Can multivitamins protect you from cancer?

What the best study so far shows.


“For a lot of people, multivitamins add an extra layer of security to ensure they’re getting at least minimum levels of essential vitamins and minerals to avoid nutritional deficiency or insufficiency, ” says Howard Sesso, associate professor of epidemiology at the Harvard T.H. Chan School of Public Health in Boston.

But can a multi also prevent disease, like cancer or heart disease? That remains an open question.


The longest, largest controlled study so far

In the Physicians’ Health Study II, Sesso and his colleagues randomly assigned more than 14,000 men aged 50 and older to take a daily Centrum Silver (one of the most popular basic multivitamin-and-minerals for seniors) or a placebo.

After 11 years, the multi takers had an 8 percent lower risk of being diagnosed with cancer (and a 9 percent lower risk of cataracts) than the placebo takers. “And among men who had a history of cancer at the start of the trial, results suggested that the multivitamin was even stronger in preventing new cancers,” adds Sesso.

However, the multi takers were just as likely to have heart attacks or strokes, to suffer memory loss or other cognitive decline, or to die during the study. (Centrum had no role in conducting the study or interpreting the results.)


But questions remain.

“We don’t know whether the lower cancer risk found in men extends to women, or whether taking a multivitamin has stronger benefits in those with a history of cancer,” says Sesso.

COSMOS, a new clinical trial on women aged 65 or older and men aged 60 or older, should provide some answers by 2020. (Interested in participating? Visit www.cosmostrial.org or call 800-633-6913.)

Until then, says Sesso, “we hope to fill in some of these research gaps with observational studies.”


Observational studies provide clues

Unlike a clinical trial, observational studies look at the risk of disease among people who do or don’t choose to take a multi on their own.

For example, the Nurses’ Health Study II has tracked more than 43,000 women since 1989. Those who took multivitamins were less likely to have precancerous colon polyps and less likely to be infertile because of ovulation problems.

“The challenge in looking at observational studies is that people who take multivitamins differ from those who don’t,” says Sesso. “While observational studies try their best to account for the differences—like smoking and exercise—they can’t adjust for differences they don’t know about.”

Then there’s the question of what people take. “We don’t know if all multivitamin formulations have similar effects, or whether particular combinations of vitamins and minerals are better than others,” says Sesso.


Could multis be harmful?

A 2011 observational study of Iowa women rattled some people when it found that multi takers were slightly more likely to die than non-multi takers. But the result appears to be a fluke. Other observational studies and clinical trials don’t find a higher risk of dying among those taking a multi.

“There doesn’t appear to be any harm from taking ordinary big-brand multivitamins,” says Sesso. “But whether they can prevent disease remains a work in progress.”

Skip the specialized formulations that add herbs or other botanicals, says Sesso. “We don’t really know how these ingredients interact and what their long-term effects are.”


Sources: JAMA 308: 1871, 2012; Ophthalmology 121: 525, 2014; JAMA 308: 1751, 2012; Ann. Intern. Med. 159: 806, 2013; Br. J. Cancer 110: 249, 2014; Fertil. Steril. 89: 668, 2008; Arch. Intern. Med. 171: 1625, 2011; Am. J. Epidemiol. 173: 906, 2011; Am. J. Clin. Nutr. 97: 437, 2013.

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