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(Ivanhoe Newswire) -- Patients with heart disease in Norway, a country where foods are not fortified with folic acid, had an increased risk of cancer and death from any cause if they received treatment with folic acid and vitamin B12.
Most epidemiological studies have found inverse associations between intake of folate, a B vitamin, and risk of colorectal cancer. Similar associations have been inconsistent or absent for other cancers, however.
Marta Ebbing, M.D., of Haukeland University Hospital, Bergen, Norway, and colleagues analyzed the results of two Norwegian trials among patients with ischemic heart disease, where there was a statistically insignificant increase in cancer incidence in the groups assigned to folic acid treatment. The researchers examined whether folic acid treatment was associated with cancer outcomes and all-cause mortality after extended follow-up. The authors were quoted as saying, "Because there is no folic acid fortification of foods in Norway, this study population was well suited for such an investigation."
"Experimental evidence suggests that folate deficiency may promote initial stages of carcinogenesis, whereas high doses of folic acid may enhance growth of cancer cells, the authors wrote. Since 1998, many countries, including the United States, have implemented mandatory folic acid fortification of flour and grain products to reduce the risk of neural-tube birth defects. Recently, concerns have emerged about the safety of folic acid, in particular with respect to cancer risk."
The two clinical trials included 6,837 patients with ischemic heart disease who were treated with B vitamins or placebo between 1998 and 2005, and were followed up through the end of 2007.
The researchers found that after a median 39 months of treatment and an additional 38 months of post-trial follow-up, 288 participants who did not receive folic acid plus vitamin B12 versus 341 participants who received such treatment were diagnosed with cancer, representing a 21 percent increased risk.
A total of 100 patients who did not receive folic acid plus vitamin B12 versus 136 who received such treatment died from cancer, a 38 percent increased risk. A total of 16.1 percent of patients who received folic acid plus vitamin B12 vs. 13.8 percent who did not receive such treatment died from any cause.
"Results were mainly driven by increased lung cancer incidence in participants who received folic acid plus vitamin B12. Vitamin B6 treatment was not associated with any significant effects," the authors wrote. "Our results need confirmation in other populations and underline the call for safety monitoring following the widespread consumption of folic acid from dietary supplements and fortified foods."
SOURCE: Journal of the American Medical Association (JAMA), November 18, 2009
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