enhance the absorption of zinc.

Aftercare

In the case of zinc deficiency, oral zinc therapy usually results in the complete disappearance of symptoms, but it must be maintained indefinitely in individuals with the acrodermatitis enteropathica.

Excessive intake can be corrected by bringing levels back to the RDA values.

Complications

It has been estimated that 82% of pregnant women worldwide are likely to have inadequate zinc intakes. Zinc deficiency has been associated with a number of pregnancy complications, including low birth weight, premature delivery, and labor and delivery complications.

The adverse effects of zinc deficiency on immune system function are also likely to increase complications in children that have infectious diarrhea. Persistent diarrhea contributes to zinc deficiency and malnutrition . Recent research has shown that zinc deficiency may also increase the harmful effects of toxins produced by diarrhea-causing bacteria like E. coli. Zinc supplementation in combination with drinking plenty of liquids has also been shown to significantly reduce the duration and severity of childhood diarrhea.

Parental concerns

Significant delays in growth and weight gain, known as growth retardation or failure to thrive, are common symptoms of mild zinc deficiency in children. But since many of the symptoms associated with zinc deficiency are general and also observed with other medical conditions, parents should not assume that they are due to a zinc deficiency. It is important to consult with a health care professional concerning medical symptoms so that appropriate care can be given.

Resources

books

Larson Duyff, R. ADA Complete Food and Nutrition Guide, 3rd ed. Chicago, IL: American Dietetic Association, 2006.

Challem, J., Brown, L. User's Guide to Vitamins & Minerals. Laguna Beach, CA: Basic Health Publications, 2002.

Bogden, J., ed. Clinical Nutrition of the Essential Trace Elements and Minerals (Nutrition and Health). Totowa, NJ: Humana Press, 2000.

Griffith, H. W. Minerals, Supplements & Vitamins: The Essential Guide. New York, NY: Perseus Books Group, 2000.

Quesnell, W. R. Minerals: The Essential Link to Health. Long Island, NY: Skills Unlimited Press, 2000.

Garrison, R., Somer, E. The Nutrition Desk Reference. New York, NY: McGraw-Hill, 1998.

Newstrom, H. Nutrients Catalog: Vitamins, Minerals, Amino Acids, Macronutrients—Beneficials Use, Helpers, Inhibitors, Food Sources, Intake Recommendations. Jefferson, NC: McFarland & Company, 1993.

Wapnir, R. A. Protein Nutrition and Mineral Absorption. Boca Raton, FL: CRC Press, 1990.

organizations

American Dietetic Association (ADA). 120 South Riverside Plaza, Suite 2000, Chicago, IL 60606-6995. 1-800/877-1600. http://www.eatright.org.

U.S. Department of Agriculture, Food and Nutrition Information Center. National Agricultural Library,10301 Baltimore Avenue, Room 105, Beltsville, MD 20705. (301) 504-5414. http://www.nal.usda.gov.

American Society for Nutrition (ASN). 9650 Rockville Pike, Bethesda, MD 20814. (301) 634-7050. http://www.nutrition.org.

Office of Dietary Supplements, National Institutes of Health. National Institutes of Health, Bethesda, Maryland 20892 USA. http://ods.od.nih.gov.

Monique Laberge Ph.D.

ZINC (REVISED)

Note: This article, originally published in 1998, was updated in 2006 for the eBook edition.

Overview

Zinc is a transition metal that occurs in the center of the periodic table. The periodic table is a chart that shows how chemical elements are related to each other. The space between Groups 2 and 13 is occupied by the transition metals. These metals share many physical and chemical properties in common.

Alloys and compounds of zinc have been known since at least 500 b.c. But zinc metal was not known or used until much later. The reason is that zinc boils away or vaporizes easily when heated. Any effort to release zinc from its compounds also causes the metal to evaporate into the air.

Zinc was probably known in Asia before it was discovered in Europe. Ancient books from both India and China refer to zinc products. Such products were imported to Europe from Asia before they were made in Europe.

SYMBOL
Zn

ATOMIC NUMBER
30

ATOMIC MASS
65.38

FAMILY
Group 12 (IIB)
Transition metal

PRONUNCIATION
ZINK

The most important use of zinc today is in galvanizing other metals. Galvanizing is the process of laying down a thin layer of zinc on the surface of a second metal. Zinc does not corrode (rust) as easily as iron and other metals. So the thin layer of zinc protects iron and other metals from corrosion.

Discovery and naming

Some metals can be obtained from their ores easily. In a few cases, all that is needed is to heat the ore. Heating an ore of zinc releases the free metal. But with zinc, there is an additional problem. Zinc metal sublimates very easily. Sublimation is the process by which a solid changes directly to a gas when heated, without first changing to a liquid. Anyone who wanted to make zinc from its ore would lose the zinc almost immediately by sublimation.

Of course, early people did not understand this process. They may very well have made zinc by heating its ores. But any zinc they made would have floated away immediately. Still, a process for extracting zinc from its ores was apparently invented in India by the 13th century. The process involves heating the zinc ore in a closed container. When zinc vapor forms, it condenses inside the container. It can then be scraped off and used. That method seems to have been passed to China and then, later, to Europe.

In the meantime, ancient people were familiar with compounds and alloys of zinc. For example, there are brass objects from Palestine dating to 1300 b.c. Brass is an alloy of copper and zinc. The alloy may have been made by humans or found naturally in the earth. No one knows the origin of the brass in these objects.

The first European to describe zinc was probably Swiss physician Paracelsus (1493-1541). Paracelsus' real name was Theophrastus Bombastus von Hohenheim. Early in life, he took the name Paracelsus, meaning "greater than Celsus." Celsus was one of the great Roman physicians. Paracelsus wanted the world to know that he was even "greater than Celsus."

Paracelsus was also an alchemist. Alchemy was a kind of pre-science that existed from about 500 b.c. to near the end of the 16th century. People who studied alchemy—alchemists—wanted to find a way to change lead, iron, and other metals into gold. They were also looking for the "secret to eternal life." Alchemy contained too much magic and mysticism to be a real science. But it developed a number of techniques and produced many new materials that were later found to be useful in modem chemistry.

Paracelsus first wrote about zinc in the early 1500s. He described some properties of the metal. But he said he did not know what the metal was made of. Because of his report on the metal, Paracelsus is sometimes called the discoverer of zinc.

The name zinc was first used in 1651. It comes from the German name for the element, Zink. What meaning that word originally had is not known.

Physical properties

Zinc is a bluish-white metal with a shiny surface. It is neither ductile nor malleable at room temperature. Ductile means capable of being drawn into thin wires. Malleable means capable of being hammered into thin sheets. At temperatures above 100°C (212°F), however, zinc becomes somewhat malleable.

Zinc's melting point is 419.5°C (787.1°F) and its boiling point is 908°C (1,670°F). Its density is 7.14 grams per cubic centimeter. Zinc is a fairly soft metal. Its hardness is 2.5 on the Mohs scale. The Mohs scale is a way of expressing the hardness of a material. It runs from 0 (for talc) to 10 (for diamond).

Chemical properties

Zinc is a fairly active element. It dissolves in both acids and alkalis. An alkali is a chemical with properties opposite those of an acid. Sodium hydroxide ("common lye") and limewater are examples of alkalis. Zinc does not react with oxygen in dry air. In moist air, however, it reacts to form zinc carbonate. The zinc carbonate forms a thin white crust on the surface which prevents further reaction. Zinc burns in air with a bluish flame.

Occurrence in nature

The abundance of zinc in the Earth's crust is estimated to be about 0.02 percent. That places the element about number 24 on the list of the elements in terms of their abundance.

A process for extracting zinc from its ores was apparently invented in India by the 13th century.

Zinc never occurs as a free element in the earth. Some of its most important ores are smithsonite, or zinc spar or zinc carbonate (ZnCO₃); sphalerite, or zinc blende or zinc sulfide (ZnS); zincite, or zinc oxide (ZnO); willemite, or zinc silicate (ZnSiO₃); and franklinite [(Zn,Mn,Fe)O (Fe,Mn₂)O₃].

The largest producer of zinc ore in the world today is Canada. Other important producing nations are Australia, China, Peru, the United States, and Mexico. In the United States, more than half of the zinc produced comes from Alaska. Other important producing states are Tennessee, Missouri, Montana, and New York.

Isotopes

Five naturally occurring isotopes of zinc are known. They are zinc-64, zinc-66, zinc-67, zinc-68, and zinc-70. Isotopes are two or more forms of an element. Isotopes differ from each other according to their mass number. The number written to the right of the element's name is the mass number. The mass number represents the number of protons plus neutrons in the nucleus of an atom of the element. The number of protons determines the element, but the number of neutrons in the atom of any one element can vary. Each variation is an isotope.

About eight radioactive isotopes of zinc are known also. A radioactive isotope is one that breaks apart and gives off some form of radiation. Radioactive isotopes are produced when very small particles are fired at atoms. These particles stick in the atoms and make them radioactive.

One radioactive isotope of zinc, zinc-65, has some practical importance. Zinc-65 is used as a tracer to study physical and biological events. A tracer is an isotope whose presence in a system can easily be detected. The isotope is injected into the system at some point. Inside the system, the isotope gives off radiation. That radiation can be followed by means of detectors placed around the system.

Brass is an alloy of copper and zinc.

For example, zinc-65 is used to study how alloys wear out. An alloy can be made using zinc metal. But the zinc used is zinc-65 instead of ordinary zinc. Changes in radiation given off by the radioactive isotope can be followed to find patterns in the way the alloy wears out. Zinc-65 can also be used to study the role of zinc in the human body. A person can be fed food that contains a small amount of zinc-65. The movement of the isotope through the body can be followed with a detector. A researcher can see where the isotope goes and what roles it plays in the body.

Extraction

As with many metals, pure zinc can be prepared from an ore by one of two methods. First, the ore can be roasted (heated in air). Roasting converts the ore to a compound of zinc and oxygen, zinc oxide (ZnO). The compound can then be heated with charcoal (pure carbon ). The carbon takes the oxygen away from the zinc, leaving the pure metal behind:

The other method is to pass an electric current through a compound of zinc. The electric current causes the compound to break apart. Pure zinc metal is produced.

Zinc burns in air with a bluish flame.

Uses

The annual cost of corrosion (rusting) in the United States is estimated to be about $300 billion. This is money lost when metals become corroded and break apart. Buildings and bridges are weakened, cars and trucks rust, farm equipment breaks down, and metal used in many other applications is destroyed. It is hardly surprising that protecting metal from corrosion is an important objective in American industry. One of the most effective ways of providing protection is through galvanizing. Today, about half of all the zinc produced in the United States is used to galvanize other metals. The largest consumers of galvanized metal are the construction and automotive industries.

The second largest use of zinc is in making alloys. An alloy is made by melting and mixing two or more metals. The mixture has properties different from those of the individual metals. Two of the most common alloys of zinc are brass and bronze. Brass is an alloy of zinc and copper. Bronze is an alloy of copper and tin that may also contain a small amount of zinc. Alloys of zinc are used in a great variety of products, including automobile parts, roofing, gutters, batteries, organ pipes, electrical fuses, type metal, household utensils, and building materials.

Compounds

A number of zinc compounds have important uses. Some examples are the following:

Zinc deficiency can interfere with a plant's ability to reproduce.

zinc acetate (Zn(C₂H₃O₂)₂): wood preservative; dye for textiles; additive for animal feed; glazing for ceramics

zinc arsenate (Zn₃(AsO₄)₂): wood preservative; insecticide

zinc borate (ZnB₄O₇): fireproofing of textiles; prevents the growth of fungus and mildew

zinc chloride (ZnCl₂): solder (for welding metals); fireproofing; food preservative; additive in antiseptics and deodorants; treatment of textiles; adhesives; dental cement; petroleum refining; and embalming and taxidermy products

zinc fluorosilicate (ZnSiF₆): mothproofing agent; hardener for concrete

zinc hydrosulfite (ZnS₂O₄): bleaching agent for textiles, straw, vegetable oils, and other products; brightening agent for paper and beet and cane sugar juice

zinc oxide (ZnO): used in rubber production; white pigment in paint; prevents growth of molds on paints; manufacturer of glass; photocopy machines; production of many kinds of glass, ceramics, tile, and plastics

zinc phosphide (Zn₃P₂): rodenticide (rat killer)

zinc sulfate (ZnSO₄): manufacture of rayon; supplement in animal feeds; dyeing of textiles; and wood preservative

Health effects

Zinc is an essential micronutrient for plants, humans, and animals. Zinc deficiency has relatively little effect on the health of a plant, but it interferes with reproduction. Pea plants deprived of zinc, for example, will form flowers. But the flowers will not turn to seeds.

In humans, zinc deficiencies are more serious. Zinc is used to build molecules of DNA. DNA is the chemical in our body that tells cells what chemicals they should make. It directs the reproduction of humans also. Fetuses (babies that have not yet been born) deprived of zinc may grow up to have mental or physical problems. Young children who do not get enough zinc in their diet may experience loss of hair and skin lesions. They may also experience retarded growth called dwarfism. Chemists have now found that zinc plays an essential role in the manufacture of many important chemicals in the human body.

Zinc is an essential micronutrient for humans. But too much or too little can cause health problems.

On the other hand, an excess of zinc can cause health problems, too. Breathing zinc dust may cause dryness in the throat, coughing, general weakness and aching, chills, fever, nausea, and vomiting. One sign of zinc poisoning is a sweet taste in the mouth that cannot be associated with eating sweet foods. Certain compounds of zinc can be harmful to health also. Zinc chloride (ZnCl₂), for example, can cause skin rashes and sore throat.

Zinc

Description

Zinc is a mineral that is essential for a healthy immune system, production of certain hormones, wound healing, bone formation, and clear skin. It is required in very small amounts, and is thus known as a trace mineral. Despite the low requirement, zinc is found in nearly every cell of the body and is a key to the proper function of more than 300 enzymes, including superoxide dismutase. Normal growth and development cannot occur without it.

General use

The U.S. Recommended Dietary Allowance (RDA) for zinc is 5 milligrams (mg) for children under one year of age, 10 mg for children aged one to 10 years old, 15 mg for males 11 years or older, 12 mg for females 11 years or older, 15 mg for women who are pregnant, and 16-19 mg for women who are lactating.

Zinc has become a popular remedy for the common cold . Evidence shows that it is unlikely to prevent upper respiratory infections , but beginning a supplement promptly when symptoms occur can significantly shorten the duration of the illness. The only form of zinc proven effective for this purpose is the zinc gluconate or zinc acetate lozenge. Formulations of 13-23 mg or more appear to be most effective, and need to be dissolved in the mouth in order to exert antiviral properties. Swallowing or sucking on oral zinc tablets will not work. The lozenges can be used every two hours for up to a week or two at most.

People who are deficient in zinc are prone to getting more frequent and longer lasting infections of various types. Zinc acts as an immune booster, in part due to stimulation of the thymus gland. This gland tends to shrink with age, and consequently produces less of the hormones that boost the production of infection-fighting white blood cells. Supplemental zinc, at one to two times RDA amounts, can reverse this tendency and improve immune function.

In another immune stimulant capacity, zinc can offer some relief from chronic infections with Candida albicans, or yeast. Most women will experience a vaginal yeast infection at some time, and are particularly prone to them during the childbearing years. Some individuals appear to be more susceptible than others. One study showed yeast-fighting benefits for zinc even for those who were not deficient in the mineral to begin with. Other supplements that will complement zinc in combating yeast problems are vitamin A, vitamin C , and vitamin E . Another measure that can help to limit problems with Candida is eating yogurt, which is an excellent source of Lactobacillus, a friendly bacteria that competes with yeast. Limiting sweets in the diet and eating garlic or odor-free garlic supplements may also prove helpful.

People who are going to have surgery are well advised to make sure they are getting the RDA of zinc, vitamin A, and vitamin C in order to optimize wound healing. A deficiency of any of these nutrients can significantly lengthen the time it takes to heal. Adequate levels of these vitamins and minerals for at least a few weeks before and after surgery can speed healing. The same nutrients are important to minimize the healing time of bedsores, burns , and other skin lesions.

There are two male health problems that can potentially benefit from zinc supplementation. Testosterone is one of the hormones that requires zinc for production. Men with infertility as a result of low testosterone levels may experience improvement from taking a zinc supplement. Another common condition that zinc can be helpful for is benign prostatic hypertrophy, a common cause of abnormally frequent urination in older men. Taking an extra 50 mg a day for three to six months offers symptomatic relief for some men.

Teenagers are often low in zinc, and also tend to experience more acne than the general population. The doses used in studies have been in the high range, requiring medical supervision, but increasing dietary zinc or taking a modest supplement in order to get the RDA amount is low risk and may prove helpful for those suffering from acne. People should consult a knowledgeable health care provider before taking large doses of any supplement.

There is some evidence that zinc supplementation may slightly relieve the symptoms of rheumatoid arthritis , but the studies are not yet conclusive. It's possible that those who initially had low zinc levels benefited the most.

In 2002, new research showed certain concentrations of zinc improved the effect of a therapy called interferon for some patients with chronic hepatitis C. Although the trial was preliminary, it showed promise for further research into zinc's effects in enhancing interferon therapy.

Zinc is sometimes promoted as an aid for memory. This may be true to the extent that vitamin B₆ and neurotransmitters are not properly utilized without it. However, in the case of people with Alzheimer's disease , zinc can cause more harm than good. Some experiments indicate that zinc actually decreases intellectual function of people with this disease. Under these circumstances, it is probably best to stick to the RDA of 15 mg as a maximum daily amount of zinc.

The frequency of sickle-cell crisis in patients with sickle-cell anemia may be decreased by zinc supplementation. The decrease was significant in one study, although the severity of the attacks that occurred was not affected. Use of zinc supplementation or other treatment for sicklecell anemia, a serious condition, should not be undertaken without the supervision of a health care provider.

Both the retina of the eye, and the cochlea in the inner ear contain large amounts of zinc, which they appear to need in order to function properly. Dr. George E. Shambaugh, Jr., M.D., is a professor emeritus of otolaryngology and head and neck surgery at Northwestern University Medical School in Chicago. In Prevention's Healing with Vitamins, he "estimates that about 25% of the people he sees with severe tinnitus are zinc-deficient." He adds that they sometimes have other symptoms of zinc deficiency. Large doses may be used in order to provide relief for this problem. Medical supervision and monitoring are necessary to undertake this course of treatment.

Topical zinc can be useful for some conditions, including cold sores. It is also available in a combination formula with the antibiotic erythromycin for the treatment of acne. Zinc oxide is a commonly used ingredient in the strongest sun block preparations and some creams for the treatment of diaper rash and superficial skin injuries. Men can use topical zinc oxide to speed the healing of genital herpes lesions, but it is too drying for women to use in the vaginal area.

There is still not enough information on some of the claims that are made for zinc. A few that may have merit are the prevention or slowing of macular degeneration , and relieving psoriasis . One should consult a health care provider for these uses.

Deficiency

It is not uncommon to have mild to moderately low levels of zinc, although serious deficiency is rare. Symptoms can include an increased susceptibility to infection, rashes, hair loss , poor growth in children, delayed healing of wounds , rashes, acne, male infertility, poor appetite, decreased sense of taste and smell, and possible swelling of the mouth, tongue, and eyelids.

A more serious, chronic deficiency can cause severe growth problems, including dwarfism and poor bone maturation. The spleen and liver may become enlarged. Testicular size and function both tend to decrease. Cataracts may form in the eyes, the optic nerve can become swollen, and color vision is sometimes affected by a profound lack of zinc. Hearing is sometimes affected as well.

Since meats are the best sources of zinc, strict vegetarians and vegans are among the groups more likely to be deficient. The absorption of zinc is inhibited by high fiber foods, so people who have diets that are very high in whole grain and fiber need to take supplements separately from the fiber. Zinc is needed in larger amounts for women who are pregnant or breastfeeding. Deficiency during pregnancy may lower fetal birthweight, as well as increase maternal risk of toxemia. A good prenatal vitamin is likely to contain an adequate amount. People over age 50 don't absorb zinc as well, nor do they generally have adequate intake, and may require a supplement. Alcoholics generally have poor nutritional status to begin with, and alcohol also depletes stored zinc.

There is an increased need for most vitamins and minerals for people who are chronically under high stress . Those who have had surgery, severe burns, wasting illnesses, or poor nutrition may require larger amounts of zinc than average.

Some diseases increase the risk of zinc deficiency. Sickle-cell anemia, diabetes, and kidney disease can all affect zinc metabolism. People with Crohn's disease , sprue, chronic diarrhea , or babies with acrodermatitis enteropathica also have an increased need for zinc. Consult a health care provider for appropriate supplementation instructions.

Preparations

Natural sources

Oysters are tremendously high in zinc. Some sources, such as whole grains, beans, and nuts, have good zinc content but the fiber in these foods prevents it from being absorbed well. Foods with better utilized zinc include beef, chicken, turkey, milk, cheese, and yogurt. Pure maple syrup also is a good source of zinc.

Supplemental sources

Zinc supplements are available as oral tablets in various forms, as well as lozenges. Zinc gluconate is the type most commonly used in lozenge form to kill upper respiratory viruses. One should select brands that do not use citric acid or tartaric acid for flavoring, as these appear to impair the effectiveness. The best-absorbed oral types of zinc may include zinc citrate, zinc acetate, or zinc picolinate. Zinc sulfate is the most likely to cause stomach irritation. Topical formulations are used for acne and skin injuries. Oral zinc should not be taken with foods that will reduce its absorption, such as coffee, bran, protein, phytates, calcium , or phosphorus . Supplements should be stored in a cool, dry location, away from direct light, and out of the reach of children.

Precautions

Toxicity can occur with excessively large doses of zinc supplements, and produce symptoms, including fever, cough , abdominal pain, nausea, vomiting , diarrhea, drowsiness, restlessness, and gait abnormalities. If doses greater than 100 mg per day are taken chronically, it can result in anemia, immune insufficiency, heart problems, and copper deficiency. High doses of zinc can also cause a decrease in high density lipoprotein (HDL), or good, cholesterol .

People who have hemochromatosis, are allergic to zinc, or are infected with HIV should not take supplemental zinc. Ulcers in the stomach or duodenum may be aggravated by supplements as well. Those with glaucoma should use caution if using eye drops containing zinc. Overuse of supplemental zinc during pregnancy can increase the risk of premature birth and stillbirth, particularly if the supplement is taken in the third trimester. This increase in adverse outcomes has been documented with zinc dosages of 100 mg taken three times daily.

Side effects

Zinc may cause irritation of the stomach, and is best taken with food in order to avoid nausea. The lozenge form used to treat colds has a strong taste, and can alter the sense of taste and smell for up to a few days.

KEY TERMS

Sickle-cell anemia

—A genetic malformation of red blood cells that can cause periodic crises in sufferers.

Interactions

The absorption of vitamin A is improved by zinc supplements, but they may interfere with the absorption of other minerals taken at the same time, including calcium, magnesium, iron , and copper. Supplements of calcium, magnesium, and copper should be taken at different times than the zinc. Iron should only be taken if a known deficiency exists. Thiazide and loop diuretic medications, sometimes used for people with high blood pressure, congestive heart failure, or liver disease, increase the loss of zinc. Levels are also lowered by oral contraceptives. Zinc can decrease the absorption of tetracycline and quinolone class antibiotics, antacids, soy, or manganese , and should not be taken at the same time of day. Drinking coffee at the same time as taking zinc can reduce the absorption by as much as half. Even moderate amounts of alcohol impair zinc metabolism and increase its excretion. Chelation with EDTA can deplete zinc, so patients undergoing chelation need to supplement with zinc, according to the instructions of the health care provider.

Resources

BOOKS

Bratman, Steven and David Kroll. Natural Health Bible. California: Prima Publishing, 1999.

Feinstein, Alice. Prevention's Healing with Vitamins. Pennsylvania: Rodale Press, 1996.

Griffith, H. Winter. Vitamins, Herbs, Minerals & supplements: the complete guide. Arizona: Fisher Books, 1998.

Jellin, Jeff, Forrest Batz, and Kathy Hitchens. Pharmacist's letter/Prescriber's Letter Natural Medicines Comprehensive Database. California: Therapeutic Research Faculty, 1999.

Pressman, Alan H. and Sheila Buff. The Complete Idiot's Guide to Vitamins and Minerals. New York: alpha books, 1997.

PERIODICALS

Vernarec, Emil. "Zinc May Enhance the Efficacy of Interferon." RN (May 2002): 28.

Judith Turner

Teresa G. Odle

Zinc

Description

Zinc is a mineral that is essential for a healthy immune system, production of certain hormones, wound healing, bone formation, and clear skin. It is required in very small amounts, and is thus known as a trace mineral. Despite the low requirement, zinc is found in nearly every cell of the body and is a key to the proper function of over 300 enzymes, including superoxide dismutase. Normal growth and development cannot occur without it.

General use

The U.S. Recommended Dietary Allowance (RDA) for zinc is 5 milligrams (mg) for children under one year of age, 10 mg for children aged one to 10 years old, 15 mg for males 11 years or older, 12 mg for females 11 years or older, 15 mg for women who are pregnant, and 16-19 mg for women who are lactating.

Zinc has become a popular remedy for the common cold. Evidence shows that it is unlikely to prevent upper respiratory infections, but beginning a supplement promptly when symptoms occur can significantly shorten the duration of the illness. The only form of zinc proven effective for this purpose is the zinc gluconate or zinc acetate lozenge. Formulations of 13-23 mg or more appear to be most effective, and need to be dissolved in the mouth in order to exert antiviral properties. Swallowing or sucking on oral zinc tablets will not work. The lozenges can be used every two hours for up to a week or two at most.

People who are deficient in zinc are prone to getting more frequent and longer lasting infections of various types. Zinc acts as an immune booster, in part due to stimulation of the thymus gland. This gland tends to shrink with age, and consequently produces less of the hormones that boost the production of infection-fighting white blood cells. Supplemental zinc, at one to two times RDA amounts, can reverse this tendency and improve immune function.

In another immune stimulant capacity, zinc can offer some relief from chronic infections with Candida albicans, or yeast. Most women will experience a vaginal yeast infection at some time, and are particularly prone to them during the childbearing years. Some individuals appear to be more susceptible than others. One study showed yeast- fighting benefits for zinc even for those who were not deficient in the mineral to begin with. Other supplements that will complement zinc in combating yeast problems are vitamin A, vitamin C, and vitamin E. Another measure that can help to limit problems with Candida is eating yogurt, which is an excellent source of Lactobacillus, a friendly bacteria that competes with yeast. Limiting sweets in the diet and eating garlic or odor-free garlic supplements may also prove helpful.

People who are going to have surgery are well advised to make sure they are getting the RDA of zinc, vitamin A, and vitamin C in order to optimize wound healing. A deficiency of any of these nutrients can significantly lengthen the time it takes to heal. Adequate levels of these vitamins and minerals for at least a few weeks before and after surgery can speed healing. The same nutrients are important to minimize the healing time of bedsores, burns, and other skin lesions too.

There are two male health problems that can potentially benefit from zinc supplementation. Testosterone is one of the hormones that requires zinc in order to be produced. Men with infertility as a result of low testosterone levels may experience improvement from taking a zinc supplement. Another common condition that zinc can be helpful for is benign prostatic hypertrophy, a common cause of abnormally frequent urination in older men. Taking an extra 50 mg a day for three to six months offers symptomatic relief for some men.

Teenagers are often low in zinc, and also tend to experience more acne than the general population. The doses used in studies have been in the high range, requiring medical supervision, but increasing dietary zinc or taking a modest supplement in order to get the RDA amount is low risk and may prove helpful for those suffering from acne. Consult a knowledgeable health care provider before taking large doses of any supplement.

There is some evidence that zinc supplementation may slightly relieve the symptoms of rheumatoid arthritis, but the studies are not yet conclusive. It's possible that those who initially had low zinc levels benefited the most.

Zinc is sometimes promoted as an aid for memory. This may be true to the extent that vitamin B₆ and neurotransmitters are not properly utilized without it. However, in the case of people with Alzheimer's disease, zinc can cause more harm than good. Some experiments indicate that zinc actually decreases intellectual function of people with this disease. Under these circumstances, it is probably best to stick to the RDA of 15 mg as a maximum daily amount of zinc.

The frequency of sickle-cell crisis in patients with sickle-cell anemia may be decreased by zinc supplementation. The decrease was significant in one study, although the severity of the attacks that occurred was not affected. Use of zinc supplementation or other treatment for sickle- cell anemia, a serious condition, should not be undertaken without the supervision of a health care provider.

Both the retina of the eye, and the cochlea in the inner ear contain large amounts of zinc, which they appear to need in order to function properly. Dr. George E. Shambaugh, Jr., M.D., is a professor emeritus of otolaryngology and head and neck surgery at Northwestern University Medical School in Chicago. In Prevention's Healing with Vitamins, he "estimates that about 25% of the people he sees with severe tinnitus are zinc-deficient." He adds that they sometimes have other symptoms of zinc deficiency. Large doses may be used in order to provide relief for this problem. Medical supervision and monitoring are necessary to undertake this course of treatment.

Topical zinc can be useful for some conditions, including cold sores. It is also available in a combination formula with the antibiotic erythromycin for the treatment of acne. Zinc oxide is a commonly used ingredient in the strongest sun block preparations and some creams for the treatment of diaper rash and superficial skin injuries. Men can use topical zinc oxide to speed the healing of genital herpes lesions, but it is too drying for women to use in the vaginal area.

There is still not enough information on some of the claims that are made for zinc. A few that may have merit are the prevention or slowing of macular degeneration, and relieving psoriasis. Consult a health care provider for these uses.

Deficiency

It is not uncommon to have a mild to moderately low levels of zinc, although serious deficiency is rare. Symptoms can include an increased susceptibility to infection, rashes, hair loss, poor growth in children, delayed healing of wounds, rashes, acne, male infertility, poor appetite, decreased sense of taste and smell, and possibly swelling of the mouth, tongue, and eyelids.

A more serious, chronic deficiency can cause severe growth problems, including dwarfism and poor bone maturation. The spleen and liver may become enlarged. Testicular size and function both tend to decrease. Cataracts may form in the eyes, the optic nerve can become swollen, and color vision is sometimes affected by a profound lack of zinc. Hearing is sometimes affected as well.

Since meats are the best sources of zinc, strict vegetarians and vegans are among the groups more likely to be deficient. The absorption of zinc is inhibited by high fiber foods, so people who have diets that are very high in whole grain and fiber need to take supplements separately from the fiber. Zinc is needed in larger amounts for women who are pregnant or breastfeeding. Deficiency during pregnancy may lower fetal birthweight, as well as increase maternal risk of toxemia. A good prenatal vitamin is likely to contain an adequate amount. People over age 50 don't absorb zinc as well, nor do they generally have adequate intake, and may require a supplement. Alcoholics generally have poor nutritional status to begin with, and alcohol also depletes stored zinc.

There is an increased need for most vitamins and minerals for people who are chronically under high stress. Those who have had surgery, severe burns, wasting illnesses, or poor nutrition may require larger amounts of zinc than average.

Some diseases increase the risk of zinc deficiency. Sickle-cell anemia, diabetes, and kidney disease can all affect zinc metabolism. People with Crohn's disease, sprue, chronic diarrhea, or babies with acrodermatitis enteropathica also have an increased need for zinc. Consult a health care provider for appropriate supplementation instructions.

Preparations

Natural sources

Oysters are tremendously high in zinc. Some sources, such as whole grains, beans, and nuts, have good zinc content but the fiber in these foods prevents it from being absorbed well. Foods with zinc that is better utilized include beef, chicken, turkey, milk, cheese, and yogurt. Pure maple syrup also is a good dose of zinc.

Supplemental sources

Zinc supplements are available as oral tablets in various forms, as well as lozenges. Zinc gluconate is the type most commonly used in lozenge form to kill upper respiratory viruses. Select brands that do not use citric acid or tartaric acid for flavoring, as these appear to impair the effectiveness. The best-absorbed oral types of zinc may include zinc citrate, zinc acetate, or zinc picolinate. Zinc sulfate is the most likely to cause stomach irritation. Topical formulations are used for acne and skin injuries. Oral zinc should not be taken with foods that will reduce its absorption, such as coffee, bran, protein, phytates, calcium, or phosphorus. Supplements should be stored in a cool, dry location, away from direct light, and out of the reach of children.

Precautions

Toxicity can occur with excessively large doses of zinc supplements, and produce symptoms, including fever, cough, abdominal pain, nausea, vomiting, diarrhea, drowsiness, restlessness, and gait abnormalities. If doses greater than 100 mg per day are taken chronically, it can result in anemia, immune insufficiency, heart problems, and copper deficiency. High doses of zinc can also cause a decrease in high density lipoprotein (HDL), or good, cholesterol.

People who have hemochromatosis, are allergic to zinc, or are infected with HIV should not take supplemental zinc. Ulcers in the stomach or duodenum may be aggravated by supplements as well. Those with glaucoma should use caution if using eye drops containing zinc. Overuse of supplemental zinc during pregnancy can increase the risk of premature birth and stillbirth, particularly if the supplement is taken in the third trimester. This increase in adverse outcomes has been documented with zinc dosages of 100 mg taken three times daily.

Side effects

Zinc may cause irritation of the stomach, and is best taken with food in order to avoid nausea. The lozenge form used to treat colds has a strong taste, and can alter the sense of taste and smell for up to a few days.

Interactions

The absorption of vitamin A is improved by zinc supplements, but they may interfere with the absorption of other minerals taken at the same time, including calcium, magnesium, iron, and copper. Supplements of calcium, magnesium, and copper should be taken at different times than the zinc. Iron should only be taken if a known deficiency exists. Thiazide and loop diuretic medications, sometimes used for people with high blood pressure, congestive heart failure, or liver disease, increase the loss of zinc. Levels are also lowered by oral contraceptives. Zinc can decrease the absorption of tetracycline and quinolone class antibiotics, antacids, soy, or manganese, and should not be taken at the same time of day. Drinking coffee at the same time as taking zinc can reduce the absorption by as much as half. Even moderate amounts of alcohol impair zinc metabolism and increase its excretion. Chelation with EDTA can deplete zinc, so patients undergoing chelation need to supplement with zinc, according to the instructions of the health care provider.

KEY TERMS

Acrodermatitis enteropathica— Hereditary metabolic problem characterized by dermatitis, diarrhea, and poor immune status. Oral treatment with zinc is curative.

Benign prostatic hypertrophy— Enlargement of the prostate gland, which surrounds the male urethra, causing frequent urination. This condition is very common in older men.

Hemochromatosis— A hereditary condition that results in excessive storage of iron in various tissues of the body.

Macular degeneration— Deterioration of part of the retina, causing progressive loss of vision. This is the most common cause of blindness in the elderly.

Sickle-cell anemia— A genetic malformation of red blood cells that can cause periodic crises in sufferers.

Tinnitus— Perceived ringing, buzzing, whistling, or other noise heard in one or both ears that has no external source. There are a number of conditions that may cause this.

Resources

BOOKS

Bratman, Steven and David Kroll. Natural Health Bible. California: Prima Publishing, 1999.

Feinstein, Alice. Prevention's Healing with Vitamins. Pennsylvania: Rodale Press, 1996.

Griffith, H. Winter. Vitamins, Herbs, Minerals & Supplements: the Complete Guide. Arizona: Fisher Books, 1998.

Jellin, Jeff, Forrest Batz, and Kathy Hitchens. Pharmacist's letter/Prescriber's Letter Natural Medicines Comprehensive Database. California: Therapeutic Research Faculty, 1999.

Pressman, Alan H. and Sheila Buff. The Complete Idiot's Guide to Vitamins and Minerals. New York: alpha books, 1997.