Do multivitamins inoculate you against cancer?

By Justin Matlick, Hutchinson Center science writer

You can’t blame somebody for wanting a silver bullet to protect them from cancer. And this desire may partly help explain why Americans spend upwards of $20 billion a year on vitamins and supplements.

After all, we know that eating a diet heavy in fruits and vegetables plays a big role in reducing cancer risk. And it seems reasonable to assume that vitamins in these foods are the ingredients behind this preventative effect, and that consuming them via pills or supplements will protect against the disease. The problem is, researchers can’t confirm that vitamins—or any other particular ingredients—account for the reduced risk.

“There must be something in the foods that’s doing this, but it’s been hard to isolate exactly what it is,” says the Hutchinson Center’s Dr. Emily White. “It might be a vitamin, or a mineral, or a range of nutrients from different foods that work together in a way you can’t replicate in a pill.”

Dr. Emily White

Continued research may shed more light on role of vitamins and other supplements

White has spent several years tracking how 38 different supplements impact the health of more than 75,000 study participants. Her goal is to see if people who take certain supplements are diagnosed with cancer more or less frequently than people who don’t take them.

So far, some of the strongest findings have centered on multivitamins. The bottom line?  “In general, there’s no strong evidence that taking a multivitamin increases or decreases your cancer risk,” White says.

Another Hutchinson Center study reached a similar, if more gender-focused, conclusion. Led by Dr. Marian Neuhouser and published in 2009, the study looked at multivitamin use among 161,000 women and found that taking multivitamins did not affect the likelihood of contracting cancer or cardiovascular disease.

Dr. Marian Neuhouser

But what about more specific vitamins? After all, the world is awash in claims that particular supplements, ranging from vitamin D to fish oil, can prevent particular cancers. While White says there’s a lot of work left to be done in this area, she pointed to a number of studies that have started testing some of the most common claims:

• After preliminary research suggested that vitamin E and selenium could help prevent prostate cancer, Hutchinson Center researchers contributed to a 2008 study, published in the Journal of the American Medical Association, finding that these supplements had no impact on prostate cancer risk.
• Carrots and their component beta carotene have also been said to decrease prostate cancer risk. But, after conducting clinical trials of beta carotene and retinyl palmate, a research team that included Neuhouser and the Hutchinson Center’s Dr. Alan Kristal and Matt Barnett found that these supplements do not prevent prostate cancer. In fact, the evidence suggests that taking these supplements in high doses may increase the risk of contracting the disease.
  

  Dr. Alan Kristal

• Vitamin D supplements are often pegged as a way to stave off colorectal cancer. However, our Dr. Andrea LaCroix led a study of 36,000 postmenopausal women showing that calcium and vitamin D supplements did not impact incidence of the disease.

Research focuses on fish oil

Of course, this is only the beginning. With hundreds of supplements on the market, there may be some that have anti-cancer effects. Researchers here and elsewhere are doing their best to identify these; a Harvard University team, for instance, recently launched a randomized trial studying the health effects of fish oil, a supplement of interest to White.

Last year, she published a study that found high levels of the omega-3 fatty acids EPA and DHA were associated with a 32 percent reduction in breast cancer risk. However, she cautioned against gleaning any recommendations from the results of one study.

Until scientists can establish a clearer link between supplements and cancer, White has some simple advice for consumers tempted by the pills and powders beckoning from the health food aisle. “You should be shopping in the produce section instead,” she says.