Epidemiology worldwide

Osteoporosis is a global problem that will increase in significance with the growing elderly population. The condition affects both sexes and all races, albeit to different degrees. Fractures represent the main clinical manifestation of osteoporosis, but fractures have other determinants (eg, risk factors for failing) that are external to the skeleton [1]. Osteoporosis is generally assessed in vivo by measuring bone mineral density (BMD). Although not completely representative of the bone architecture changes that are responsible for skeletal fragility (see article by Seeman in this issue), BMD is strongly correlated with bone strength in vitro and is a good predictor of future fracture risk, as reviewed by Miller in this issue. Because the relationship between bone density and fracture risk is a continuous one, like that between blood pressure and stroke, the choice of a BMD value to define osteoporosis is necessarily somewhat arbitrary. In 1994, the World Health Organization (WHO) defined osteoporosis operationally to be a femoral neck BMD value 2.5 standard deviations (SD) or more below the mean for normal young white women, or a t score of -2.5 [2]. Using this definition, it is possible to assess the prevalence of osteoporosis in different populations, and the increasing availability of bone densitometry has permitted such studies to be performed in various regions around the world. This article reviews the epidemiology of osteoporosis as it relates to age, gender, ethnicity, and other risk factors and makes projections for the future as populations continue to age worldwide.