一项研究指出，大鼠母亲在怀孕期间服用了叶酸补充剂，会增加雌性小鼠患乳癌的几率，与其他大鼠相比高达两倍。但是作者强调需要更多的研究来确定是否补充叶酸来防止脊柱裂会导致人类癌症。
　　它们也有更多的肿瘤和发展加快了速度，主导了这项研究的青年博士，圣迈克尔多伦多医院胃肠病学家金说。
　　金正日强调，需要进行更多的研究来以确定是否这项发现也适用于人类。虽然老鼠和人类乳腺癌有相似之处，但是大鼠和人如何代谢叶酸是有差异的。“我们不希望怀孕的妇女恐慌，”他说。
　　过去十年，北美胎儿的叶酸数量大幅增加。在怀孕前和怀孕时女性通常采取叶酸补充剂预防神经管缺陷，如出生后脊柱裂。 自1998年以来，加拿大和美国**已要求食品制造商添加叶酸白面粉，面条和玉米面，以确保妇女获得足够的维生素B。此外，高达40%的北美人采取叶酸补充剂，但是健康性尚未得到证实。
　　饮食中富含天然叶酸，主要存在于谷类和深色的叶类蔬菜中，可能有助于预防癌症。但是金正日发表在二月《癌症研究》的杂志中的研究，增加了越来越多的证据表明，通过摄入高叶酸补充剂可促进某些癌症。
　　在金正日的动物实验中，一半的大鼠给予叶酸补充剂，哺乳期三个星期前和整个交配怀孕期。断奶后，有一半的雌性小鼠得到了数量相同叶酸补充。
　　无论是老鼠的母亲获得了叶酸补充剂还是那些吃了叶酸补充饮食的小鼠与对照组相比乳腺肿瘤的发病率增加了一倍。他们也有更多的肿瘤和快速增长的肿瘤。
　　叶酸有助于使DNA的**。金正日说，叶酸补充剂，减少出现DNA甲基化-如何基因的开启和关闭-这可能起着促进肿瘤的作用。
　　以往的研究表明，怀孕前采取叶酸补充剂可以增加或减少后代某些儿科癌症。但是一些小研究观测，叶酸降低了一些人的神经母细胞瘤，白血病和一些脑肿瘤发病率，但其他人表现出了增加脑部肿瘤几率。金正日去年提出的研究显示孕妇叶酸补充剂降低了后代结肠癌的大约65%的发病率。
　　“这意味着叶酸补充剂影响可能具有器官特异性，“金说。 “它可能会降低某些癌症，但会促进某些人引发癌症。”

爱爱医推荐原文阅读：　　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.