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[未归类] IBT Fact or Fiction?: Vitamin Supplements Improve Your Health [复制链接]

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发表于 2007-5-28 22:20:39 |显示全部楼层
Vita means "life" in Latin, and vitamins are essential for life.The World Health Organization calls them the "magic wands" used by thebody to synthesize enzymes, hormones and other chemical necessities.Unable to create vitamins from scratch, the body must fetch them fromoutside sources—typically food. But do the pills many pop for healthdeliver the same benefits?


Humans need 13 vitamins to survive. Vitamins, also called"micronutrients" because they are required in minute quantities, can begrouped in two categories. There are those that dissolve in fat—A, D, Eand K—and can accumulate in the body when consumed in excess. And thereare those that are water soluble—C and B—which are easily excreted, asanyone who takes large quantities of vitamin C and riboflavin (B2) cantestify. (Their urine is bright yellow or orange.)
                                                                                               
The best way to get vitamins is through food, not vitaminpills, according to Susan Taylor Mayne, a professor at the Yale Schoolof Public Health's Division of Chronic Disease Epidemiology. A majorproblem with supplements is that they deliver vitamins out of context,she says. The vitamins found in fruit, vegetables and other foods comewith thousands of other phytochemicals, or plant nutrients that are notessential for life but may protect against cancer, cardiovasculardisease, Alzheimer's disease and other chronic ailments. Carotenoids incarrots and tomatoes, isothiocyanates in broccoli and cabbage, andflavonoids in soy, cocoa and red wine are just a few examples.


The combined effect of all these vitamins and phytochemicals seemsto have much greater power than one nutrient taken alone, Mayneexplains. For example, lycopene—the carotenoid that gives tomatoestheir red hue—has been associated with a lower risk for prostatecancer, causing many supplement makers to rush to market pills bearingthis healthy stuff. But research suggests that taking it in supplementform does not confer the same benefit as eating tomatoes or tomatoproducts, such as pasta sauce and ketchup, that preserve some of thetomatos chemical integrity.

A healthy diet is paramount, but is there ever a time forsupplements? Meir Stampfer, professor of nutrition and epidemiology atthe Harvard School of Public Health in Boston, recommends that healthyadults take a multivitamin and extra vitamin D, if they don't get a lotof sun. Taking more than the Institute of Medicine's recommended dailyallowance (RDA) of certain vitamins may lower one's risk for certainchronic diseases, he says. For example, Stampfer's research suggeststhat men and women taking vitamin E supplements for years at a timehave a lower risk for heart disease. "The evidence for benefit isweak," but there is also "good evidence for no harm" associated withtaking 200, 400, or even 600 IUs (international units) per day,Stampfer explains. (The RDA levels for vitamin E are 22.5 IUs, or 15milligrams, for men and women.)

Mayne disagrees, pointing to a recent meta-analysis suggesting thatvitamin E supplementation increases mortality of all causes. "We candebate" whether this analysis shows that vitamin E supplements areharmful, she says, but "there certainly wasn't any benefit shown." Withthe possible exception of vitamin D, there is no need to consume morethan the RDA of vitamins, Mayne contends. In fact, there is increasingevidence that excessive intake of certain micronutrients is deleterious.

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

But Mayne and Stampfer both agree that more randomized clinicaltrials are needed to determine the health effects of vitaminsupplements—and that such supplements are critical for certain people.Many African-Americans and people living in sun-deprived areas arevitamin D–deficient and could benefit from supplements, Mayne explains.Pregnant women, and even women who might want to get pregnant, shouldbe taking folic acid supplements to help prevent serious birth defectsin their babies. People over 50 years of age can benefit from B12supplementation because absorption of this vitamin in the digestivetract becomes less efficient with age, says Roberta Anding, spokeswomanfor the American Dietetic Association. Finally, HIV-positive patientsshould take multivitamins to boost immunity and slow the rate ofdisease progression, says Wafaie Fawzi, professor of nutrition andepidemiology at the Harvard School of Public Health.

Ironically, "the people who are most likely to take vitaminsupplements are the people who least need them," Mayne says. Theaffluent and health conscious are popping supplements faster thananyone. It may not be doing any good, and it could be harming them, shesays. Anding concurs: "If you eat well, you probably don't need amultivitamin."
On the other hand, as Stampfer, who takes vitamin supplementhimself, notes: "If I'm wrong, then I've wasted a few dollars. If I'mright, I've lowered my risk for some diseases I don't want to have."



from here
http://www.sciam.com/article.cfm?chanID=sa029&articleID=96D80253-E7F2-99DF-326CCCAF57732EFE&pageNumber=1&catID=9

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发表于 2007-5-30 11:58:27 |显示全部楼层
这两天还在为选修课写维生素的论文~~烦~~
请烤鸭回来的各位板油将回忆写进  每期考试回忆贴 谢谢~~~

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板凳~~

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Golden Apple 寄托兑换店纪念章 寄托16周年纪念勋章

发表于 2009-4-6 22:55:58 |显示全部楼层
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