A study that set out to test folate for prevention of early-stage colon cancer instead found a higher incidence of colorectal adenomas in the test group. This multi-institutional research, performed by the Polyp Prevention Study Group, appeared in the June 6 Journal of the American Medical Association.

The cohort included 987 people who had a history of colorectal adenomas, precursor lesions for cancer. Half of these people received 1 mg/day of folic acid and the other half received a placebo. The average person gets about 0.2 - 0.4 mg of daily folate in their diet. Participants were monitored with colonoscopies after 3 and 5 years.

With an average follow-up of 3 years, colorectal adenomas occurred in 42.4 percent of participants who received the placebo and in 44.1 percent of those who received folic acid. At the 5-year follow-up, participants in the folic acid group also had higher rates of advanced lesions and greater numbers of lesions than the control group.

An accompanying editorial speculates that the most likely explanation for this increase in advanced lesions (known precursors to colorectal cancer) is that they are promoted by increased folate.

The editorial also notes that a history of colorectal adenomas was a prerequisite for inclusion in the study, and the endpoint was whether additional adenomas formed, not whether cancer was prevented in this high-risk group. "The question of efficacy of folate in cancer prevention is not resolved…Animal experiments showing chemopreventive effects of folate, as well as the strong observational epidemiological evidence, speak to [its] potential…if taken early," the editorialists wrote.