Raise your right hand if you don't take any herbal supplements.

Gee, I don't see any hands, and I probably wouldn't see more than a handful if you were here with me literally instead of virtually.

People with diabetes probably take more supplements than other people. About 36 percent of American adults use complementary and alternative medicine (CAM), much of it in the form of supplements. We spend $20 billion a year for supplements.

Aside from the drain on our bank accounts, we don't have any good proof that any supplements work. None of them.

Supplements are, of course, supplemental to the foods that we eat, our diet. We certainly differ in what we think is a good diet, although we haven't subjected diets and individual foods to clinical trials. That could be coming, but we haven't yet mastered the testing of supplements.

"There is no compelling, credible scientific evidence to suggest that any CAM therapy benefits any medical condition or reduces any medical symptom (pain or otherwise) better than a placebo." This is the conclusion that R. Barker Bausell, Ph.D., reaches on page 254 of his book, Snake Oil Science: The Truth About Complementary and Alternative Medicine (Oxford, 2007, $24.95). He is a bio-statistician and a professor at the University of Maryland. Dr. Bausell was formerly research director of the University of Maryland's Complementary Medicine Program.

With his direct and entertaining style, Dr. Bausell's book is accessible to both a lay and professional audience. He addresses people with diabetes at several points, specifically on page 292, "If you have a potentially life-threatening condition, don't discontinue your insulin...or other treatment, because no CAM therapy is going to come close to matching these drugs' potency.

Snake Oil Science came out in October, but I didn't hear about it until Christmas day, when I read Abigail Zuger's glowing review in The New York Times. I rushed right out and bought my own copy as soon as I could.

Dr. Bausell's book is the perfect complement to The Natural Pharmacist and Complementary & Alternative Medicine (CAM) Supplement Use in People with Diabetes: A Clinician's Guide. I previously reviewed this website and book here.

Why then do we subject ourselves to so many useless supplements? Dr. Bausell says that the placebo effect is the key to how well CAM works. "CAM therapies are nothing more than cleverly packaged placebos," he writes on page 275.

The trouble is that most of these therapies do work -- although weakly, temporarily, and subjectively. While the placebo effect is the main culprit, other stumbling blocks include regression to the mean, the Hawthorne effect, and what he calls "natural history."

Dr. Bausell uses the term natural history in the statistical rather than the usual sense. It's natural for a disease to get better or worse during the course of an illness whether or not it's treated. We also commonly start treatment when the disease is at its worst. When it naturally gets better, we credit the treatment instead of our body.