Whole foods will always fare better than micronutrient supplements.
Children are often urged by well-meaning adults to eat plenty of fruits and vegetables. Well, that might also be the best advice for preventing certain types of cancer. Numerous epidemiological studies have shown that consuming fruits and vegetables is associated with a lower risk of cancer and better outcomes among cancer survivors.
During the past 20 years, many large clinical trials have tried to determine the cancer-fighting power of specific micronutrients (vitamins and minerals) in food by testing them in pill form in healthy men and women, in heavy smokers and in cancer survivors. Not only did large doses of micronutrients fail to prevent cancer, in some trials micronutrients increased the rate of the very cancer the trial was designed to prevent.
“The assumption that ‘oh, if a little is good, a lot can’t possibly hurt me’ has been proven incorrect,” says Susan Mayne, an epidemiologist at Yale University in New Haven, Conn.
People confuse the effect of micronutrients in a test tube and the effect of micronutrients in a body. They’re really different.
Micronutrients are trace substances found in food that help promote the growth of cells and tissues. Although the body needs only small amounts of micronutrients, their absence can produce serious health problems. For example, a lack of iron can cause iron-deficiency anemia, and a vitamin A deficiency can lead to blindness. People who don’t eat enough fruits and vegetables have a higher risk of developing some cancers. So it seemed reasonable for researchers to test whether micronutrient supplements offered the same protective benefits seen in whole foods. Recent data from several large trials proved otherwise.
A trial with the aim of preventing prostate cancer tested vitamin E and selenium in more than 35,000 healthy men. Results showed that men who took vitamin E alone had an increased risk of developing prostate cancer. A trial to test whether vitamin E and beta carotene could prevent lung cancer in 29,000 heavy smokers fared just as poorly. In participants receiving beta-carotene, the incidence of lung cancer increased.
Researchers administer high doses of supplements in clinical trials so they can be assured that those in the supplement group have notably higher nutrient status when compared with those in the control group. But “people confuse the effect of micronutrients in a test tube and the effect of micronutrients in a body,” says Alan Kristal, an epidemiologist at the Fred Hutchinson Cancer Center in Seattle. “They’re really different. It’s taken a while for people to appreciate that.”
Many researchers who specialize in micronutrients are offering a word of caution about micronutrient supplements, even for those who are survivors of cancer. Not only can they be expensive, but the Food and Drug Administration does not regulate supplements, and recent trials proved some supplements harmful. “I always have trouble with this because it’s so important for people to make their own choices, choose their own path and empower their own health. I don’t want to step on that but I don’t take vitamins, and I think it would be better if all cancer patients didn’t either,” says Tim Byers, a clinician and cancer epidemiologist at the University of Colorado in Aurora.
One large micronutrient prevention trial currently underway in the U.S. is testing whether vitamin D and omega-3 fatty acid might prevent colon cancer and heart disease. Vitamin D supplementation has been controversial because experts don’t agree about the health consequences of low vitamin D or whether low levels raise cancer risk or simply serve to identify people who are at higher risk due to other factors associated with low vitamin D.
“In the end it’s like Mom and apple pie,” Kristal says. “After decades, and after hundreds of millions of dollars of research, we discover you should eat an apple every day.”