Vitamin Overdose

By Ian K. Smith, M.D.

My mother always told me that too much of a good thing can be bad for you. If I didn't already believe her, last week's bulletin from the Institute of Medicine would have persuaded me. The institute, an arm of the National Academy of Sciences, made headlines last year with an alarming report about how often medical mistakes are made in hospitals. This time it tackles vitamins C and E and other so-called antioxidants, and it warns against ingesting too much of them.

Vitamins are America's favorite supplements; you may be among the 40% who took at least one within the past month. All told, we spend $1.7 billion a year on those pills and capsules--most commonly vitamin C, which originally attracted attention as a supposed cold remedy. But interest in these supplements has been fanned in recent years by hints that antioxidants such as vitamins C and E and selenium soak up free radicals, those by-products of metabolism that can damage cells and have been implicated in a wide variety of diseases, from cancer and cardiovascular disease to Alzheimer's, as well as in aging.

While the optimist in each of us wants these claims to be true, the findings from the task force, led by Tufts University biochemist Norman Krimsky, deliver a sobering dose of reality. There is insufficient scientific evidence, the team concludes, to support the notion that taking megadoses of dietary antioxidants can prevent chronic diseases. But the report goes even further. "Extremely large doses [of antioxidants]," it says, "may lead to health problems." Megadoses of vitamin E, for instance, can put you at greater risk of bleeding, while too much vitamin C causes diarrhea and may interfere with cancer treatments. Take too much selenium, and you can lose hair and even fingernails.

But what exactly constitutes too much? The panel suggested it was safe to increase the recommended daily dose of both vitamins. It recommended 75 mg of vitamin C for women, 90 mg for men. Because smokers are more likely to deplete vitamin C, it suggested they take an additional 35 mg daily. But, it emphasized, no adult should consume more than 2,000 mg of vitamin C a day.

The panel increased the recommended daily intake of vitamin E for both men and women to 15 mg, or 22 IU (international units), if it comes in the form of alpha-tocopherol, which is the only type human blood can store and transfer to cells. For d-alpha-tocopherol, another form of the vitamin, the daily limit is 1,000 mg, or 1,500 IU. For dl-alpha-tocopherol, a synthetic form of vitamin E, the limit is 700 mg, or 1,100 IU. As for selenium, the upper limit is 55 micrograms a day.

Of course, if you eat the way your mom told you to, you may not need to take any supplements. Consuming five servings of fruits and vegetables in the course of a day is often a better way to meet your daily vitamin requirements. It's almost impossible to overdose on such foods unless you're eating truly gargantuan portions. Besides, fruits and vegetables seem to have other, hidden health benefits.

For good sources of vitamin C, look to citrus fruits, potatoes, strawberries, broccoli and leafy green vegetables. Vitamin E is tucked away in nuts, seeds, liver, leafy green vegetables and vegetable oils. You can get selenium from fish, meat, grains and--yes!--garlic. So before you reach into your medicine cabinet for another pill, glance down at your plate first. It probably contains all the antioxidants you need.

For more information on vitamins, visit www.nal.usda.gov/fnic Questions for Dr. Ian? E-mail him at [email protected]