The supplements industry has little doubt about what message you should take away from a recent flurry of research-related headlines about the health effects of multivitamins. The ink was hardly dry on one report in JAMA before television commercials began touting the apparent cancer-fighting benefits of a daily multivitamin. A spokesman for a dietary-supplements trade association exulted that a new study “pushes the door and the windows wide open to the benefits and safety of multivitamins.”
But Joel B. Mason, MD, a professor of nutrition and medicine at Tufts and director of the HNRCA Vitamins and Carcinogenesis Laboratory, is more cautious in his take on the latest findings. “There is pretty compelling evidence that an inadequacy of certain nutrients or habitual underconsumption does lead to increased cancer risk,” he says. “In America, however, most people achieve adequate levels of these cancer-fighting micronutrients.”
Moreover, Dr. Mason cautions, just as too little of some vitamins and minerals can be harmful to your health, so can too much. The scientific literature is stud-ded with disappointing, even dangerous results of trials of supplements that backfired. Smokers who were administered high doses of beta carotene, for example, in hopes of reducing their lung-cancer risk actually developed more cancers than those given a placebo. In 2009, the National Cancer Institute (NCI) prematurely halted a major trial of selenium and vitamin Es possible benefits against prostate cancer; men in the vitamin E group had a statistically nonsignificant increased risk of prostate cancer, and those assigned to selenium pills had a slightly raised risk of type 2 diabetes.
Even in studies where no such downside was reported, Dr. Mason says, Taking more of many vitamins and minerals, beyond whats needed to insure adequacy, doesnt seem to further reduce health risks.
THE GOLDILOCKS PHENOMENON: Dr. Mason believes there may be a Goldilocks phenomenon in the health effects of certain vitamins and other nutrients. Like Goldilocks seeking porridge thats just right in temperature, the body may benefit most from doses of vitamins and minerals within a specific optimal range. Too much or too little can miss that Goldilocks range and the associated health benefits.
Take folate, for ex-ample. I think there is a pretty compelling case that habitual underconsumption of folate does lead to an increase in colon cancer, and perhaps a few other types of cancer as well, Dr. Mason explains. Folate is an essential factor in the synthesis and repair of DNA. But supplementing folate in a generally well-nourished population does not seem to reduce cancer risk. In fact, there are concerns that some people who take extremely high amounts of folate may actually see a paradoxical increase in colorectal cancer.
So when you consider the claims of multivitamin marketers, it might also make sense to weigh the nutritional quality of your own diet. If youre already eating a balanced diet, especially one rich in the fruits and vegetables that contain many of the nutrients supplemented by multivitamin pills, more vitamins and minerals in the form of a multivitamin might not do you much good. And if your diet is falling short, experts advise that your first step in fixing the problem should be to improve your dietary intakes.
Even the researchers reporting that daily multivitamin use was associated with a small but significant decrease in cancer risk among a group of older male physicians caution against viewing the pills as a magic bullet. J. Michael Gaziano, MD, of Brigham and Womens Hospital in Boston, warned, It would be a big mistake for people to go out and take a multivitamin instead of quitting smoking or doing other things that we have a higher suspicion play a bigger role, like eating a good diet and getting exercise. He added, Youve got to keep wearing your sunscreen.
COMBATING CANCER? Dr. Gaziano and colleagues reported results from the Phy-sicians Health Study II, involving 14,461 male physicians. In the multivitamin arm of the study, men were randomly assigned to take either a daily, commercially available multivitamin formulated for older people, or a placebo. Participants had an average age of 64.3 and 1,312 had a prior history of cancer when the study began.
Over 14 years of follow-up, 2,669 of the men had confirmed cancer diagnoses. Prostate cancer accounted for slightly more than half of those cancer cases, with colorectal cancer the second most common type.
Looking at all cancers, men ran-domly assigned to a daily multivitamin were at 8% lower risk. Excluding pros-tate cancer-where risk did not differ significantly with multivitamin use-the risk of all other cancers was 12% lower in the multivitamin group. Cancer mortality was also 12% less in those taking multivitamins, though that difference did not achieve statistical significance. Among men with a history of cancer, those in the multivitamin group were 27% less likely to develop another cancer than their peers assigned to the placebo group.
Previous studies looking for a benefit against cancer or other diseases from multivitamins have mostly been disappoint-ing. A 2006 review by the National Institutes of Health-which also supported the new study-concluded that evidence was insufficient to prove the presence or absence of benefits from use of multivitamins and mineral supplements. The 2010 Dietary Guidelines for Americans similarly cautioned that there is no evidence supporting taking a multivitamin to prevent chronic disease. The American Cancer Society recommends eating a healthy diet, and that those who also take a multivitamin choose one containing no more than 100% of the daily value (DV) of most nutrients. Nonetheless, its estimated that about one-third of all American adults take a multivitamin.
STRENGTHS AND WEAKNESSES: The latest study, published in JAMA and unveiled at a national cancer conference, may be different, researchers say-and not just because the findings were more encouraging. Most prior research on multivitamins and chronic disease relied on observational studies. The Physicians Health Study II is a randomized, controlled clinical trial, considered the gold standard of scientific research.
Moreover, by focusing on multivitamins rather than individual nutrients, the study may have avoided the pitfalls of previous single-nutrient trials. In comments at the cancer conference, co-investigator Howard Sesso, ScD, also of Brigham and Womens Hospital and Harvard Medical School, said, We dont know exactly how it works, and I think thats the point. If you look at all the previous large-scale trials on individual vitamin supplements and minerals, those were based on megadoses of a specific vitamin or mineral. Because they were testing one thing, they provided a very clear answer.
A multivitamin is a much more broad-based approach. We were looking at lower levels, sort of the usual intake of a whole range of vitamins and minerals together in combination. Its our feeling that its more the combination of the vita-mins and minerals working together that might be responsible for the effect, more so than any specific component.
Despite the strengths of the study, other experts also pointed out some weaknesses. Most obviously, the participants were all men, so its unclear whether the results would also apply to women. The male physicians, who were unusually diligent in taking their daily pills, were also more healthy than typical for their age and had extremely low smoking rates.
Commenting on the results, Marji McCullough, ScD, RD, a nutritional epidemiologist with the American Cancer Society, said, We still need to find out whether these findings can be applied to others in the population.… Its worth trying to replicate these findings to see if theyre generalizable to women, smokers and others.
NO HEART BENEFIT: Just weeks after the cancer findings were released, moreover, the same researchers reported results about multivitamin use and heart disease that youre much less likely to hear about in TV commercials. In further findings from the Physicians Health Study II, Sesso and colleagues found no improvement in cardiovascular risk associated with a daily multivitamin.
There was no difference between the multivitamin group and those taking a placebo in risk of heart attack, stroke or cardiovascular death. Nor did the multivitamin users see any benefit in either primary or secondary prevention of cardiovascular disease.
The heart study evaluated an average of 11.2 years of followup in the same group of male physicians. Results were announced at a meeting of the American Heart Association and also published in JAMA.
Cardiologists commenting on the findings at the conference emphasized that patients should not take multivitamins as a substitute for more proven lifestyle modifications, such as eating a healthy diet or quitting smoking. Nor can multivitamins take the place of medications such as antihypertensive or statin drugs.
Sesso agreed, saying, “Many people take vitamin supplements as a crutch. Theyre no substitute for a heart-healthy diet, exercising, not smoking, keeping your weight down.”