An overview on dietary supplements and how effective or safe they are.

What are dietary supplements?

Dietary supplements are prepared from food and food products. A dietary supplement contains at least one of the following ingredients: a vitamin, mineral, amino acid, herbal or botanical, or a chemical that is a product of metabolism or a component of the previously mentioned items. A dietary supplement may contain a combination of these ingredients.
Everyone is familiar with vitamin and mineral supplements. Other popular dietary supplements include preparations of herbs such as echinacea, St. John’s wort, ginko biloba and ginseng. Amino acid blends are popular with bodybuilders and other athletes. Substances such as carnitine, creatine and lactate are used in preparations that falsely promise to help you lose fat and improve athletic performance.

How are supplements regulated?

The U.S. Food and Drug Administration (FDA) regulates dietary supplements more like food than drugs, even though some of these substances have drug-like effects. The FDA allows dietary supplements to be sold over the counter, but, unlike drugs, they are not required to undergo rigorous testing for efficacy and safety. Nor are they required by the FDA to meet any quality standards. This means that it can be difficult to know how much of a given substance you are getting. Tests have shown that some brands do not even contain measurable amounts of the substance you are buying the product for!

The best available quality standards for supplements have been set by an independent, nonprofit organization of experts called the U.S. Pharmacopeia (USP). Supplements with USP on their label have passed certain quality tests for purity and potency of ingredients.

Beware of outrageous advertising

According to FDA regulations, it is illegal for manufacturers to make unsupported claims on product labels and advertisements, but many manufacturers make such claims anyway. This is because the responsibility rests with the FDA to prove that the claims are false, rather than with the manufacturer to prove that they are true. Thus, a manufacturer can make a lot of money before getting the word from the FDA to change its advertising. In addition, you might notice small-print disclaimers on some supplement bottles that help manufacturers avoid charges of fraudulent labeling and advertising.

Scan the shelves of a health food store or the pages of magazines that advertise supplements. You will see that many companies make outrageous claims for their products. If the claims are too good to be true, they probably aren’t true.

What about long-term safety?

One of the strongest reservations expressed by nutrition and fitness professionals regarding use of supplements is the lack of data on the long-term safety of many products. Take creatine, a supplement popular among athletes, as an example. Some studies suggest that the right dose of creatine may give power athletes a bit of an edge, so many athletes are popping pills like crazy. Many take doses that are too high, and continue taking the pills longer than they should. Many of these athletes are young and, therefore, more vulnerable to substances (such as carcinogens) that have their strongest effects on rapidly dividing cells. Perhaps supplements such as creatine will be proven harmless, but at this point we just don’t know. Are the benefits really worth the risks?

“Natural” chemicals are still chemicals

As the nutritionist in the opening paragraph pointed out, natural does not mean harmless. Consider dietary supplements with hormone-like effects, such as melatonin and andro (androstenedione). Scientists do not yet understand all of the biochemical pathways these hormones affect. Maybe occasional small doses are safe, but are these substances something you should encourage your clients to play around with?

The same goes for other supplements. Some are effective when used in the right way, some are simply a waste of money, and a few are harmful or have harmful long-term effects. The harmful effects may be from the active ingredients or from other ingredients found in the product. Always remember that supplements can be as strong as drugs. Treat them with respect.

Let the buyer beware

Every once in a while, something really harmful gets produced and promoted. Imagine how bad you would feel if you had recommended it to a client (or taken it yourself). A recent example is a supplement ingredient known as GBL (gamma butyrolactone). GBL is a solvent found in dietary supplements that some claimed to improve sleep, build muscle, boost physical performance and enhance sex. (Hey wait a minute: That sounds like a description of the benefits of exercise. Skip the pills and exercise regularly.)

These products come in liquid and powder form, and were sold in health food stores, on the Internet and in some gyms (be sure these are not on your shelves). At least 120 cases of serious adverse effects (including seizures and coma) and three deaths have been reported in people taking products containing GBL. The FDA has asked manufacturers to recall these products.

When to talk to your doctor

People taking supplements for a health problem should always talk to their health providers and let them know what supplements they are using. Most people taking supplements do not tell their doctors, perhaps out of a fear that their doctors will disapprove. As herbal preparations and other supplements have become more popular, many physicians are learning more about them. Some health providers even recommend these preparations for certain conditions.

If you are taking any medications, ask your pharmacist whether you should be concerned about supplement-drug interactions. For example, it is dangerous to take ginko biloba and aspirin together, because both have potent blood-thinning effects that can lead to dangerous bleeding.

Women who are pregnant, intending to become pregnant or nursing a baby should avoid supplements in the same way that they avoid drugs.


Brown, J.E. Nutrition Now. West/Wadsworth: Belmont, Calif., 1998.

Williams, M. The gospel truth about dietary supplements. ACSM’s Health and Fitness Journal, 1 (1): 24-29, Jan/Feb 1997.

Barbara A. Brehm, Ed.D., is professor of exercise and sport studies at Smith College, Northampton, Mass.

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