[英语阅读]维生素补充剂让你更健康吗

在拉丁文里，vita的意思是生命。不少人每天服用各种维生素补充剂，认为这样就可以保持健康。仅仅美国一个国家每年在维生素补充药品上就会扔下几十亿美元——这到底是健康投资，还是花银子打水漂？

The best way to get vitamins is through food, not vitamin pills, according to Susan Taylor Mayne, a professor at the Yale School of Public Health's Division of Chronic Disease Epidemiology. A major problem with supplements is that they deliver vitamins out of context, she says. The vitamins found in fruit, vegetables and other foods come with thousands of other phytochemicals, or plant nutrients that are not essential for life but may protect against cancer, cardiovascular （心脏血管的）disease, Alzheimer's disease and other chronic ailments. Carotenoids（类胡萝卜素） in carrots and tomatoes, isothiocyanates in broccoli and cabbage, and flavonoids（类黄酮）in soy, cocoa and red wine are just a few examples. The combined effect of all these vitamins and phytochemicals seems to have much greater power than one nutrient taken alone.

A healthy diet is paramount, but is there ever a time for supplements? Meir Stampfer, professor of nutrition and epidemiology at the Harvard School of Public Health in Boston, recommends that healthy adults take a multivitamin and extra vitamin D, if they don't get a lot of sun. Taking more than the Institute of Medicine's recommended daily allowance (RDA) of certain vitamins may lower one's risk for certain chronic diseases, he says.

Mayne disagrees, pointing to a recent meta-analysis suggesting that vitamin E supplementation increases mortality of all causes. "We can debate" whether this analysis shows that vitamin E supplements are harmful, she says, but "there certainly wasn't any benefit shown." With the possible exception of vitamin D, there is no need to consume more than the RDA of vitamins, Mayne contends. In fact, there is increasing evidence that excessive intake of certain micronutrients is deleterious.

Stampfer acknowledges that overdosing on certain vitamins can be dangerous. "The most common one to look out for is preformed… vitamin A. It does not take too much to get too much," he says. Try to avoid retinol, retinyl palmitate and retinyl acetate, which may increase the risk of hip fracture and certain birth defects when taken at levels exceeding 10,000 IUs.

But Mayne and Stampfer both agree that more randomized clinical trials are needed to determine the health effects of vitamin supplements—and that such supplements are critical for certain people. Ironically, "the people who are most likely to take vitamin supplements are the people who least need them," Mayne says. The affluent and health conscious are popping supplements faster than anyone. It may not be doing any good, and it could be harming them, she says. Anding concurs: "If you eat well, you probably don't need a multivitamin."