Daily doses of vitamins B-6, B-12 and folate (B-9) don’t raise or lower a woman’s risk of getting cancer, researchers report in the Nov. 5 Journal of the American Medical Association.
The large trial may put to rest suggestions raised by smaller studies that these vitamins might deter certain cancers or, as one study suggested, increase them.
All three vitamins play key roles in DNA synthesis. Ten years ago, the United States began to fortify many foods with folic acid, the synthetic version of folate. The specific aim was to prevent neural tube defects in newborn babies resulting from a folate shortage during pregnancy.
Meanwhile, several studies have hinted that supplemental folate and B vitamins inhibited colorectal and breast cancer. But a study published in 2007 found no benefit and even hinted that folate supplements might increase the risk of colon cancer.
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The new findings come from a trial conducted from 1998 to 2005 in which researchers randomly assigned half of 5,442 women to get supplements of all three vitamins, while the others received placebos.
The participants were professional women age 42 years or older. Their average age was 63 and the women were, on average, moderately overweight.
During the seven-year trial, 187 women getting the vitamins and 192 taking the placebo developed cancer, an insignificant difference. Within those groups, 70 of those getting the vitamins and 84 of those on the fake pills developed breast cancer, a difference also considered insignificant.
“We definitely provide evidence that there is no beneficial or harmful effect on their cancer risk,” says study coauthor Shumin Zhang, an epidemiologist at Harvard Medical School and Brigham and Women’s Hospital in Boston.
When Zhang and her colleagues limited the analysis to women age 65 or over, they found that those getting the vitamins were 25 percent less likely to develop cancer. The concept is biologically plausible, the authors note, since older people have greater-than-average requirements for these essential vitamins.
But this apparent benefit from vitamins for the women over 65 barely passed muster statistically. “It could be due to chance,” Zhang says. “Someone needs to follow up with further study.”