What Are Dietary Supplements?

For decades, the Food and Drug Administration regulated dietary supplements as foods, in most circumstances, to ensure that they were safe and wholesome, and that their labeling was truthful and not misleading. An important facet of ensuring safety was FDA's evaluation of the safety of all new ingredients, including those used in dietary supplements, under the 1958 Food Additive Amendments to the Federal Food, Drug, and Cosmetic Act (FD&C Act). However, with passage of the Dietary Supplements Health and Education Act of 1994 (DSHEA), Congress amended the FD&C Act to include several provisions that apply only to dietary supplements and dietary ingredients of dietary supplements. As a result of these provisions, dietary ingredients used in dietary supplements are no longer subject to the premarket safety evaluations required of other new food ingredients or for new uses of old food ingredients. They must, however, meet the requirements of other safety provisions.

Signed by President Clinton on October 25, 1994, the DSHEA acknowledges that millions of consumers believe dietary supplements may help to augment daily diets and provide health benefits. In the findings associated with the DSHEA, Congress stated that there may be a positive relationship between sound dietary practice and good health, and that, although further scientific research is needed, there may be a connection between dietary supplement use, reduced health-care expenses, and disease prevention.

Traditionally, dietary supplements referred to products made of one or more of the essential nutrients, such as vitamins, minerals, and protein. But DSHEA broadens the definition to include, with some exceptions, any product intended for ingestion as a supplement to the diet. This includes vitamins; minerals; herbs, botanicals, and other plant-derived substances; and amino acids (the individual building blocks of protein) and concentrates, metabolites, constituents and extracts of these substances.

Dietary supplements come in many forms, including tablets, capsules, powders, softgels, gelcaps, and liquids. Though commonly associated with health food stores, dietary supplements also are sold in grocery, drug and national discount chain stores, as well as through mail-order catalogs, TV programs, the Internet, and direct sales.

One thing dietary supplements are not is drugs. A drug, which sometimes can be derived from plants used as traditional medicines, is an article that, among other things, is intended to diagnose, cure, mitigate, treat, or prevent diseases. Before marketing, drugs must undergo clinical studies to determine their effectiveness, safety, possible interactions with other substances, and appropriate dosages, and FDA must review these data and authorize the drugs' use before they are marketed. FDA does not authorize or test dietary supplements.

A product sold as a dietary supplement and touted in its labeling as a new treatment or cure for a specific disease or condition would be considered an unauthorized--and thus illegal--drug. Labeling changes consistent with the provisions in DSHEA would be required to maintain the product's status as a dietary supplement.

Claims that tout a supplement's healthful benefits have always been a controversial feature of dietary supplements. Manufacturers often rely on them to sell their products. But consumers often wonder whether they can trust them.

Disease claims show a link between a food or substance and a disease or health-related condition. FDA authorizes these claims based on a review of the scientific evidence. Or, after the agency is notified, the claims may be based on an authoritative statement from certain scientific bodies, such as the National Academy of Sciences, that shows or describes a well-established diet-to-health link. As of this writing, certain dietary supplements may be eligible to carry disease claims, such as claims that show a link between:

  • the vitamin folic acid and a decreased risk of neural tube defect-affected pregnancy, if the supplement contains sufficient amounts of folic acid
  • calcium and a lower risk of osteoporosis, if the supplement contains sufficient amounts of calcium
  • psyllium seed husk (as part of a diet low in cholesterol and saturated fat) and coronary heart disease, if the supplement contains sufficient amounts of psyllium seed husk.

Nutrition support claims can describe a link between a nutrient and the deficiency disease that can result if the nutrient is lacking in the diet. For example, the label of a vitamin C supplement could state that vitamin C prevents scurvy. When these types of claims are used, the label must mention the prevalence of the nutrient-deficiency disease in the United States.

These claims also can refer to the supplement's effect on the body's structure or function, including its overall effect on a person's well-being. These are known as structure-function claims.

Examples of structure-function claims are:

  • Calcium builds strong bones.
  • Antioxidants maintain cell integrity.
  • Fiber maintains bowel regularity.

If shoppers find dietary supplements whose labels state or imply that the product can help diagnose, treat, cure, or prevent a disease (for example, "cures cancer" or "treats arthritis"), they should realize that the product is being marketed illegally as a drug and as such has not been evaluated for safety or effectiveness.

Consumers need to be on the lookout for fraudulent products. These are products that don't do what they say they can or don't contain what they say they contain. At the very least, they waste consumers' money, and they may cause physical harm.

Nutrition experts agree that the Food Guide Pyramid offers a reliable and easy-to-follow plan for healthful eating. Eating the "pyramid way" means choosing the appropriate number of servings and a variety of foods from each of the five Food Guide Pyramid food groups. This is generally the best way to get all the vitamins, minerals, and other nutrients you need.

However, even people with the best intentions sometimes fall short on their nutrient intake. For some people a vitamin/mineral supplement offers benefits that are both safe and effective. A vitamin/mineral supplement may help when

  • your hectic lifestyle frequently keeps you from eating the recommended number of servings from the food guide pyramid,
  • you are on a very low-calorie weight loss diet,
  • you are elderly and not eating as much as you should,
  • you are a strict vegetarian,
  • you can't drink milk or eat cheese and yogurt,
  • or you are a woman of child-bearing age who doesn't get enough folate from fruits, vegetables, beans, and grains.

To help prevent birth defects of the brain and spine, known as neural tube birth defects, health authorities recommend that women who are planning to become pregnant consume 400 micrograms of folic acid daily at least one month prior to conception.

Determination of the presence or absence of a deficiency of one or more of the micronutrient minerals (usually described as trace elements) can be a complex problem, frequently requiring the integration of clinical, nutritional and biochemical data. Almost invariably, laboratory investigations are required and this short review describes the more common techniques applied for the various essential trace elements. Using a combination of techniques it is usually possible to determine, with confidence, whether an individual subject or small groups of subjects have a deficiency of a specific trace elements, but simple reliable tests which can be used in population studies are still lacking for several key elements. This problem appears most acute for studies of chromium, copper and zinc, deficiencies of which may have important roles in the pathogenesis of a variety of human disorders.

Vitamin supplements are increasingly being used to prevent diseases such as neural tube birth defects, heart attacks, and certain cancers. The amount of vitamin supplements used for disease prevention is often much higher than the RDA levels. A classic example is the use of vitamin nicotinic acid (also called Niacin) in high doses to increase the good HDL cholesterol and lower triglycerides in the blood. In order to consume these higher levels of vitamins, diet alone may not be enough, and vitamin supplements are necessary.

A nutrition intervention trial involving > 3000 participants was conducted in Linxian, China, where the esophageal and stomach cancer mortality rates are among the highest in the world and suspicion exists that chronic deficiencies of multiple nutrients are etiologically involved. The trial was randomized, double-blind, and placebo-controlled and tested the effect of multivitamin and multimineral supplements in reducing cancer incidence and mortality in adults with cytologically detected esophageal dysplasia. Endoscopic and cytologic examinations of samples of trial participants during the intervention allowed evaluation of intermediate endpoints in esophageal and gastric carcinogenesis, including asymptomatic histologic precancerous lesions and early invasive cancer, epithelial proliferation, and cytologic abnormalities. Results from these ancillary studies suggest that multivitamin and multimineral supplementation may decrease proliferation and enhance cytologic reversion to non-dysplasia.

The coexistence of multiple micronutrient deficiencies is a widespread public health problem in many regions of the world. Interactions between zinc deficiency and vitamin A metabolism have been reported but no longitudinal studies have evaluated the effect of iron deficiency on vitamin A.

The objective of this study was to investigate the effect of supplementation with iron, zinc, or both on vitamin A and its metabolically related proteins retinol binding protein (RBP) and transthyretin.

The study was a longitudinal, double-blind, placebo-controlled trial in which 219 rural Mexican children aged 18?36 mo were randomly assigned to receive 20 mg Zn/d, 20 mg Fe/d, 20 mg Zn/d plus 20 mg Fe/d, or placebo.

Six months after supplementation, plasma retinol increased in all supplemented groups. Compared with placebo, zinc supplementation was associated with significantly higher plasma retinol and transthyretin but the increase in RBP was not significant. Iron supplementation significantly increased plasma retinol, RBP, and transthyretin. Supplementation with zinc plus iron significantly increased plasma retinol but not RBP or transthyretin. Children deficient in zinc, iron, or vitamin A (as indicated by nutrient plasma concentration) at the beginning of the study had a significantly greater increase in retinol than did children with adequate nutrient status.

Conclusions: Supplementation with zinc, iron, or both improved indicators of vitamin A status. The results of this study agree with previous observations of a metabolic interaction between zinc and vitamin A and suggest an interaction between iron and vitamin A metabolism.

Before taking a supplement, be aware that health risks exist for some people. For instance, it is not recommended that pregnant women take more than 5000 IU daily of vitamin A from retinol (a form of vitamin A). Too much vitamin A can increase the risk of birth defects. In addition, too much iron can increase risk of chronic disease, so it is recommended that men and post-menopausal women not routinely take iron supplements at levels higher than 100 percent of the Daily Value. Check the label to be sure. Consult a registered dietitian or doctor before taking a single supplement.

For those who choose to take a supplement, it is best to select a product that provides no more than 100 percent of the Daily Value for vitamins and minerals. Check the Nutrition Facts panel on the label.

  • Dietary Supplement Health And Education Act Of 1994. U. S. Food and Drug Administration Center for Food Safety and Applied Nutrition
  • Paula Kurtzweil. An FDA Guide to Dietary Supplements. Publication No. (FDA) 99-2323
  • Do You Need a Multivitamin/Mineral Supplement? The American Dietetic Association/National Center for Nutrition and Dietetics
  • Jackson MJ. Diagnosis and detection of deficiencies of micronutrients: minerals. Br Med Bull 1999;55(3):634-42
  • PR Taylor, GQ Wang, Et al. Effect of nutrition intervention on intermediate endpoints in esophageal and gastric carcinogenesis. Am. J. Clinical Nutrition 1995 62
  • Elsa C Muñoz, Jorge L Rosado, Et al. Iron and zinc supplementation improves indicators of vitamin A status of Mexican preschoolers. Am J Clin Nutr 2000 71: 789-794

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