The effect of age and bone mineral density on the absolute, excess, and relative risk of fracture in postmenopausal women aged 50-99: results from the National Osteoporosis Risk Assessment (NORA).

INTRODUCTION: This study evaluates the effect of age and bone mineral density (BMD) on the absolute, excess, and relative risk for osteoporotic fractures at the hip, wrist, forearm, spine, and rib within 3 years of peripheral BMD testing in postmenopausal women over a wide range of postmenopausal ages.
METHODS: Data were obtained from 170,083 women, aged 50-99 years, enrolled in the National Osteoporosis Risk Assessment (NORA) following recruitment from their primary care physicians' offices across the United States. Risk factors for fracture and peripheral BMD T-scores at the heel, forearm, or finger were obtained at baseline. Self-reported new fractures at the hip, spine, rib, wrist, and forearm were obtained from questionnaires at 1- and 3-year follow-ups. Absolute, excess (attributable to low BMD), and unadjusted and adjusted relative risks of fracture were calculated.
RESULTS: At follow-up, 5312 women reported 5676 fractures (868 hip, 2420 wrist/forearm, 1531 rib, and 857 spine). Absolute risk of fracture increased with age for all fracture sites. This age-effect was most evident for hip fracture--both the incidence and the excess risk of hip fracture for women with low BMD increased at least twofold for each decade increase in age. The relative risk for any fracture per 1 SD decrease in BMD was similar across age groups (p>0.07). Women with low BMD (T-score <-1.0) had a similar relative risk for fracture regardless of age.
CONCLUSIONS: At any given BMD, not only the absolute fracture risk but also the excess fracture risk increased with advancing age. Relative risk of fracture for low bone mass was consistent across all age groups from 50 to 99 years.