They've also found that mental disorders themselves have significant bone correlations. Dementia, schizophrenia and alcohol dependence are associated with reduced bone density. Depression is associated with less osteoporosis---which makes sense if you think that a lot of depression is due to low serotonin levels. Bipolar disorder and drugs other than alcohol were not found to have any correlation with osteoporosis.
Aside: FDA has released new warning that Tramadol (an opioid) increases suicide risk.