THURSDAY, Sept. 17 (HealthDay News) -- Green tea may weaken bones, suggests a U.S. study on mice.

Obese and lean mice had different amounts of green tea extract -- 0 percent, 1 percent or 2 percent -- added to their diets. Previous studies had found that consumption of the equivalent of 1 percent of the extract decreased the risk of cardiovascular disease in Japanese adults and protected obese mice against fatty liver disease.

After mice in the new study had consumed the experimental diet for six weeks, their bones were analyzed for size, mineral content and architecture. Mice that ate a diet that included green tea extract weighed less than those that did not have the extract added to their food. The difference was more pronounced among obese mice, the researchers noted.

The mineral density of the large bone in the leg, the femur, was not affected by body weight, the study found. However, consumption of green tea extract appeared to reduce femur length, volume, mineral content and cortical thickness. A similar effect was noted in lumbar vertebrae, according to the study published in the October issue of the Journal of Nutrition.

The findings suggest that consumption of green tea extract can cause harmful changes in bone microarchitecture and reduce bone size in growing mice. It's not clear whether similar effects occur in humans, according to the researchers, from Oregon State University and the University of Connecticut.

More information

The U.S. National Center for Complementary and Alternative Medicine has more about green tea.