Researchers are still studying whether supplemental antioxidants might slow the progression of age-related macular degeneration and perhaps prevent noise-related hearing loss. But "no doctor would recommend them for the prevention of cancer, of cardiovascular disease, or of dementia," says Simon.
What about you? Nutritional profiles are not all the same. Recommended intake varies by age, gender, and even race. And genetic differences mean everyone utilizes or responds to vitamins differently, says K. Simon Yeung, a research pharmacist in the Integrative Medicine Service at Memorial Sloan-Kettering Cancer Center. Diet preferences, such as a low-fat or vegetarian regimen, will alter the mix of nutrients taken in. Moreover, lab tests that analyze the nutrients in your system and indicate which ones might need boosting or trimming are, with a few exceptions, not readily available and not often performed. However, keeping tabs on your dining habits for a few days with SuperTracker, a U.S. Department of Agriculture tool, will give you a sense of whether you're on the right course. (It helps you plan, analyze, and track your diet and physical activity.)
Alice Lichtenstein, a professor of nutrition science and policy at Tufts University's Friedman School of Nutrition, worries that supplements give Americans license to continue their unhealthful ways so long as they pop a pill after the steak and hot fudge sundae. A balanced diet is still the best source of nutrients. Adding supplements—or fruits and veggies, for that matter—to a high-calorie diet is not going to work magic. Good health begins with physical activity and a balanced diet that is heavy on fruits, veggies, whole grains, "good" fats, and fish and light on red meat, "bad" fats, and processed food—and not too high in calories. "Nature," says Lichtenfeld, "is probably better than our manufacturers."
Updated on 5/9/2012: This story was originally published on Dec. 9, 2008. It has been updated.