Two large well-designed studies published in the 1/7/2009 issue of the Journal of the American Medical Association (JAMA) showed that regularly taking selenium and vitamins C and/or E supplements did not help prevent cancer. As reported by Liz Szabo in USA Today, these and other studies demonstrate that “Vitamins Get ‘F’ in Cancer Prevention.” As an added bonus, the article has a nice table that summarizes findings from recent studies testing the value of vitamins in preventing certain cancers and heart disease. Szabo writes,
A flotilla of recent studies — including two papers published today — has sunk the notion that individual vitamin supplements prevent cancer. With so many earlier studies suggesting that people can eat their way to longer lives, experts acknowledge that their latest findings may leave people confused and even frustrated.
“A lot of people are looking at this and asking, ‘What happened?’ ” says Lori Minasian, whose study in today’s Journal of the American Medical Association found that taking vitamin E or selenium does not ward off cancer. But researchers also say that diet is one of the most difficult areas to study. Unlike lab rats, after all, no one eats one thing all the time.
“Cancer is complex and the interaction of nutrients is complex, so put the two together and you’ve got a lot of really tough scientific questions to answer,” says the American Cancer Society’s Colleen Doyle.
Researchers have noted for years that populations with healthy diets — lots of vegetables, little junk food — are less likely than others to get cancer, says Peter Gann of the University of Illinois-Chicago, who wrote an editorial accompanying the new papers. It’s been much more challenging to tease out the specific foods — or even compounds — that keep cells from turning malignant, Gann says. Is it the fish oil? The soy? The lack of red meat? Experts also note that the specific dose of a vitamin may be critical.
People who get too little of a nutrient may be at greater risk of cancer, but so may those who get too much, Minasian says. Given the popularity of vitamins and other supplements, she says it’s important for researchers to find the right combination. Other experts, such as Gann, say that it may be time for researchers to abandon the idea of using individual vitamins to prevent cancer.
Instead, he says, health-conscious consumers should focus on getting their vitamins from plant foods, such as vegetables and whole grains, which contain precise mixtures of hundreds or even thousands of compounds. Many of these compounds may work better in the combinations selected by nature. Doyle says there are still lots of proven ways, in addition to a plant-based diet, to reduce the risk of cancer: Exercise, maintain a healthy weight and avoid tobacco. Screenings for colon cancer, cervical cancer and breast cancer also have been shown to save lives. [...]
Szabo has also written a very helpful “Q&A: Which Studies Are Worth Attention?” which explains to consumers how to evaluate research on diet. Here are a couple of excerpts from this Q&A, which I think should be required reading for people considering the use of dietary supplements for cancer prevention.
Q. Why do the new studies contradict the findings of earlier research?
A. Many of those earlier studies were preliminary. That means they usually can’t prove cause and effect, Gaziano says. Scientists are familiar with these limitations. “Conflicting results are part and parcel of the scientific process,” Gaziano says. “It’s why we’re often reluctant to make a clinical recommendation based on a single result.” But consumers — who pay much closer attention to diet news than to other areas of medicine — can easily get confused if they mistake these early findings for solid results, says Peter Gann of the University of Illinois at Chicago, who wrote an editorial accompanying Gaziano’s studies in The Journal of the American Medical Association.
Q. So which studies should we pay attention to?
A. The strongest studies are called randomized clinical trials. These are the best experiments for proving that one thing causes another, Gaziano says. In these tests, researchers randomly assign one group of people to do one thing, such as take a vitamin, but assign a comparison group to do something else, such as take a placebo pill, he says. In a “double-blind trial” — the most rigorous kind — neither patients nor their immediate doctors know which pills they’re taking. Only the researchers running the trial know who’s in which group. An outside panel oversees the study to make sure that patients aren’t harmed and may stop the study early if problems surface.
Q. What’s the best way to research a health study?
A. Because all drugs — including vitamins and herbs — have side effects, it’s worth taking the time to do some research putting them in your body, Gaziano says. Gaziano suggests that consumers read news stories carefully to assess how doctors got their results. If a story isn’t clear, patients should consider looking up the original article in a medical journal or asking their doctors. Patients can also consult the websites of major medical organizations, such as the American Cancer Society,the Centers for Disease Control and Prevention or the National Cancer Institute. These groups sift through scientific evidence when making recommendations about diet, screening tests and other health issues.
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