Multivitamins may slightly reduce the risk of cancer but don’t prevent heart disease. Keep the focus on diet, not supplements.
Up to half of all adults in the United States may already take a multivitamin. Most probably expect it to make them feel better and prevent common illnesses, even though the evidence has always been a little sketchy. Is the one-a-day multivitamin habit truly healthful—or just wishful thinking?
The Harvard-led Physicians Health Study II (PHS II) recently found that taking a multivitamin slightly lowers the risk of being diagnosed with cancer. But if you take a multivitamin already or plan to, don’t let it distract you from eating a varied and nutritious diet. “The studies of taking vitamins to prevent disease have been largely disappointing,” says Dr. William Kormos, editor in chief of Harvard Men’s Health Watch and a primary care physician at Harvard-affiliated Massachusetts General Hospital. “It does not appear that a multivitamin can replace a healthy diet high in fruits and vegetables.”
Multivitamins lower cancer risk by 8%
Study II, involving about 15,000 doctors, looked at the effect of multivitamins on disease risk. Here are the results per 1,000 men.
Result: 13 fewer men were diagnosed with cancer because they took a multivitamin—an 8% reduction in cancer diagnosis, but not in death.
Putting multivitamins to the test
Many studies have looked at the effect of vitamin and mineral supplements on disease, but the evidence has never been convincing. So most experts have hedged on whether to recommend multivitamins for everyone.
The PHS II study involved nearly 15,000 physicians. Half were chosen at random to take a daily multivitamin; the others received a placebo pill containing no vitamins or minerals. The men took their pills for an average of just over 11 years. At the end of the study, researchers determined who developed cancer or heart disease and how many died from those diseases, which account for roughly half of all U.S. deaths annually.
The PHS II was the first study to test a standard multivitamin for the prevention of chronic disease. “All the other studies were done with a single supplement, or combinations of two or three, usually at higher levels than you could get from your diet,” explains Dr. J. Michael Gaziano, a cardiologist at Harvard-affiliated Brigham and Women’s Hospital and VA Boston Healthcare, and one of the leaders of the PHS II study.
The cardiovascular disease portion of the study focused on whether taking a multivitamin reduced the risk of heart attacks, strokes, and death from cardiovascular disease. There was no effect, weakening the case for taking a multivitamin “just in case” to prevent heart disease.
However, PHS II did find that taking a supplement reduced the risk of being diagnosed with a new cancer by 8%. The trial found indications that the multivitamin might reduce death from cancer, too, but the effect was weak and could have been due to chance.
If you don’t take a multivitamin now, should you do so based on the PHS II -findings? Dr. Gaziano thinks it’s a reasonable choice. The cost of multivitamins is negligible for most people—less than a dime a day if you buy no-name brands in bulk at a large discount chain. And PHS II found no reason to believe that taking a multivitamin is dangerous. Moreover, “taking a multivitamin to prevent deficiency is not a bad idea,” Dr. Gaziano says. “Many Americans don’t get what they need.”
As for cancer prevention, he argues, the supplement offers a new option to an aging population at high risk of developing cancer at some point in their lives. “Until now, the only things proven to prevent cancer were stopping smoking and never starting,” Dr. Gaziano says. “Now we know that multivitamins provide a modest benefit.”
Vitamin and mineral supplements: Too much of a good thing can make you sick
When it comes to vitamins and minerals, some people subscribe to the notion that if a little is good, then more is better. But nutrients can be harmful when taken in amounts above what’s considered beneficial.
Determining the right amount is tricky, however. Each nutrient has a range that starts with the minimum daily intake level necessary to meet the needs of most healthy people, called the Recommended Dietary Allowance (RDA). The top of the range is given as the tolerable upper intake level (UL) of the nutrient. The amount right for you must be based on your needs, so talk to your doctor before you start taking new vitamin and mineral supplements.
“Exceeding the RDA is not a medical problem essentially until the UL is reached, and then it can become harmful,” explains Dr. Bruce Bistrian, chief of clinical nutrition at Beth Israel Deaconess Medical Center and professor of medicine at Harvard Medical School.
Benefits for all?
But it is difficult to know from the PHS II study what ultimate benefit a multivitamin would provide for the general population. Compared with most people, the doctors in the study ate better diets, were more physically active, and engaged in fewer unhealthy activities. Less than 4% were smokers, and 60% exercised at least once a week. In contrast, American men on average are overweight, don’t exercise as much as they should, and take in too much fat and sodium. Would a multivitamin help them, too?
One could argue that if something helps healthy people a little, it should help less healthy people more. But it’s also possible that the modest anti-cancer benefit of taking multivitamins wouldn’t make much of a dent, compared with the effect of less healthy lifestyles in the general population. Don’t expect to see a massive new clinical trial to answer that question anytime soon.
Dr. Gaziano takes the optimistic view: “If you consider even a modest reduction in risk for a disease as common as cancer in the population at large, it’s not trivial numbers that you’re talking about.”
A multivitamin for you?
Still, it’s important not to overplay the benefit that PHS II found for preventing cancer. “The effect in this study is relatively small,” Dr. Kormos says. Rather than relying on supplements, it’s a better to obtain nutrients from food, which contains a variety of healthful ingredients.
Fruits and vegetables contain many biologically active ingredients that may help to prevent cancer in ways that vitamins and minerals alone do not. “A healthy diet still seems superior to taking a multivitamin, and if you already eat a healthy diet, there may be less overall benefit from taking the extra vitamins,” Dr. Kormos says. You’ll hear similar advice from the American Cancer Society and the American Heart Association.
In considering the pros and cons of multivitamins, stop for a moment and ask what you expect to gain and why you think you need a supplement to begin with. “If people ask me if they should take a multivitamin, I usually ask, Why do you think you need one?” Dr. Kormos says. “They say, well, I don’t eat this, I don’t eat that. But a multivitamin is not going to replace the things missing from your diet. Whatever money you are spending on your multivitamin, it’s probably better to spend it at the farmer’s market or the grocery store on healthy foods.”