Cancer protection from fruits and veggies.

Two nutrients in fresh fruits and vegetables may help prevent a precancerous colon condition, according to a new report. A second study adds to evidence that diets rich in such foods help guard against colorectal cancer, a disease that will kill 57,000 Americans this year.

The first study supports previous research suggesting that colon cancers arise when there is a reduction in a biochemical process called methylation -- the addition of methyl side groups to a cell's DNA. Other studies suggest that insufficient methylation activates cancer-causing genes. To accomplish methylation, cells need plenty of folate, a substance abundant in fresh fruits and leafy vegetables. The essential amino acid methionine, a constituent of high-protein foods such as fish, chicken, and dairy products, is also needed during methylation.

Epidemiologist Edward Giovannucci of the Harvard Medical School in Boston and his colleagues report that diets low in folate and methionine may elevate the risk of developing polyps in the colon and rectum.

The Boston researchers sent questionnaires to women participating in the Nurses' Health Study and men enrolled in the Health Professionals Study. The team asked detailed questions about diet and the use of vitamin supplements. They then homed in on men and women who had undergone colonoscopy or sigmoidoscopy, procedures that allow physicians to look at the lining of the rectum and intestine. As it turned out, 564 of the 15,984 women and 331 of the 9,940 men had colon or rectal polyps.

A statistical analysis revealed that study participants with diets rich in folate had the lowest incidence of such polyps. That association held true even when the epidemiologists adjusted for factors that increase the risk of developing colorectal polyps. People who took folate supplements enjoyed even greater protection than those who ate a folate-abundant diet, Giovannucci says.

The researchers also discovered that people who consumed at least two alcoholic drinks per day were 85 percent more likely than nondrinkers to develop colorectal polyps. Alcohol blocks DNA methylation; thus it may be even more important for people who imbibe alcohol to eat plenty of fruits and vegetables, Giovannucci adds.

In the second report, Robert S. Sandler of the University of North Carolina at Chapel Hill and his colleagues confirm earlier studies suggesting that diets rich in fruits and vegetables protect against precancerous colorectal polyps. Although Sandler and his co-workers didn't study folate and methionine specifically, their findings are consistent with those of the Harvard study. Both studies appear in the June 2 JOURNAL OF THE NATIONAL CANCER INSTITUTE.

Despite the increasing list of health benefits ascribed to vitamins and certain nutrients, many researchers advise against taking supplements containing these compounds (SN: 5/22/93, p.327). Public health expert Gladys Block of the University of California, Berkeley, argues that it is time to reconsider that cautious approach.

"There can be no disagreement that people should eat a balanced diet rich in fruits, vegetables, and whole grains," she writes in an editorial in the same issue of the journal. "But people are not eating enough of these foods and are unlikely to do so in the foreseeable future," she notes.

"Our data suggest that there may be a benefit to multivitamin supplements," Giovannucci agrees, noting that most multivitamin pills contain folate. Still, neither of the studies rules out the notion that fresh fruits and vegetables contain some as-yet- unheralded substance that protects against colon cancer. "Our primary recommendation is to eat plenty of fruits and vegetables," he adds.

COPYRIGHT Science Service Inc. 1993