NUTRITION, DIETARY SUPPLEMENTS

Although Americans have long been consuming vitamin and mineral supplements, it was only in the 1980s and 1990s that a direct relationship between diet and health (and, therefore, the potential beneficial role for nutrient supplements beyond the minimum amounts required to avoid deficiency) became apparent. The elderly population is the most diverse and heterogeneous of any age group, and determining the nutritional needs of older adults is challenging because their physiology, medical conditions, lifestyles, and social situations are different from those of younger people.

Overview of dietary supplement use

Findings from the Third National Health and Nutrition Examination Survey, 1988–1994 (NHANES III) suggest that 40 percent of Americans use dietary supplements. Total sales of dietary supplements in the United States in 2000 were estimated to be 16 billion dollars. Between the years 1990 and 1997, the prevalence of high-dose vitamin (megavitamins) use increased by 130 percent, while the use of high-dose herbal supplements rose 380 percent. Supplement use has been shown to increase with age, is consistent with more healthful lifestyles, and is reflective of higher family income and level of education. Approximately 56 percent of middle-aged and older adults consume at least one supplement on a regular basis.

Regulation of dietary supplements

The Dietary Supplement Health and Education Act (DSHEA) of 1994 laid the foundation for the current regulatory framework for dietary supplements. Dietary supplements have been defined by DSHEA as products (other than tobacco) intended to supplement the diet that bear or contain one or more of the following dietary ingredients: a vitamin; a mineral; an herb or other botanical; an amino acid; a dietary substance to supplement the human diet by increasing the total dietary intake; or a concentrate, metabolite, constituent, extract, or combination of any of the ingredients described above. This law amended the Federal Food, Drug, and Cosmetic Act of 1938 "to establish standards with respect to dietary supplements."

Under DSHEA, the U.S. Food and Drug Administration (FDA) regulates safety, manufacturing, and product information—such as claims on product labels, package inserts and accompanying literature. However, the FDA cannot require testing of dietary supplements prior to marketing.

Key nutrients for elderly persons

There is increasing evidence that B vitamins play a role in preventing blood vessel diseases and in maintaining normal neurologic function. Antioxidants help fight oxidation in the body, and thereby reduce chemical damage that may contribute to heart disease, cancer, cataracts, macular degeneration of the eyes, neurodegenerative diseases, and possibly even aging itself. The need for vitamin D and calcium in the prevention of osteoporosis due to bone mineral loss is well established.

Most elderly people do not get enough calcium. The optimal intake of calcium is not known, but the current recommended adequate intake (AI) for men and women over age fifty is set at 1,200 mg daily. Vitamin D status diminishes with age due to decreased dietary intake, decreased vitamin D absorption, decreased sun exposure, decreased skin synthesis of vitamin D, and decreased formation of active vitamin D in the kidney. Results from a number of research studies indicate that intake of calcium and vitamin D supplements can reduce the loss of minerals from bone.

Vitamin B₁₂ is another nutrient that has been shown to be deficient in elderly persons. Ten to 30 percent of older adults may be unable to absorb naturally occurring vitamin B₁₂ from their diet due to gastrointestinal disorders, but they can absorb B₁₂ in fortified foods and dietary supplements. It is advisable for adults over 50 to meet their recommended intake by consuming foods fortified with B₁₂ or supplement containing B₁₂

Folate, another B vitamin, plays a crucial role in modulating the level of homocysteine, an amino acid normally found in blood. There is accumulating evidence that elevated homocysteine is an independent risk factor for heart disease and stroke. In the United States, fortified foods such as cereal and grains are a major source of folic acid, the synthetic form of folate, and the diets of most adults now provide recommended amounts of folate.

Numerous epidemiological studies have suggested that foods rich in dietary antioxidants, such as vitamin C, vitamin E, selenium, and the carotenoids, may reduce the risk for chronic disease. However, insufficient evidence exists to conclude that such nutrients, even in very high doses, such as may occur in the form of dietary supplements, will reduce the risk of disease.

Supplementation with modest doses of a combination of micronutrients may enhance immune function in older adults. For example, both zinc and vitamin B₆ deficits have been shown to alter immune function in the elderly, a condition which can be improved with supplementation.

Evidence is emerging from well-designed randomized clinical trials to suggest some herbal supplements are beneficial. However, it is not fully understood how many herbal preparations work, nor is the active component always known. Of the nearly two thousand herbal products in use, very few have been adequately tested for efficacy and toxicity. Concern also exists for potential herb-drug interactions (as well as drug-supplement interactions)—an estimated 15 million adults took prescription medications concurrently with herbal remedies and/or high-dose vitamins in 1997.

A continuing challenge for consumers, as well as health care professionals, is the lack of information about dietary supplements, including their effectiveness, safety, standard dosage, side effects, interactions with medications and foods, and how they affect medical conditions. For some supplements, the evidence is considered substantive enough to warrant recommendations for usage, notably for calcium, vitamin D, vitamin B₁₂ and folic acid. When considering a supplement, consumers should look for ingredients in products with the U.S.P. notation, which indicates that the manufacturer followed standards of preparation established by the U.S. Pharmacopoeia. It is important to realize that the label term natural does not guarantee that a product is safe, and consumers should read all labeling and dosage information carefully.

Rebecca B. Costello

See also Biomarkers of Aging; DNA Damage and Repair; Life Span Extension; Nutrition; Stress.

BIBLIOGRAPHY

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