Alphabet overload: Which dietary supplements are effective?

Despite an array of vitamin supplements on the market, evidence of the benefits of all but a few remains inconclusive.

By Susan J. Landers, AMNews staff. Sept. 6, 2004.

From vitamin A to zinc, supplements line supermarket and drug store shelves in a mind-numbing proliferation of strengths and configurations. Health claims on labels stay narrowly within legal boundaries -- catching the eye and raising the hopes of unwary consumers.

At least a third of the population takes a vitamin and mineral supplement every day, according to a recent federal survey. And sales in the United States reached $6.6 billion in 2003, a 7% growth over the year before, with about half spent on multivitamins and B vitamins as well as C and E. But which of these, if any, should be taken is a puzzle for patients and for their physicians.

Adding to the problem is that some patients aren't forthcoming about the supplements they are taking, unaware that harmful interactions with some medications and some conditions can occur.

A recent clinical trial, for instance, linked beta-carotene supplements with higher rates of lung cancer in heavy smokers. Another trial found that vitamin E can cause increased bleeding, especially among people already taking anticlotting medication.

Then there's the question of proper dosing, because large amounts can sometimes be counterproductive.

It's not difficult to get too much vitamin A, said Meir Stampfer, MD, DrPH, chair of the Harvard School of Public Health's epidemiology department. "Between supplements, fortified breakfast cereals and milk, it's easy to get up to 10,000 or more international units per day, and that's a level where you start to see clinical harm in terms of increased susceptibility to fractures and other adverse health effects."