New York, Sep 9 (IANS): Some diabetes drugs can substantially increase the amount of fat inside our bones and thus the risk of bone fractures, warns a new study.

The study also showed that exercise can decrease the volume of bone fat caused by high doses of the diabetes drug rosiglitazone, which is sold under the brand name Avandia.

"We think doctors and patients need to better understand the relationship between diabetes, certain drugs, and the often dramatic effect on bone health," said study first author Maya Styner, assistant professor at University of North Carolina School of Medicine in the US.

Essentially, rosiglitazone takes glucose out of blood to lower blood sugar and treat diabetes.

But that glucose is then packaged into lipid droplets - fat.

Other researchers showed that some of that fat is stored in tissue, such as belly fat.

The latest research conducted in mice showed that the drug also causes fat to be stored inside bone.

"We were surprised by the massive amount of bone fat caused by rosiglitazone," Styner said.

To see the effect of exercise, the study team added a running wheel to mouse cages. Mice are natural runners and at night, they would run several miles on the wheel.

Even on a high dose of a power drug, such as rosiglitazone, the mice that exercised showed a significant decrease in bone fat.

Styner said exercise might trigger marrow stem cells to create more bone cells instead of fat cells. Or perhaps exercise causes the body to access bone fat as fuel.

"It could be that bone fat is just another depot, a good energy store that allows bone cells to do what they need to do so bones become stronger," Styner said.

The study was published in the journal Endocrinology.