TUESDAY, June 5, 2007 (HealthDay News) -- Not only won't folic acid prevent colorectal cancer in people with a history of colon polyps, new research suggests that the vitamin supplement may actually help those cancers grow.
Three years after taking one milligram of folic acid daily, those with a history of polyps had a 32 percent higher risk of having an advanced adenoma (polyp) compared to the group taking a placebo pill daily, researchers are reporting. An advanced adenoma indicates that a polyp has undergone pre-cancerous changes in its cells that may later develop into colon cancer.
"We found that folic acid supplements were not useful for preventing adenomas and that this population tended to do worse on folic acid, which was a surprise," said the study's lead author, Bernard Cole, an associate professor of community and family medicine at Dartmouth Medical School.
The findings are published in the June 6 issue of the Journal of the American Medical Association.
Each year, about 145,000 Americans are diagnosed with colorectal cancer, according to the U.S. Centers for Disease Control and Prevention, and about 56,000 die annually from the disease.
Previous observational studies had indicated that folic acid might be effective at decreasing colon cancer, and the polyps that eventually develop into the disease, because people with low levels of folate -- the natural form of folic acid, a B vitamin -- were more likely to develop colon cancer and polyps, Cole explained.
To better assess folic acid's cancer-prevention ability, Cole and his colleagues designed a double-blind, placebo-controlled, randomized trial that included slightly more than 1,000 adults who had a history of recent adenomas. Their adenomas had been removed during a colonoscopy prior to the start of the study.
Half the participants were randomly selected to take 1 milligram of folic acid daily for the duration of the study, while the rest were given a placebo. The daily recommended amount of folic acid is 400 micrograms, less than half that given to the study participants, according to the National Institutes of Health. Pregnant women are advised to get 600 micrograms daily, because folic acid has been shown to reduce birth defects.
The study volunteers underwent two more colonoscopies, one after three years and then another after an additional three to five years.
After the first round of colonoscopies, the researchers found that the incidence of at least one adenoma was 44.1 percent for those on folic acid and 42.4 percent for those taking the placebo. Of more concern was that those taking folic acid had a 32 percent higher risk of having an advanced adenoma than the placebo group.
Only 60 percent of the study participants underwent the second follow-up colonoscopy. But in those who did, 41.9 percent of those taking folic acid had at least one adenoma, compared to 37.2 percent of those taking a placebo. The risk of an advanced adenoma was 67 percent higher for the folic acid group.
The researchers found no significant effect on the results when they factored in sex, age, smoking history, aspirin use, alcohol use, body mass index, and average folate levels.
Cole said that while the results were surprising, other studies may offer an explanation. "Some of these studies have shown that folate seems to have a dual effect on cancer development. High levels of folate tend to prevent cancer if there's no cancer in the system. On the other hand, other studies suggest that folate may feed undetectable microscopic lesions," he said.
Cole emphasized that this study's findings only apply to people with a history of polyps and not to the population in general.
Cornelia Ulrich, an associate member of the cancer prevention program at the Fred Hutchinson Cancer Research Center in Seattle, said, "This was an important trial that showed clearly there's no benefit from taking folic acid for patients with prior polyps, and possibly, there could be some harm."
Ulrich, who co-wrote an editorial in the same issue of the journal, said she's concerned that people who take supplements, eat fortified foods and eat or drink so-called health drinks or snack bars, may end up consuming as much folic acid as was used in this study.
"People who have had a polyp should carefully review how much additional folic acid they get from health bars and drinks," she said.
And, anyone getting treatment for colon and other cancer should discuss any use of supplements -- folic acid or others -- with their doctor, because they could interfere with their treatment.
Both Cole and Ulrich said the most important step anyone can take for colon cancer prevention is to follow whatever colonoscopy screening schedule their doctor recommends.
More information
To learn more about preventing colorectal cancer, visit the American Cancer Society.
