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.

Inclusion Criteria:

• post-menopausal women,
• able to undergo bone density,
• without cognitive limitation,
• Age at the time of inclusion: 55 -79y,
• Written consent.

Exclusion Criteria:

• Individuals were excluded because of inability to undergo bone densitometry or perform specified investigations or because of cognitive limitations

OPUS is a prospective study of postmenopausal women recruited in the general population between April 1999 and April 2001 from five European centers (Aberdeen (UK), Berlin (Germany), Kiel (Germany), Paris (Hôpital Cochin, France), and Sheffield (UK)). Investigations were approved at each institution according to the Declaration of Helsinki. Written consent was obtained from all subjects. Each center recruited approximately 500 postmenopausal women comprising 100 individuals in each 5-yr age band between 55 and 79. Ninety-nine percent of subjects were of white ethnicity.