TUESDAY, Nov. 17 (HealthDay News) -- The use of folic acid and vitamin B₁₂ supplementation is associated with increased cancer incidence and cancer mortality, according to research published in the Nov. 18 issue of the Journal of the American Medical Association.

Marta Ebbing, M.D., of the Haukeland University Hospital in Bergen, Norway, and colleagues analyzed data from 6,837 participants in two trials in Norway, where food is not fortified with folic acid. Participants received folic acid and vitamin B₁₂ with or without vitamin B₆, vitamin B₆ alone, or placebo. Participants were treated for roughly 39 months and followed afterward for another 38 months.

The researchers found that the treatment with folic acid and B₁₂ was associated with significantly increased cancer incidence (hazard ratio, 1.21) and significantly increased cancer mortality (hazard ratio, 1.38). The findings appeared to be largely due to higher lung cancer incidence in treated individuals (hazard ratio, 1.59).

"Experimental findings suggest that excess folic acid may stimulate the growth of established neoplasms (i.e., the so-called acceleration phenomenon). However, it is plausible that folic acid given for a median of 39 months may have influenced growth in cancers that were silent at baseline or during trials," the authors write. "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."

The underlying trials were funded in part by Alpharma Inc., which provided study medication. A co-author is employed by Bevital AS.

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