No evidence of cancer risk from folate supplementsBMJ 2013; 346 doi: http://dx.doi.org/10.1136/bmj.f546 (Published 30 January 2013) Cite this as: BMJ 2013;346:f546
Concerns about links between folate supplements and some types of cancer led researchers to reanalyse the individual datasets of 13 placebo controlled trials. The pooled results were reassuring. Participants taking folate supplements were no more likely than controls to develop new cancers during an average follow-up of five years (1904 cancers in the folic acid groups v 1809 cancers in the placebo groups; relative risk 1.06, 95% CI 0.99 to 1.13). They took between 0.5 mg and 5 mg a day, alone or in combination with B vitamins. The authors found no excess of any cancer type associated with folate supplements, and no link between cancer risk and duration of supplementation⇑.
The authors hope their new analyses will help inform a longstanding debate about fortifying flour with extra folate to help prevent neural tube defects. Flour is already fortified in 50 countries including the US, Canada, and Australia. European governments have been more cautious, partly because a small transient spike in colorectal cancers occurred during the roll-out period in the US and Canada. These authors think it unlikely that fortification was responsible. The typical daily doses of folate from fortified flour are an order of magnitude smaller than the doses tested in trials of supplements. Three of the trials in their meta-analysis recruited adults with a previous colorectal adenoma.
Biologically, extra folate could reduce the risk of new cancers while encouraging growth of preclinical ones, says a linked editorial (doi:10.1016/S0140-6736(13)60110-5). This complex relationship with cancer can be hard to see, even in large datasets. We should interpret with caution for now.
Cite this as: BMJ 2013;346:f546