The bath water.

The excitement was palpable. In the 1980s and '90s, studies suggested that vitamins or other dietary supplements might lower the risk of heart disease, cancer, cataracts, osteoporosis, arthritis, hot flashes, and other health problems.

Researchers were especially optimistic about antioxidants like vitamin E, vitamin C, and beta-carotene. That sense of something big just over the horizon spread through scientific journals, the media (including us), and even the grant-making offices of the National Institutes of Health. Under pressure from the supplement industry, Congress added fuel to the fire by passing a law that made it easier for companies to market supplements and tougher for the Food and Drug Administration to yank unsafe ones off the market. Between 1996 and 2004, supplement sales doubled, to some $20 billion a year.

In the past two decades, researchers have put supplements to the test in carefully controlled trials in hundreds--or, in many cases, tens of thousands--of people. On page 12 we report on the latest--on vitamin E and heart disease. The results, like many previous ones, were disappointing. Vitamin E not only failed to cut the risk of heart disease; it increased the risk of heart failure.

The results reminded me of beta-carotene. In three major trials, large doses failed to prevent cancer, and in two of them, the supplement actually increased the risk of lung cancer in smokers.

Other research has also flopped. DHEA didn't pan out as a sexual tonic. Energy levels weren't boosted by ginseng. Ginkgo biloba had little, if any, effect on memory. Colds weren't warded off by Echinacea. And chitosan didn't help people lose weight.

So why do we continue to spend billions every year on dietary supplements?

Because the people who sell them to us are very smart, for manufacturers, retailers, and some physicians--not to mention the magazines and radio and television stations that carry advertising--supplements are big business. Pill makers design their labels as though they were selling bottles of wine or olive oil. And their ads know what buttons to push to attract consumers who are desperate for a way to avoid or treat cancer, Alzheimer's disease, chronic fatigue syndrome, attention-deficit disorder, you name it.

That's the dirty bath water.

Just make sure you don't throw out the baby: some supplements clearly are beneficial. Calcium and vitamin D reduce the risk of osteoporosis and folic acid prevents neural tube birth defects. And there's promising evidence that folic acid can reduce heart disease and stroke risk; glucosamine and chondroitin can help curb arthritis; a high-dose mixture of vitamin E, vitamin C, beta-carotene, and zinc can slow the progression of macular degeneration; and saw palmetto can help relieve the symptoms of an enlarged prostate. And an ordinary multivitamin-and-mineral is a smart, safe, "insurance policy."

The bottom line: until good studies show that a supplement is safe and effective, maintain a healthy skepticism. Don't get suckered into buying false promises. The truth is that most of the pills and potions that line store shelves and Web sites are little more than snake oil, and behind their lofty references to scientific research, most of the marketers are little more than MBA-toting snake-oil sellers.

Michael F. Jacobson, Ph.D.

Executive Director

Center for Science in the Public Interest