Dr. Oz: How Excess Vitamins Can Harm

As a longtime champion of the multivitamin, I'm intrigued by two new studies that suggest certain vitamins found in a multi might do more harm than good.

The first study, in Iowa, found that older women who used multivitamins and other supplements had a slight overall increased risk of dying. A second study suggested that men who took high doses of vitamin E had a 17 percent increased risk of prostate cancer after seven years.

Both studies provide valuable lessons but invite appropriate criticism, too. A previous study found none of the multivitamin risks cited in the Iowa study. Most important, though, is that much of the death risk in the Iowa study was specifically linked to iron supplementation.

Iron is one of those tricky multivitamin components. If you're a premenopausal woman, it can help offset iron loss caused by menstruation. After menopause, however, excess iron can become dangerous. Iron is an oxidant, which means it can trigger cellular damage.

In the prostate cancer study, the participants in the vitamin E group were taking 400 international units (IU) a day for several years, even though the recommended daily allowance of vitamin E is just 22 IU a day. That said, a separate group of men in the study who took both selenium and vitamin E showed no significantly increased risk for prostate cancer. Some argue this difference shows the importance of examining vitamins together, not in isolation, because they may work synergistically to confer health benefits.

So, yes, I still recommend a multivitamin for most people, but read the labels. Look for a multi with no more than 3,500 IU of vitamin A and no more than 30 IU of vitamin E. Medical research supports these values as safe doses that can compensate for dietary insufficiency.

I've never been a fan of megadose multivitamins — those vitamin tablets that contain well in excess of 100 percent of the daily value. So stay away from those. And remember, I recommend iron in a multivitamin only for premenopausal women; otherwise, make sure you choose one without iron.

Finally, maximize the benefits of your multivitamin: Take half in the morning and half at night to ensure your body gets a steady supply of these healthful nutrients.

Remember to go to the AARP home page every day for tips on keeping healthy and sharp, and great deals.