Folic acid supplements and cancer

Folate has a role in DNA production and repair. Although it is found in fruits and vegetables, foods may be fortified with folic acid. This synthetic form of folate is also available in supplements.

A Norwegian group has carried out a systematic review of 19 studies that assessed the risk of cancer in people taking folic acid supplements. 

Ten trials reported 3515 cancers in 38,233 people. Compared with placebo, the relative risk of cancer was slightly higher with folic acid.

Overall, the raised risk of cancer was not statistically significant. 

Six randomised trials reported 1134 cancer-related deaths. Although the relative risk was increased in people taking folic acid, it was only significant in trials involving a large proportion of smokers.

A limitation of the systematic review was that many trials were not in the general population. Seven trials were in people who had, or were at high risk of heart disease.