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Short-term use of these supplements is unlikely to increase or decrease overall cancer risk and has little effect on the likelihood of developing specific cancers, such as colon, prostate, lung and breast cancers, U.K. researchers found.
The research was published online Jan. 24 in The Lancet.
"The study provides reassurance about the safety of folic acid intake, either from supplements or through fortification, when taken for up to five years," study author Robert Clarke, from the University of Oxford, said in a journal news release.
"The nationwide fortification of foods involves much lower doses of folic acid than studied in these trials, which is reassuring not only for the U.S.A., who have been enriching flour with folic acid to prevent neural tube birth defects [such as spina bifida] since 1998, but also for over 50 other countries where fortification is mandatory [such as] Australia, South Africa, Chile, Argentina and Brazil," Clarke said.
The researchers analyzed all large randomized trials of folic acid supplements with or without other B vitamins up to the end of 2010. Their analysis involved roughly 50,000 people.
Those who took folic acid every day for up to five years were not significantly more likely to develop cancer than other people who took placebo pills, the study revealed. The investigators found that 7.7 percent of those who took folic acid developed cancer, while 7.3 percent in the placebo group were also diagnosed.
Even those who took the highest average daily intake of folic acid did not increase their risk for cancer, the researchers noted. Nor did they find evidence that taking folic acid for longer periods of time increased the risk for cancer.
"Both the hopes for rapid cancer prevention and the fears about rapidly increased cancer risk from folic acid supplementation were not confirmed by this meta-analysis," Clarke said. "It remains to be seen whether any beneficial or harmful effects on cancer incidence will eventually emerge with even longer treatment or follow-up."
In an accompanying commentary, Cornelia Ulrich, director of the National Center for Tumor Diseases and German Cancer Research Center, and Joshua Miller, from Rutgers University, said it's important to note that folate may protect against the development of cancer, but also cause existing cancer cells to grow.
This is particularly important, they added, because 1 percent to 4 percent of Americans exceed the tolerable daily limit for total folic acid intake (1 milligram per day) by consuming both fortified foods and supplements.
-- Mary Elizabeth Dallas
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