Pathogenesis of Osteoporosis

In women an age-related slow decrease is accelerated to an acute loss of bone in the menopausal and postmenopausal periods, and then followed by a gradual and progressive decline in bone mineral density (BMD) with age. In men, bone loss begins somewhat later, but it is due, as in women, to increased osteoclastic resorption, which is a direct consequence of decreases in steroid hormones, i.e. hypogonadism. The decrease in steroid hormones also directly impacts cells which have the oestrogen receptors alpha or beta such as the bone marrow mesenchymal progenitor cells responsible for the production of osteoblasts and adipocytes. Oestrogen promotes osteoblastogenic differentiation and inhibits adipogenesis. Therefore, with advancing age, bone formation is decreased as a direct consequence of a shift in the balance of production of the two cell lineages, in favour of adipocytes.