Fewer gallstones arise in active women.

Gallbladder attacks requiring surgery occur less often in women who exercise regularly than in inactive women, a new study shows. A job that keeps a woman on her feet helps, too.

Researchers studying the lifestyles of 60,290 nurses assessed the benefit of exercise by dividing the women into five roughly equal groups according to the extent of their typical exercise programs. The scientists calculated activity based on questionnaire responses detailing how many hours a week a woman did aerobic exercises, ran, swam, hiked, or participated in other sports that required at least moderate exertion.

Over roughly 10 years, those in the most active group, who exercised moderately for at least 2 to 3 hours a week, were only 69 percent as likely to undergo gallbladder removal surgery as the least active women were, scientists report in the Sept. 9 NEW ENGLAND JOURNAL OF MEDICINE. After accounting for differences in body weight, the exercise appeared to cut the risk to 79 percent, says study coauthor Michael F. Leitzmann, an epidemiologist at Harvard School of Public Health and Brigham and Women's Hospital in Boston.

Approaching the lifestyle question from another angle, Leitzmann and his colleagues asked women how many hours they spent each week watching television, sitting at work, and driving a car as part of a daily commute.

The researchers found that watching a lot of TV coincided with a one-third-greater incidence of gallbladder surgery. The women who delegate more than 40 hours a week to sitting at work and driving to it reported nearly 1 1/2 times the number of these gallbladder surgeries as the most active did.

The researchers "went to great lengths to examine the effects of confounding variables, such as age, obesity, and recent change in weight, and the results were the same despite adjustments for these factors," Kenneth J. Vega and David E. Johnston of the University of New Mexico Health Sciences Center in Albuquerque note in the same journal issue.

Leitzmann and his colleagues last year reported a similarly elevated risk of gallstones in sedentary men. Despite these and other gallbladder studies, the biological effect of exercise remains obscure. Exercise might limit stone formation by cutting blood concentrations of LDL cholesterol, the so-called bad cholesterol, Leitzmann says.

High triglyceride concentrations in blood result in the liver adding cholesterol to bile--a digestive juice stored in the gallbladder. There, the saturated bile can form stones of hardened cholesterol, sometimes blocking bile's exit and causing pain. Gallstones necessitate nearly all gallbladder removal surgery.