In osteoporosis there is -
Osteoporosis occurs because of a defect in attaining peak bone mass and/or because of accelerated bone loss. In normal individuals, bone mass increases during skeletal growth to reach a peak between the ages of 20 and 40 years but falls thereafter (see Fig. 25.52). In women there is an accelerated phase of bone loss after the meno pause due to oestrogen deficiency, which causes uncou pling of bone resorption and bone formation, such that the amount of bone removed by osteoclasts exceeds the rate of new bone formation by osteoblasts. Agerelated bone loss is a distinct process that accounts for the gradual bone loss that occurs with advancing age in both genders. Bone resorption is not paicularly increased but bone formation is reduced and fails to keep pace with bone resorption. Accumulation of fat in the bone marrow space also occurs because of an agerelated decline in the ability of bone marrow stem cells to differentiate into osteoblasts and an increase in their ability to differentiate into adipocytes. Peak bone mass and bone loss are regulated by both genetic and environmental factors. Genetic factors account for up to 80% of the population variance in peak bone mass and other determinants of fracture risk, such as bone turnover and bone size. Polymorphisms have been identified in several genes that contribute to the pathogenesis of osteoporosis and many of these are in the RANK and Wnt signalling pathways, which play a critical role in regulating bone turnover (see Fig. 25.2, p. 1061). However, these account for only a small propor tion of the genetic contribution to osteoporosis and many additional genetic variants remain to be discovered. Environmental factors, such as exercise and calcium intake during growth and adolescence, are impoant in maximising peak bone mass and in regulating rates of postmenopausal bone loss. Smoking has a detrimental effect on bone mineral density (BMD) and is associated with an increased fracture risk, paly because female smokers have an earlier menopause than nonsmokers. Heavy alcohol intake is a recognised cause of osteoporo sis and fractures, but moderate intake does not substan tially alter risk. DAVIDSON'S PRINCIPLES OF PRACTICAL MEDICINE 22ND EDITION PAGE NO-690
Decrease in absolute amount of bone mass
More common in male
Radiographs show normal bone density
Hormonal replacement therapy
Endocrinology