Do men and women fracture bones at similar bone densities?

When the World Health Organization (WHO) guidelines for the definition of osteoporosis in postmenopausal women were identified similar proposals were not developed for men as there was insufficient evidence about the relationship between bone density and fracture in men. We have therefore examined the relationship between bone density and vertebral fracture in men and women attending for assessment of possible osteoporosis. Two hundred and sixty-four women (age 64 [SD 10] years) and 37 men (age 55 [10] years) were studied. Bone density was measured in the lumbar spine and femoral neck by dual-energy X-ray absorptiometry and expressed both as bone mineral density (BMD; g/cm2) and as T-scores. In both sexes there was a sigmoid relationship between the cumulative frequency of vertebral fracture and bone density at both sites. There was a linear relationship between the log odds of fracture and bone mass for both sexes and both sites (r = 0.97-0.99; p < 0.0001). The slope of these lines was significantly steeper for men than women. The BMD at which there was 50% risk of fracture was higher in men than women (0.908 vs 0.844 g/cm2). The difference between the slopes was similar when the bone mass was expressed as a T-score. However, the T-score associated with 50% prevalence of fracture was similar in the two sexes (F: -2.77 vs M: -2.60). We conclude that although there is a different relationship between bone density and fracture in the two sexes the current WHO definition of osteoporosis in postmenopausal women can be appropriately applied to men.