By Anthony J. Brown, MD

NEW YORK (Reuters Health) - In a study of over 40,000 runners, body mass index (BMI) was positively related to the risk of gallbladder disease, while running speed and distance and cardiorespiratory fitness were inversely tied to the risk.

Prior studies have yielded conflicting results regarding the impact of physical activity on the risk of gallbladder disease, study author Dr. Paul T. Williams, from the Ernest Orlando Lawrence Berkeley National Laboratory in California, points out.

The discrepancies may relate to the fact that most studies to date have not included many subjects engaging in vigorous physical activities, defined as those that require an energy expenditure sixfold or greater than resting levels, according to the report.

In contrast to other studies, the National Runners' Health Study specifically targeted vigorously active men and women. The current analysis of NRHS data included 29,110 male and 11,953 female runners.

During an average follow-up period of about 7.5 years, 166 men and 112 women were diagnosed with gallbladder disease, the report indicates.

As BMI rose, so did the risk of gallbladder disease, particularly once BMI reached 27.5. BMI is the ratio of height to weight that is used to estimate whether an individual is over- or underweight. A BMI between 18.5 and 24.9 is considered a normal weight

However, even within the normal BMI range there was evidence of direct association with risk. For example, compared with the leanest women, those with a BMI above 22.5 were at increased risk.

Cardiorespiratory fitness was inversely related to the risk of gallbladder disease, after adjusting the data to take into account BMI and daily running distance. Men who ran at 4.75 meters per second or faster on a 10 km race were 75 percent less likely to develop gallbladder disease than those who ran at less than 3.25 m/s. Similarly, women who ran 4.0 m/s or faster were 85 percent less likely to develop the disease compared with those ran at less than 2.8 m/s.

A significant inverse association was also seen between usual running distance and gallbladder disease risk. This finding, which was noted in both men and women, was thought to relate to the lean body habitus of longer-distance runners.

A lower level of cardiorespiratory fitness, and other factors associated with a slower 10 km race performance, are "previously undescribed risk factors" for gall bladder disease, Williams concludes. "Prior reports that have interpreted fitness as simply a more objective measure of physical activity may ignore the importance of the metabolic factors that define fitness and improve performance."

SOURCE: American Journal of Gastroenterology, September 2008.

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