Parathyroid Hormone in the Pathophysiology of Osteoporosis

While parathyroid hormone (PTH) excess syndromes are clearly associated with bone loss, the issue of whether physiological changes in PTH secretion following the menopause or with aging also contribute to the pathogenesis of osteoporosis is somewhat unclear and the focus of considerable attention. In the early postmenopausal period, PTH appears to be responding to the estrogen deficiency-induced changes in bone turnover rather than driving these changes. PTH levels do, however, increase with age in women and in men, primarily after the age of 70 years. This secondary hyperparathyroidism of aging is associated with increased bone turnover, particularly in women, and with rates of bone loss in elderly individuals. Given the evidence that PTH can increase cortical porosity, the observation that cortical porosity increases markedly with age has led to the speculation that age-related increased PTH secretion may be responsible for this increase in cortical porosity. However, further studies are needed to better define the contribution of increased PTH concentrations towards bone loss in the elderly, particularly age-related changes in cortical bone.