Nearly everyone agrees on this much: People should get as many nutrients as possible through a healthy diet. Beyond that, they should read as much as they can and consult their doctor. Advice on whether to take vitamins or what kind can vary by gender, age and a person's medical condition.
But it can be difficult to decipher the pros and cons of vitamins-of-the-moment, where new research challenging the benefit of a nutrient can refute long-held beliefs.
It happened in 2005 with vitamin E. Praised since the 1960s for near-miracle properties such as helping ward off cardiovascular disease and cancer, vitamin E's cachet was lost when a study by Dr. Edgar R. Miller III showed high doses (more than 400 international units) increased the risk of death among the sick and elderly.
Miller, an associate professor of medicine and epidemiology at the Johns Hopkins School of Medicine, said the vitamin E story proves that more rigorous research is necessary for many supplements on the market. The foundation of many vitamin E fans' support came from studies that surveyed health-conscious people, a demographic that likely skewed results, he said. The most effective way to evaluate if a supplement is effective is with clinical trials that offer placebos to some subjects and vitamins to others, he said.
"Vitamin E can be sold and promoted without showing evidence," he said. "Companies don't have to show efficacy. It is an unregulated industry and they don't have to back up their research."
Miller urges caution for most supplements, with a few exceptions: Pregnant women should take folic acid to reduce the possibility of neural tube defects, and many people can benefit from Omega-3 fatty acids, which he says can decrease the risk of heart disease.
As for the rest of us: "People would do better by exercising and spending their money on fruits and vegetables."
Dr. Meir Stampfer, professor of nutrition and epidemiology at the Harvard School of Public Health, disagrees with much of what Miller has to say. He wasn't convinced by Miller's findings about the ills of vitamin E. With the average American diet inadequate in many nutrients, Stampfer recommends a multivitamin, takes one himself and does not shun large doses of vitamin E.
"By taking a multivitamin, you have just knocked that whole issue off the table," he said. "Vitamin B-6 is one that is often inadequate. The average person doesn't know where vitamin B-6 comes from - even some experts don't know where it comes from. The point is, why should people have to worry about that? They've got enough to think about when it comes to nutrition."
