Should you keep taking that multivitamin?

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The news about vitamins keeps getting worse.

A spate of high-profile studies published in the last few years showed that a variety of popular supplements -– including calcium, selenium and vitamins A, C and E –- didn’t do anything to reduce the risk of developing heart disease, stroke or a variety of cancers. (A roundup on the studies can be found here.)

But what about multivitamins? These combination pills, which contain 10 to 30 vitamins and minerals, are the most popular dietary supplements sold in America. A report published today in the Archives of Internal Medicine suggests they shouldn’t be.

The study tracked 161,808 participants in the Women’s Health Initiative, a long-term effort to identify risk factors for cancer, heart disease and bone health among postmenopausal women. Subjects hailed from all over the country and included white, black, Latina, Asian and Native American women. They were followed for an average of nearly eight years.

Overall, 41.5% of study participants took some version of a multivitamin. Those women were more likely to be white and college-educated, live in the West, exercise and have a lower body mass index.

However, they weren’t any more likely to ward off a diagnosis of breast, ovarian, lung, stomach, bladder, kidney, colorectal or endometrial cancer compared with women who didn’t take multivitamins. Nor were the pills helpful in preventing heart attacks, strokes, blood clots or the risk of death from any cause during the study period.

The research team, led by scientists at the Fred Hutchinson Cancer Research Center in Seattle, did find one modest benefit: The 3,741 women who took stress multivitamins –- formulations with higher doses of several B vitamins along with an extra jolt of vitamin C -– were 25% less likely to have a heart attack. No other correlations between vitamins and health outcomes were statistically significant.

The study provides “convincing evidence that multivitamin use has little or no influence on the risk of common cancers, [cardiovascular disease], or total mortality in postmenopausal women,” the authors wrote.

So, they wondered, “Why do millions of Americans use a daily multivitamin for chronic disease prevention when the supporting scientific data are weak?”

Some physicians continue to recommend them as a backstop for patients whose diets may contain nutritional gaps. And since they don’t require a prescription, many people simply assume they are safe.

But those assumptions may not be warranted, especially if people wind up overdosing on vitamins and minerals, the researchers wrote. They suggested it may be time to settle the question once and for all by investing in a large-scale randomized controlled trial, the gold standard of medical research.

-- Karen Kaplan