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【科普】心脏研究表明奶茶无益
Heart study pours cold water on adding milk to tea
Last Updated: Tuesday, January 9, 2007 | 12:55 PM ET
CBC News
Adding milk to tea nullifies the heart-healthy benefits of the hot beverage, a new study suggests.
In Tuesday's edition of European Heart Journal, researchers said tests on volunteers showed that black tea significantly improves the ability of arteries to relax and expand, but those effects are cancelled out when milk is added.
Adding milk to tea seems to reduce the effects of heart-healthy compounds in the drink.
(Canadian Press) "We found that, whereas drinking tea significantly increased the ability of the artery to relax and expand to accommodate increased blood flow compared with drinking water, the addition of milk completely prevents the biological effect," said the study's first author, Mario Lorenz, a molecular biologist at Charite Hospital at the University of Berlin.
Tests on the aortas of rats and endothelial cells lining the heart pointed to the same result, Lorenz and his colleagues found.
Tea is the second-most widely consumed beverage worldwide after water, according to the researchers.
The findings may help explain why the risk of heart disease and stroke isn't significantly reduced in countries such as Britain where tea with milk is popular.
Casein proteins in milk reduce the amount of catechin compounds in tea that protect against heart disease, perhaps by mixing with the catechins, said study co-author Dr. Verena Stangl, a professor of cardiology at the university.
In the study, 16 healthy women aged 50 or more drank either half a litre of freshly brewed black Darjeeling tea, black tea with 10 per cent skimmed milk or boiled water as a control three separate times.
Researchers measured the endothelial function of the brachial artery in forearm using high-resolution ultrasound before and after the drinks were consumed. Measurements were taken every 15 seconds for up to two minutes each.
Tests on rats also showed that rodents given black tea produced more nitric oxide, which promotes dilation of blood vessels. The effect did not happen when milk was added to the tea.
Previous research has suggested that tea may also have protective benefits against cancer.
"Since milk appears to modify the biological activities of tea ingredients, it is likely that the anti-tumor effects of tea could be affected as well," said Stangl.
The study did not look at the effects of green tea, which is widely consumed in East Asia without milk, or at the effects of adding soy milk. 本人认领该文编译，今上交. http://www.dxy.cn/bbs/post/view?bid=116&id=8011003&sty=1&tpg=2&age=0 新浪投稿
研究表明奶茶对心脏无益
欧洲心脏杂志周二报道，研究者发现黑茶可明显改善受试者动脉血管的舒展弹性，而一旦加上牛奶则无此效果，得出奶茶对心脏无益的结论。
柏林大学Charite医院的分子生物学家Mario Lorenz是本文第一作者，他说：“我们发现，与普通饮用水相比，茶水能显著提高动脉舒展弹性，能很好适应血流增加变化，然而加入牛奶的话这种生物学效应会被彻底阻断”。因此，奶茶可能降低对心脏有益的化合物的作用。
据研究者称除饮用水外茶水是全世界第二大饮料。该调研结果可解释为什么在奶茶消费大国英国，心脏疾病和中风的发病风险一直无明显下降趋势。
本项研究包括16例健康女性，年龄均在50岁或以上。受试者每人喝半升加入十分之一量脱脂牛奶的大吉岭黑茶或直接喝白开水，共进行了3组实验。采用高频超声仪器对受试者上臂肱动脉血管内皮功能进行监测，每次测试间隔15秒，最长间隔2分钟。
Lorenz和他同事在大鼠动脉和心脏内皮细胞的实验中也证实了这一点。大鼠实验表明给予啮齿类黑茶能产生较多的一氧化氮，一氧化氮则能扩张血管，再给予牛奶后这种效应也就没有了。
牛奶酪蛋白可能与能茶水中儿茶酚结合从而降低茶水中儿茶素化合物含量，而后者可预防心脏疾病，柏林大学Charite医院研究合著者心脏学专家Verena Stangl博士讲道。
以往研究还表明茶还可预防癌症发生。由于牛奶改变了茶的生物作用，所以奶茶的抗癌作用也就受影响了。
该研究不能看出绿茶的功效。在东亚地区大多喝绿茶，并且不和牛奶放一起喝的，即使混合也是豆奶之类。 [标签:content1][标签:content2]
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作者:admin@医学,生命科学 2011-03-30 15:20
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