Prevalence of osteoporotic bone mineral density at the hip in Britain differs substantially from the US over 50 years of age: implications for clinical densitometry

The purpose of this study was to compare hip bone mineral density (BMD) recorded in seven population based cohorts in Britain with the third National Health and Nutrition Examination Survey (NHANES III) US population-based reference data, in order to assess geographic variation in the prevalence of osteoporosis. Men and women aged 50-80+ years were randomly recruited from population and health registers. Dual X-ray absorptiometry (DXA) equipment was used to measure BMD at the hip, with the femoral neck and the trochanter regions studied. Prevalences of osteopenia and osteoporosis were estimated in accordance with World Health Organisation diagnostic criteria for women. Young normal data, used to establish cut-off criteria, was from NHANES III. Both male and female British subjects over 50-years-old were found to have significantly higher mean BMD at the femoral neck and trochanter than their US counterparts. Decline in BMD with age in British men appeared slower than in US men. Between British centres there were also statistically significant differences in BMD values in both sexes. British age-adjusted prevalences of osteopenia in women averaged 20% less than those of NHANES III, whereas the prevalence of osteoporosis was substantially lower in British subjects of both sexes (55% in women, 68% in men). Thus, applying the US NHANES III data as the referent, osteoporosis of the proximal femur in Britain appears to be less common than in the US, due primarily to differences in the lower tails of the BMD distributions. Providing that the relationship between fracture rates and BMD is the same in Britain and the US, it would still be appropriate to apply the reference data in fracture risk assessment in the UK.