Taking folic acid supplements doesn't appear to prevent colon polyps from coming back, new research shows, although it may be helpful for people who have low levels of the B vitamin in their blood.

These polyps, or adenomas, can develop into cancer if they are not detected and removed. While there's evidence that folate, the natural form of this nutrient, might help protect people from developing colon cancer, studies looking at whether folic acid supplements can ward off adenoma recurrence have had mixed results.

In fact, according to Dr. Kana Wu of the Harvard School of Public Health and colleagues, one study actually found that people who took folic acid supplements were more likely to have recurrent adenomas than people given placebo.

To investigate further, Wu and colleagues assigned nearly 700 men and women participating in the Health Professionals Follow-Up Study and the Nurses' Health Study, two large ongoing studies, to take 1 milligram of folic acid daily or a placebo. All of them had previously been diagnosed with colon polyps.

During follow-up, which lasted for up to six-and-a-half years, 72 people in the placebo group developed recurrent polyps, while 62 in the folic acid group did. This wasn't a statistically significant difference.

However, for people with low concentrations of folate in their blood at the study's outset, taking folic acid reduced recurrent adenoma risk by about 40 percent. The protective effect was particularly strong among people who consumed more alcohol; alcohol is known to deplete a person's folate levels.

This suggests, the researchers conclude, that folic acid supplementation may be beneficial among people with low vitamin B levels who drink a lot of alcohol.

Right now, Wu noted in an email to Reuters Health, the Institute of Medicine says adults should consume no more than 1 milligram of folate daily.

While folic acid supplements are recommended for pregnant women, as well as people with folate deficiency and those taking drugs that interfere with folate metabolism, Wu added, more research is needed to establish what effect taking additional high dose folic acid supplements would have on healthy adults with regard to preventing certain diseases or whether it may even be harmful.

SOURCE: American Journal of Clinical Nutrition, December 2009.