A recent randomized, placebo-controlled study indicates that folic acid supplementation does not lower the risk of colorectal adenomas, and instead might actually increase risk.

Men and women in the US with a history of colorectal adenomas, but no history of invasive carcinoma, were randomized to receive either 1 mg a day of folic acid (n = 516) or placebo (n = 505). Follow-up included one colonoscopy after 3 years of treatment and a second 3–5 years later. The incidence of colorectal adenomas was not reduced by folic acid during the first or second follow-up periods, or when data from both periods were examined together. Similarly, folic acid did not reduce the incidence of advanced adenomas or multiple adenomas, and in fact there was a trend for incidence to be higher in patients who took folic acid. Furthermore, folic acid did not appear to be beneficial even in subgroups of patients who might be more likely to benefit (for example, those who drank alcohol or who had low baseline folate levels).

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