Researchers at the National Institute of Mental Health (NIMH) and the National Institutes of Health (NIH) have determined that depression puts pre-menopausal women at a higher risk of developing osteoporosis. Even mild depression results in a lower level of bone mass in comparison to non-depressed pre-menopausal women. The research showed the risk of developing osteoporosis from depression is at least as high as the other known risk factors for osteoporosis, which among others are smoking, low calcium intake, and lack of physical activity. Osteoporosis is a degenerative bone disease, where over time the bone density of a patient is slowly reduced. This results in an increased risk of bone fracture. In advanced stages of the disease simple daily movements can already lead to fractures. Some fractures can lead to the patient's death.

A person's bone mass is at its highest in youth. Then the bone-thinning process begins and lasts throughout a person's entire life. For women, the bone-thinning process greatly accelerates after menopause. Thus, post-menopausal women are in the highest risk group for developing osteoporosis. The scientists studied 89 depressed and 44 non-depressed women. These women were pre-menopausal, well nourished, and between the ages of 21 to 45. Both groups had similar risk factors in regards to osteoporosis like calcium, caffeine, and alcohol intake, as well as smoking, physical activity, birth control, and age of first menstrual period. The bone mass of each woman was measured through DXA scanning, which is an X-ray technique.

Already in preliminary studies scientists were able to consider depression as a cause of lower than normal bone mass in pre-menopausal women. The depressed women involved in this study were on antidepressant medications. While previous studies indicated an increase in bone fractures in older adults, who take selective serotonin reuptake inhibitors (a type of antidepressant medication), this study revealed no link between antidepressant medications and bone mass loss in pre-menopausal women. According to the scientists, the hipbones are the part of the body most often fractured in older people. This is also the area, where depressed pre-menopausal women showed the greatest loss of bone mass. In fact, seventeen percent of the depressed women enrolled in the study showed lower than normal bone mass in the most vulnerable part of the hip, the femoral neck. Only two percent of the women in the non-depressed group showed bone thinning in this particular area. Furthermore, twenty percent of the women in the depressed group showed bone thinning in the lumbar spine and lower back, compared to nine percent in the non-depressed group.

Therefore, depression does put pre-menopausal women at an increased risk of osteoporosis. However, the degree of depression and number of depressive episodes does not appear to significantly increase the rate of the bone loss. The scientists also examined the women's blood and urine samples taken every hour for a full day. They found that the depressed women show imbalances in the substances of their immune system, including inflammation-causing substances. The inflammation-promoting protein levels were higher in the depressed women, with the preventing protein levels being lower. IL-6 is an inflammation-promoting protein, which is known to advance bone loss.

The scientists see this as evidence of the depression causing the immune system imbalances, which as a result accelerates the bone loss. According to the researchers excess adrenalin may cause the imbalance through over-stimulation of the immune system. Adrenalin production is usually over-active in the depressed. As a result of the study showing a link between depression and a higher risk of osteoporosis, depression in pre-menopausal woman should be seen as a 'red flag.' Physicians should look for signs of osteoporosis in order to start treatment as early as possible to prevent accelerated bone loss and bone fractures.