In a rare blow to positive news surrounding statins, a new study reveals the heart drugs are associated with a higher risk of diabetes in older women.

In a study of more than 150,000 diabetes-free women in their 50s, 60s and 70s, about 10,200 developed diabetes six or seven years after the investigation began. Forty-eight percent of the women taking statins were more likely to be diagnosed with diabetes than those not taking statins, according to the study.

Researchers told Reuters that they still aren’t sure why statins are linked to a diabetes risk. Statins’ effects on the muscles and liver could cause the body to make slightly more sugar than it normally would, or the drugs could cause users to exercise less, they suggested.

The study was published Monday in the Archives of Internal Medicine