Post-menopausal osteoporosis and the resulting fractures are an important cause of disability and loss of independence. They also increase the risk of morbidity and mortality.

Given potential side effects, hormone replacement therapy is no longer recommended for menopausal women with risk of becoming osteoporotic. The very significant decrease in the use of these treatments is suspected of contributing to a resurgence in the incidence of osteoporotic fractures, particularly in women before the age of 70. There is a need for prevention of osteoporosis.

Mother-of-pearl is a candidate for long-term use due to the combination of its effects: calcium supplementation, anti-resorptive activity and osteoanabolic activity.

Our hypothesis is that powdered mother-of-pearl supplementation limits bone loss in postmenopausal women with risk of becoming osteoporotic.

Inclusion Criteria:

• Post-menopausal women (50-65y) with risk of becoming osteoporotic
• T-score between -1 and -3
• Absence of fragility fractures history

Exclusion Criteria:

• absence of parathyroid glands (phospho-calcic regulation)
• presence of kidney stones
• patients who follow a treatment that could interfere with bone metabolism (corticotherapy, menopausal hormonal therapy, anti-oestrogen treatment, non-controlled hyperthyroiditis, hyper- and hypothyroiditis)
• bone diseases (Paget'disease, osteomalacia)
• chronic alcoholism

Stratified randomization :

The study will be double-blinded to avoid follow-up bias and assessment bias. The maintenance of the blind will be guaranteed by the fact that the capsules of mother-of-pearl will be indistinguishable from those of CaCO3 (same shape, same color, same weight). Only the internal use pharmacies (IUP) of each center will be open, for the attribution of the treatment.