The study, published in the Journal of Clinical Oncology, found 78 percent of breast cancer survivors had at least one other cause of bone loss -- such as vitamin D deficiency.

"Doctors evaluating breast cancer patients for possible bone loss should look further than cancer drugs," lead author Dr. Pauline Camacho of the Loyola University Stritch School of Medicine in Chicago said in a statement.

The study authors suggest that while cancer drugs do cause bone loss, cancer survivors, as in the normal population, also suffer bone loss due to treatable causes and deserve a thorough bone health evaluation.

The researchers reviewed the charts of 238 post-menopausal patients with lower than normal bone mineral density referred to the Loyola's Osteoporosis and Metabolic Bone Disease Center from 2000 to 2006. Among the patients were 64 women with breast cancer.

Thirty-eight percent of the breast cancer patients had vitamin D deficiency, compared with 51 percent of the non-breast cancer patients. Excessive calcium excretion in urine was found in 16 percent of cancer patients and 8 percent of non-cancer patients.