Mind over Matter: how depression causes bone loss through nerve activation.

The chronic activation of the arousal part of our autonomic nervous system (the sympathetic nervous system) that can occur during stress has been shown to cause an array of degenerative effects. Yirmiya et al, using a mouse model system, now link this system to the low bone mass and increased incidence of osteoporotic fractures associated with major depression. They show that mice subjected to chronic mild stress (CMS) show behavioral depression and impaired bone mass and structure. Antidepressant therapy, which prevents the behavioral responses to CMS, completely inhibits the decrease in bone formation and markedly attenuates the CMS-induced bone loss. The depression-triggered bone loss is associated with a substantial increase in bone norepinephrine levels and can be blocked by the beta-adrenergic antagonist propranolol, suggesting that the sympathetic nervous system mediates the skeletal effects of stress-induced depression. These results demonstrate an interaction among behavioral responses, the brain, and the skeleton, which leads to impaired bone structure. This suggests that depression is a potential major risk factor for osteoporosis in the aging population.