The study led by Kenneth Wilund, a faculty member in the I Division of Nutritional Sciences and an Assistant Professor in Kinesiology and Community Health has identified potential mechanisms to explain the reason behind this phenomenon. "For the first time, we have direct evidence that physical activity reduces gallstone formation, adding to the ever-increasing number of reasons that people should get more exercise," said Wilund. He also said that gallstones are formed when bile cholesterol levels become high enough to precipitate, fall out of solution, and solidify. For the study, the researchers fed 50 mice from a gallstone-susceptible strain with a high-fat diet containing cholic acid, helping to increase cholesterol absorption. Later, they were divided into two groups: One group of mice ran on treadmills 45 minutes per day five days a week; the other group did not exercise.
12 weeks later, the researchers took out the animals' gallbladders, pooling the stones from each group and weighing them. It was found that the gallstones in the sedentary group weighed two and a half times more than the stones in the exercised group. "You could see through the gallbladders in the exercise-trained group, whereas the gallbladders in the sedentary group were full of stones," said Wilund.
In order to know more about why this happened, the researchers measured the expression of selected genes in the liver and intestine, involved in cholesterol absorption and may affect gallstone development.
"In the exercised mice, we saw an increase in the expression of two genes (LDLr and SRB1) that help bring cholesterol into the liver to 'clear' it from the circulation. But we also found that a protein called Cyp27 was upregulated about two a half times; this resulted in there being more bile acids to solubilize the increased cholesterol so it didn't turn into gallstones. Taken together, the differences in gene expression between the exercised and sedentary mice in this study show how exercise training could simultaneously improve cholesterol levels while also inhibiting gallstone formation," he said.
It was indicated through earlier observational studies that physically fit people have fewer gallstones and lower cholesterol, however, this link was not confirmed by laboratory studies. Wilund said that these mice are a useful model as humans have a similar set of genes that regulate liver and bile cholesterol metabolism. He also said that human studies would be difficult to perform because of the number of years it takes for people to develop gallstones.
"We certainly found the changes in gene expression in the exercised animals very intriguing. The results add to a body of evidence that supports the importance of physical activity for good health," he said. The study is recently published in the Journal of Applied Physiology.