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Safety of Multivitamins Questioned

High levels of folic acid may be harmful

March 3, 2008

• 'Natural' Products Can Be Dangerous for Seniors • Antioxidant Users Don't Live Longer, Study Finds • Safety of Multivitamins Questioned • Vitamin Supplements May Increase Cancer Risk, Report Warns • Cancer Warning Urged for Beta-Carotene Supplements • Researchers Find Some "Health" Supplements Risky • Vitamin B May Harm, Not Help, Heart Patients • Vitamin Supplements May Increase Cancer Risk --- • More about Nutrition ...

The use of some vitamin supplements can be controversial, with scientists and manufacturers arguing over their usefulness. But they don't spend much time arguing about the lowly and somewhat boring multivitamin.

No one has ever argued that multivitamins might not be good for you. Until now.

The Harvard Men's Health Watch, which once endorsed these popular supplements, now says that a reappraisal of that advice is in order.

The publication, in its March 2008 issue, notes that some recent studies have linked multivitamin use to prostate cancer. More convincingly, it says studies have linked high intakes of folic acid to colon polyps, the precursors of colorectal cancer.

Researchers speculate that high intakes of folic acid, which was first added to grain products in the 1990s, may have contributed to an increase in colorectal cancers in the mid-1990s.

What does all of this have to do with multivitamins?

Now that folic acid is added to so many grain products, it's easy to see how a healthy diet, combined with a multivitamin, could boost a person's daily intake to 1,000 mcg or more, potentially increasing the risk of colorectal and possibly prostate and breast cancers.

In light of this research, Harvard Men's Health Watch editors suggest that the average man give up the multivitamin, at least until scientists solve the puzzle of folic acid and cancer.

However, if you stop taking a multivitamin, the authors suggest you consider taking a vitamin D supplement. The typical diet for most men and women doesn't supply enough of this crucial vitamin, and while sun exposure boosts vitamin D production, it has health risks of its own.

Last month, a study suggested some multivitamins might increase cancer risk.

"Our study of supplemental multivitamins, vitamin C, vitamin E and folate did not show any evidence for a decreased risk of lung cancer," wrote the study's author, Christopher G. Slatore, M.D., of the University of Washington, in Seattle. "Indeed, increasing intake of supplemental vitamin E was associated with a slightly increased risk of lung cancer."

Findings of the study of 77,000 vitamin users were published in the first issue for March of the American Thoracic Society's American Journal of Respiratory and Critical Care Medicine.

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