过量服用营养保健品或增加个体患癌风险

  很多广告都打出了膳食补充剂（营养保健品）可促进机体健康的理念，但近日在2015年美国癌症研究协会年会(AACR)上，来自科罗拉多大学癌症研究中心的研究人员却表示，直接售给消费者的膳食补充剂，如果每日超过推荐剂量过量服用的话或许会增加个体的患癌风险。
  研究者Byers表示，我们并不确定这些膳食补充剂在分析水平上所发生的事件，但有证据表明，超过需求量过量服用膳食补充剂或可增加个体的患癌风险；通过20年的观察研究分析显示，多吃水果及蔬菜的个体更倾向具有较低的患癌风险，而研究者想知道是否额外的维生素及矿物质是否会降低患癌风险。
  当研究者首次在动物模型中检测膳食补充剂和其患癌风险的关系时，研究结果非常不错，最终当研究者将实验转移到人类研究中时，他们对服用安慰剂及膳食补充剂的数千名个体进行了长达10年的研究，但最终结果并不像他们预测的那样。膳食补充剂实际上对机体健康并无益处，某些个体当其服用维生素时往往会增加其患癌风险。
  一项进行β-角蛋白补充剂的临床试验结果表明，超过推荐剂量服用补充剂会增加20%的个体患肺癌和心脏病的风险；而叶酸，被认为可以降低结肠息肉的补充剂，实际上也会增加患癌风险。但这并不是说人们应当警惕服用维生素和矿物质，如果以正确剂量来服用的话，微量元素对机体是有意的，但其并不能代替正常的营养食物。
  最后Byers表示，正常个体应当通过每天的健康饮食来获得每日所需剂量的维生素和矿物质，而且许多成年人并不需要服用膳食补充剂；最后研究者指出，服用额外的膳食补充剂对机体弊大于利。（转化医学网360zhyx.com）
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While dietary supplements may be advertised to promote health, a forum at the American Association for Cancer Research (AACR) Annual Meeting 2015 by University of Colorado Cancer Center investigator Tim Byers, MD, MPH, describes research showing that over-the-counter supplements may actually increase cancer risk if taken in excess of the recommended daily amount.

"We are not sure why this is happening at the molecular level but evidence shows that people who take more dietary supplements than needed tend to have a higher risk of developing cancer," explains Byers, associate director for cancer prevention and control at the CU Cancer Center.

The line of research started 20 years ago with the observation that people who ate more fruits and vegetables tended to have less cancer. Researchers including Byers wanted to see if taking extra vitamins and minerals would reduce cancer risk even further.

"When we first tested dietary supplements in animal models we found that the results were promising," says Byers. "Eventually we were able to move on to the human populations. We studied thousands of patients for ten years who were taking dietary supplements and placebos."

The results were not what they expected.

"We found that the supplements were actually not beneficial for their health. In fact, some people actually got more cancer while on the vitamins," explains Byers.

One trial exploring the effects of beta-keratin supplements showed that taking more than the recommended dosage increased the risk for developing both lung cancer and heart disease by 20 percent. Folic acid, which was thought to help reduce the number of polyps in a colon, actually increased the number in another trial.

"This is not to say that people need to be afraid of taking vitamins and minerals," says Byers. "If taken at the correct dosage, multivitamins can be good for you. But there is no substitute for good, nutritional food."

Byers says that people can get the daily recommended doses of vitamins and minerals in their diets by eating healthy meal and that many adults who take vitamin supplements may not need them.

"At the end of the day we have discovered that taking extra vitamins and minerals do more harm than good," says Byers.