Folate tied to lower colon cancer risk
By Genevra Pittman
NEW YORK (Reuters Health) - People who eat plenty of folate had a lower risk of colon and rectal cancers in a new study that examined the effects of folic acid fortification in the United States.
In addition, the study did not find any extra cancer-related danger at very high levels of folate -- as some researchers have worried -- over close to a decade.
The benefit and possible harm of folate is "definitely still an open question," said study author Todd Gibson, from the National Cancer Institute in Rockville, Maryland. But, he said, "there seems to be an association between people who report higher folate with those people who have a lower risk of colorectal cancer."
In the late 1990s, the U.S. and Canadian governments began requiring that folic acid (a synthetic form of folate) be added to grain products in order to prevent some birth defects that had been linked to low folate levels in pregnant women.
While previous studies have generally suggested that a diet rich in folate decreases the risk of colorectal cancer as well, most of those were done before fortification started, Gibson said. To see if the government mandate affected that link, the researchers used data from a diet survey started in 1995 that included more than 500,000 middle-aged and older U.S. adults.
At the start of the study, participants filled out a questionnaire about their normal eating habits and any supplements they took regularly. From that, the researchers were able to calculate how much folate they got on a typical day before and after fortification started.
For the next ten years or so, they tracked cancer registries to see which participants were diagnosed with colorectal cancer. They found a total of about 7,200 cases in their original sample, including about 6,500 that were diagnosed after the start of the fortification program.
People who ate the highest amount of folate each day (at least 900 micrograms post-fortification) were 30 percent less likely to get colorectal cancer than those who got less than 200 micrograms each day, the researchers reported in the American Journal of Clinical Nutrition.
That was after taking into account weight, smoking, physical activity, and certain other aspects of diet. Still, Gibson said that the findings can't prove that increased folate drove the cancer benefits, because "people who report high levels of folate tend to be healthy in other ways," possibly including some the researchers didn't record.
The recommended daily allowance for folate is 400 micrograms for most adults and 600 micrograms for pregnant women. Along with fortified cereals and other grains, vegetables and beans are good sources of folate, a type of B vitamin.
As a result of fortification, the average person's folate intake through foods increased by about 100 micrograms.
Gibson's study did not find any upticks in cancer rates at folate levels far above that recommended daily allowance.
Concern over the possibility that too much folate could raise cancer risk had mostly come from studies in animals, said Dr. Young-In Kim, a nutrition and cancer researcher from the University of Toronto.