'Skeletal Age' is defined as the age of the skeleton resulting from fractures or exposure to risk factors that elevate the risk of fracture. Excessive bone loss is associated with an increased risk of fracture. This study sought to use the skeletal age to quantify the impact of bone loss on mortality.
We analyzed data from the Study of Osteoporosis Fractures (SOF) and Osteoporotic Fractures in Men (MrOS). Bone mineral density (BMD) at the femoral neck was measured at baseline and subsequent visits, and this analysis was limited to those with at least 3 BMD measurements (n=3848 women and n=2925 men). Mortality was ascertained from death certificates and hospital records. The association between BMD change and mortality was assessed by a multivariable Cox’s proportional hazard model, adjusting for age, body mass index, smoking status, alcohol consumption, and dietary calcium intake. The magnitude of association between bone loss and mortality was converted to years of life lost using Gompertz's law of mortality and the US life table. Skeletal age was determined as the sum of chronological age and years of life lost for each individual.
The average annual percent of change in BMD was -0.62±1.2%(mean±SD) in women and -0.16±0.9% in men. During the study period, 1942 women and 1949 men died. For the same rate of bone loss, men experienced a high risk of death than women. Each SD increase in bone loss was associated with a 1.2-fold (95%CI,1.1-1.3) in women and 1.4-fold (95%CI,1.3-1.5) in men after adjusting for age, baseline FNBMD, BMI, smoking and drinking status. Specifically, a 70-year-old individual with BMD loss exceeding 2% would have skeletal age of 74.6years in women and 75.9years in men. These data indicate that excess femoral neck bone loss is associated with an increased loss of years of life and accelerated bone fragility.