一項(xiàng)研究指出，大鼠母親在懷孕期間服用了葉酸補(bǔ)充劑，會(huì)增加雌性小鼠患乳癌的幾率，與其他大鼠相比高達(dá)兩倍。但是作者強(qiáng)調(diào)需要更多的研究來確定是否補(bǔ)充葉酸來防止脊柱裂會(huì)導(dǎo)致人類癌癥。
　　它們也有更多的腫瘤和發(fā)展加快了速度，主導(dǎo)了這項(xiàng)研究的青年博士，圣邁克爾多倫多醫(yī)院胃腸病學(xué)家金說。
　　金正日強(qiáng)調(diào)，需要進(jìn)行更多的研究來以確定是否這項(xiàng)發(fā)現(xiàn)也適用于人類。雖然老鼠和人類乳腺癌有相似之處，但是大鼠和人如何代謝葉酸是有差異的。“我們不希望懷孕的婦女恐慌，”他說。
　　過去十年，北美胎兒的葉酸數(shù)量大幅增加。在懷孕前和懷孕時(shí)女性通常采取葉酸補(bǔ)充劑預(yù)防神經(jīng)管缺陷，如出生后脊柱裂。 自1998年以來，加拿大和美國**已要求食品制造商添加葉酸白面粉，面條和玉米面，以確保婦女獲得足夠的維生素B。此外，高達(dá)40%的北美人采取葉酸補(bǔ)充劑，但是健康性尚未得到證實(shí)。
　　飲食中富含天然葉酸，主要存在于谷類和深色的葉類蔬菜中，可能有助于預(yù)防癌癥。但是金正日發(fā)表在二月《癌癥研究》的雜志中的研究，增加了越來越多的證據(jù)表明，通過攝入高葉酸補(bǔ)充劑可促進(jìn)某些癌癥。
　　在金正日的動(dòng)物實(shí)驗(yàn)中，一半的大鼠給予葉酸補(bǔ)充劑，哺乳期三個(gè)星期前和整個(gè)交配懷孕期。斷奶后，有一半的雌性小鼠得到了數(shù)量相同葉酸補(bǔ)充。
　　無論是老鼠的母親獲得了葉酸補(bǔ)充劑還是那些吃了葉酸補(bǔ)充飲食的小鼠與對照組相比乳腺腫瘤的發(fā)病率增加了一倍。他們也有更多的腫瘤和快速增長的腫瘤。
　　葉酸有助于使DNA的**。金正日說，葉酸補(bǔ)充劑，減少出現(xiàn)DNA甲基化-如何基因的開啟和關(guān)閉-這可能起著促進(jìn)腫瘤的作用。
　　以往的研究表明，懷孕前采取葉酸補(bǔ)充劑可以增加或減少后代某些兒科癌癥。但是一些小研究觀測，葉酸降低了一些人的神經(jīng)母細(xì)胞瘤，白血病和一些腦腫瘤發(fā)病率，但其他人表現(xiàn)出了增加腦部腫瘤幾率。金正日去年提出的研究顯示孕婦葉酸補(bǔ)充劑降低了后代結(jié)腸癌的大約65%的發(fā)病率。
　　“這意味著葉酸補(bǔ)充劑影響可能具有器官特異性，“金說。 “它可能會(huì)降低某些癌癥，但會(huì)促進(jìn)某些人引發(fā)癌癥。”

愛愛醫(yī)推薦原文閱讀：　　Authors stress more research needs to be done to determine whether supplement that prevents spina bifida causes cancer in humans.The daughters of rats who took folic acid supplements before conception, during pregnancy and while breast-feeding have breast cancer rates twice as high as other rats, according to a new study.
　　They also had more tumours and developed them at a faster rate, according to the study led by Dr. Young-in Kim, a gastroenterologist at St. Michael's Hospital in Toronto.
　　Kim stressed more research needs to be done to determine whether the findings also apply to humans. While there are similarities in breast cancer in rats and humans, there are differences in how rats and human metabolize folic acid. "We don't want pregnant women to panic," he said.
　　The amount of folic acid to which fetuses are exposed has increased dramatically in North America in the past decade. Women are routinely advised to take folic acid supplements before becoming pregnant and while pregnant to prevent neural tube birth defects such as spina bifida. Since 1998, the Canadian and U.S. governments have required food manufacturers to add folic acid to white flour, enriched pasta and cornmeal products as a way of ensuring women receive enough of the B vitamin. In addition, up to 40 per cent of North Americans take folic acid supplements for possible but as yet unproven health benefits.
　　A diet rich in natural folate, found in grains and dark, leafy vegetables, may help prevent cancer. But Kim's study, published in the February issue of the journal Cancer Research, adds to a growing body of evidence that high folate intake through supplements may promote some cancers-and prevent others.
　　In Kim's animal study, half the rats were given folic acid supplements -- equivalent to what pregnant women in North America take in addition to the mandatory fortification in some foods - three weeks before mating and throughout the pregnancy and lactation. After weaning, half the female pups received the same amount of folic acid supplement as the pregnant rats.
　　Both the rats whose mothers took folic acid supplements and those who ate a folic acid supplemented diet had a twofold increase in rates of mammary tumours than the control groups. They also had more tumors and faster-growing tumors.
　　The folic acid supplements given to pregnant rats seemed to have a more profound tumour-producing effect than the supplements given to infant rats, suggesting that folic acid has more impact on a developing fetus than babies, Kim said.
　　Folate helps to make DNA and help it replicate. Kim said the folic acid supplements appear to decrease DNA methylation - how genes are turned on and off - and this likely plays a role in promoting tumors.
　　Previous studies have shown that folic acid supplements taken before conception can either increase or decrease certain pediatric cancers in offspring. Some of these small, observational studies have linked folic acid to a decrease in neuroblastomas, leukemia and some brain tumours, but others have shown an increase in brain tumours. Kim presented research last year showing maternal folic acid supplements decreased colon cancer in offspring by about 65 per cent.