In the studies, patients were randomly assigned to receive folic acid plus vitamins B12 and B6, folic acid plus B12, or B6 alone, or a placebo. These trials ran from 1998 to 2005, and were followed through the end of 2007.
The researchers found that patients who received folic acid had a 21 percent increased risk for developing cancer. In addition, of the 341 patients who received folic acid and developed cancer, 136 died -- a 38 percent increased risk compared with patients who did not take folic acid and developed cancer.
The most common cancers associated with folic acid were colorectal, lung, prostate and blood cancer, the researchers noted.
In all, 16.1 percent of the patients who were given folic acid plus vitamin B12 died from any cause, compared with 13.8 percent of patients who received neither folic acid nor vitamin B12, the researchers said.
Bettina F. Drake, an assistant professor of surgery at the Alvin J. Siteman Cancer Center of the Washington University School of Medicine in St. Louis and co-author of an accompanying journal editorial, said that "while the results by Ebbing and colleagues provide some short-term data that is important in helping us understand the complexities in the association between folic acid and cancer risk, this report does not nullify the vast potential long-term benefits that folic acid fortification may have on population health."
Drake noted that the dose of folic acid given to patients in the Norwegian studies was significantly higher than what most people in the United States get. "U.S. fortification appears to have left the population well within safe limits," she said.
The true effect of folic acid on cancer may take many years of follow-up to determine, Drake said.
Cancer prevention efforts do not start or end with folic acid, Drake added. "Cessation from cigarette smoking for all who currently smoke and prevention of smoking in our youth and
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