Oxytocin is a neurohypophysial hormone involved in several central and peripheral functions including parturition, milk let-down reflex and social behaviour. In vitro and animals studies have shown growing evidence that oxytocin plays a role in bone remodeling and osteoporosis. The investigators have previously show in a small sample of post-menopausal women with severe osteoporosis (n=20) compare to healthy control (n=16) that oxytocin serum level is significantly decreased, independently of leptin and estradiol, that are known to modulate oxytocin secretion. Thus, oxytocin appears as a new interesting factor in the osteoporosis pathophysiology. The aim of the present study is to confirm the relationships between bone status, evaluated by bone mineral density and prevalent fragility fractures, body composition and oxytocin serum levels on a large population. The investigators will also determine if the relationship between bone mineral density and oxytocin is independent of estradiol and leptin in this population and evaluate the relationships between oxytocin serum level and co-morbidities such as cardiovascular diseases, depression and dementia. Theses analysis will be done on the serum already available of 1000 women of the international OPUS cohort. Bone mineral density, body composition analysis by Dual energy X-ray Absorptiometry (DXA), estradiol and clinical data are already available. The investigators will select women, aged from 55 to 79 y at the time of inclusion.
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