The Good: Groups for whom supplements are recommended
Women of child-bearing potential
Folic acid. To reduce the risk of neural tube defects (such as spina bifida) developing during pregnancy, it's recommended that all women capable of becoming pregnant consume a supplement with 400 micrograms (0.4 mg) folic acid. Waiting until you're pregnant or planning a pregnancy isn't a good idea, as the neural tube closes before many women even know they're pregnant, and 50% of pregnancies are unplanned. Most multivitamins provide 400 - 600 micrograms of folic acid.

Adults over age 50
Vitamin B12. Food sources of vitamin B12 are bound to protein, and acid is needed to release the vitamin so that it can be absorbed. Stomach acid production decreases in some people over the age of 50, making it difficult to digest food sources of vitamin B12. For this reason, it's recommended that adults over 50 meet the RDA for vitamin B12 (2.4 micrograms) from a synthetic source - either a supplement or foods that have been fortified with the vitamin. Most multivitamins provide the RDA for vitamin B12.

Vitamin D. Low levels of vitamin D are associated with risk of osteoporosis, and may also be linked with risk of colon cancer and multiple sclerosis. With aging, the skin's ability to synthesize vitamin D from sunlight exposure decreases, so the need for dietary vitamin D increases to 400 - 600 International Units (I.U.) per day. Vitamin D is found in only a few foods (e.g., fluid milk, some margarines, salmon) and most diets don't provide amounts of the vitamin recommended for older adults. Multivitamin supplements typically provide 400 I.U. of vitamin D.

Vegetarians
Vitamin B12: Vegan vegetarians require a vitamin B12 supplement to meet the RDA, since this vitamin is found only in animal products. Although vitamin B12 deficiency develops slowly, if undetected it can lead to permanent damage to the nerves and spinal cord.

Vitamin D: Most vegan vegetarians will require a supplement to meet the recommended intake of vitamin D, unless their diet includes regular use of foods that have been fortified with the vitamin.

Other Nutrients: Other nutrients that may be low in vegetarian diets (either because plant foods provide lower amounts, or because they contain substances that reduce absorption) include iron, zinc and calcium.

What about athletes???
Some studies suggest that high mileage distance runners may have increased needs for iron, but there is no evidence that this is the case for cyclists, who don't experience the gastrointestinal and urinary blood loss seen in some runners. And although iron deficiency can definitely affect physical performance, supplementation by those who are not iron deficient is of no benefit. If you suspect that you may be iron deficient (you're a woman with heavy menstrual losses, or a blood donor), have your doctor check your iron status. High intakes of iron by those who aren't deficient can interfere with absorption of other minerals.

What about decreasing risk of heart disease, cancer, Alzheimer's disease???
In recent years, several research studies have suggested that people who took supplements were at lower risk of a number of chronic diseases. However, most of these studies were observational studies, in which participants were assessed at baseline, and followed over time. After a number of years, the habits of those who developed a disease were compared to those who did not, to see if disease risk was lower in supplement users. These studies, however, merely show associations between supplement use and reduced risk of the disease, rather than demonstrating that supplement use is actually responsible for disease prevention. In most cases, many other factors vary between those who do and do not use supplements (e.g., income, education, diet, physical activity), and these factors, rather than the supplement use, may be responsible for reducing the risk of disease. Although scientists attempt to control for these differences statistically in observational studies, they are not always successful, as shown by the fact that randomized double-blind studies - the "gold standard" - may show opposite results.

The best example of this comes from the recent Women's Health Initiative (WHI). Observational studies had suggested that postmenopausal women who used hormone replacement were at a 40-50% lower risk of heart disease, so the WHI was designed to test this directly. Postmenopausal women were randomly assigned to receive hormone replacement therapy or placebos. The results, rather than showing a beneficial effect of hormone use in preventing heart disease, actually showed a higher risk in hormone users (Manson et al, 2003). Similarly, studies suggesting that dietary intakes and blood levels of beta-carotene were associated with reduced risk of cancer and heart disease led to randomized trials using beta-carotene supplements. The results of these studies, however, did not show any benefits of supplementation, and in some cases they appeared to increase the risk (Dagenais 2000). In other words, although observational studies indicated that beta-carotene was associated with reduced risks, randomized trials showed that the association was not causal. It's possible that substances in fruits and vegetables other than beta-carotene may be responsible for the risk reduction seen in observational studies. Research in this area is continuing actively, and future studies will undoubtedly provide new information. At present, however, there are no studies demonstrating that supplements providing more than recommended intakes of nutrients are effective in preventing chronic disease in healthy people.

The Bad: More is not better
The committees that established the RDAs also acknowledged that adverse effects may also occur as a result of excessive intakes of vitamins and minerals. Recently, this possibility has increased considerably with fortification of the food supply and increased use of supplements. In recognition of this, they established a "Tolerable Upper Intake Level", or UL, that represents the amount of a nutrient that can be tolerated by the body when consumed on a daily basis over a prolonged period of time. As intakes increase above the UL, the probability of experiencing the adverse effect associated with excessive intakes increases. Adverse effects range from those that are relatively benign (e.g., diarrhea with too much magnesium) to those that are serious and potentially irreversible (e.g., increased risk of birth defects with too much vitamin A, nerve damage with too much vitamin B6). The UL is not a recommended level, but instead, is an amount that intakes should remain below. Information on the UL for various vitamins and minerals, and the adverse effects associated with excessive intakes can be found at the Office of Dietary Supplements website referenced at the end of this article.

The Ugly: What you don't know could hurt you
There is no requirement for supplement manufacturers to prove that their products are either safe or effective: "Manufacturers do not have to provide FDA with evidence that dietary supplements are effective or safe; however, they are not permitted to market unsafe or ineffective products. Once a dietary supplement is marketed, FDA has to prove that the product is not safe in order to restrict its use or remove it from the market. In contrast, before being allowed to market a drug product, manufacturers must obtain FDA approval by providing convincing evidence that it is both safe and effective." http://ods.od.nih.gov/factsheets/generalbackground_pf.html (Accessed January 29, 2004).

The supplement may not contain what is listed on the label: "Dietary supplements are not required to be standardized in the United States. In fact, no legal or regulatory definition exists in the United States for standardization as it applies to dietary supplements. Because of this, the term 'standardization' may mean many different things. Some manufacturers use the term standardization incorrectly to refer to uniform manufacturing practices; following a recipe is not sufficient for a product to be called standardized. Therefore, the presence of the word 'standardized' on a supplement label does not necessarily indicate product quality. " http://ods.od.nih.gov/factsheets/generalbackground_pf.html (Accessed January 29, 2004).

The supplement may contain substances that are not listed on the label: The International Olympic Committee analysed 634 non-hormonal nutritional supplements obtained in 13 countries, purchased primarily in stores (over 91%) or on the internet (8%). Fifteen percent of all supplements contained prohormones that were not declared on the label, and that could lead to positive doping tests. Further information on the IOC report can be located at http://multimedia.olympic.org/pdf/en_report_324.pdf (Accessed January 29, 2004)

An example of the need for caution is shown in the following Safety Warning from the United States Food and Drug Administration. A company marketed dietary supplements/herbal products for prostate health and for strengthening the immune system. There was no requirement to prove safety or efficacy before putting them on the market. Over time, however, consumers developed serious side effects from their use, and they were found to contain (unlabeled) prescription drug ingredients. Following this finding, a safety warning was issued and the company recalled their products.

"PC SPES, SPES (BotanicLab) Consumers were warned to stop using the dietary supplement / herbal products PC SPES and SPES capsules because they contain undeclared prescription drug ingredients that could cause serious health effects if not taken under medical supervision. Laboratory analysis of the products by the California Department of Health Services found PC SPES contains warfarin and SPES contains alprazolam. Warfarin and alprazolam are available only by prescription and sold either by their generic names or the trade names, Coumadin and Xanax. PC SPES and SPES are respectively marketed 'for prostate health' and 'strengthening the immune system'. BotanicLab, the manufacturer of the products, voluntarily recalled PC SPES and SPES nationwide." http://www.fda.gov/medwatch/SAFETY/2002/safety02.htm#spes (Accessed January 29, 2004)

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The Bottom Line
For some individuals (women of child-bearing potential, people over 50, strict vegetarians), using of a "1-a-day" vitamin/mineral supplement with amounts of nutrients that approximate the RDA is an effective way of meeting nutrient intake recommendations. Note, however, that most 1-a-day supplements provide relatively small amounts of calcium, so those with diets that are inadequate in dairy products may need a calcium supplement. For those who don't fall in one of the above groups, taking a 1-a-day supplement is unlikely to be harmful.

When choosing a vitamin-mineral supplement, stick to reputable brands and intakes that are not excessive. You don't have to spend a lot of money to purchase a good supplement - the cost shouldn't be more than about ten cents a day. If you're paying more, you're wasting your money.

Remember that excessive intakes of vitamin/mineral supplements have not been shown to be beneficial, and can expose you to unnecessary risks.

Remember that taking a supplement will not "make up" for a poor diet. There's an old saying amongst nutrition types: A poor diet plus a supplement does not equal a good diet, it just equals a poor diet plus a supplement.

Caveat emptor!

For More Information
Office of Dietary Supplements:
Click on Dietary Reference Intakes (DRI) and Recommended Dietary Allowances (RDA). On the next page, click on "Minerals" or "Vitamins" under "DRI Tables" to download pdf files that list the function, recommended intake, Upper Level, food sources, side effects of excessive intakes, and any special considerations.

Click on Fact Sheets on Dietary Supplements. On the next page, you can select fact sheets for a list of nutrient (e.g., iron, folate) and non-nutrient (e.g., ephedra, garlic) supplements.

Consumer Lab: This site contains information about analysis of supplement products, to determine whether they contain the substances listed on the label; and do not contain other unlabeled substances. Recently, they have started to test supplements for the presence of substances banned by the International Olympic Committee.

United States Olympic Committee:
On this site, scroll all the way down to the bottom of the page, where you can obtain pdf files on United States Olympic Committee guidelines on a variety of nutrient and non-nutrient supplements.

Manson JE, Hsia J, Johnson KC, et al. Estrogen plus progestin and the risk of coronary heart disease. New England Journal of Medicine 2003;349(6):523-534.

Dagenais GR, Marchioli R, Yusuf S, Tognoni G. Beta-carotene, vitamin C, and vitamin E and cardiovascular diseases. Current Cardiology Reports 2000; 2(4):293-299.