Taking Vitamins to Prevent Cancer or Heart Disease

In my practice we ask our patients to bring all of the medications they are taking, including vitamins and herbs or supplements, to every office visit. This is so that if a patient is seeing more than one doctor - maybe a cardiologist in addition to visiting me, an internist - we can make sure that none of the medications they are taking will interact with each other in negative ways. (Coumadin (warfarin) users should be especially careful to do this, as many medications, vitamins, or supplements will intact with the warfarin, sometimes with serious consequences.) I discourage my patients from taking most vitamins, as the research is fairly clear that for those who are not nutrient deficient or need supplementation for some other reason (like being vegan or pregnant), getting your vitamins from foods and not pills is better for you. (Here's more discussion and citations.)

That said, in research it is important that a study not only be well-designed, its results must also be verifiable by others performing a similar trial and getting similar results. This is why in looking at how strong the evidence is for one thing or another, we do what is known as a "review." A review of all of the relevant, well-performed studies performed on a particular topic helps us see whether certain results or conclusions are consistent: if they are not, then we can't say that something is "proven."

Recently a team of researchers reviewed the current state of the evidence regarding vitamin and mineral supplements, choosing to focus on their effect, if any, on the risk of heart disease or cancer (Ann Intern Med 2013;159(12):824-834). In choosing the relevant trials, they limited themselves to those studies published between 2005 and early 2013, looking at the following vitamins and minerals (or combinations thereof): A, B1, B2, B6, B12, C, D, E, calcium, iron, zinc, magnesium, niacin, folic acid, beta-carotene, and selenium. After identifying all of the possible articles, the further limited themselves to those studies that were considered of "good" or "fair" quality as defined by the U.S. Preventive Services Task Force (USPSTF). Finally, all of the included studies were on people who were had no known nutrient deficiencies, leaving the researchers with a total of 26 studies.

The findings of all of the included studies were not only mixed, but often contradictory. For example, two studies of multivitamins (a combination of three or more vitamins and minerals) found lower cancer incidence in men of nearly clinical significance, but in another study that also included women, no such effect was found. The original investigators of the first two studies speculated that this effect was because men generally have lower antioxidant levels than women.

When the researchers assessed the studies for any harm done by taking the vitamins or minerals, they found similar, mixed if not outright contradictory, results. One interesting exception was taking beta-carotene: it appeared to increase the risk of lung cancer in those already at higher risk for lung cancer, such as smokers or those who work with asbestos. Another firm result was that taking vitamin E consistently showed no effect on the risk of heart disease or cancer.

What this means for you

Don't bother taking vitamin E and definitely avoid taking beta-carotene if you smoke. And even those conclusions could change in light of further research. Right now we don't have good evidence supporting taking vitamins unless your doctor has told you to, so why waste your money? Better to spend that money on great quality food - it's much more tasty than taking pills and we know it's more effective.

First posted: November 13, 2013