Effect of Birth Cohort on Risk of Hip Fracture: Age-Specific Incidence Rates in the Framingham Study

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Abstract
Objectives. This study examined the effect of birth cohort on incidence rates of hip fracture among women and men in the Framingham Study. Methods. Age-specific incidence rates of first hip fracture were presented according to tertile of year of birth for 5209 participants of the Framingham Study, a population-based cohort followed since 1948. Sex-specific incidence rate ratios were calculated by Cox regression to assess the relation between birth cohort and hip fracture incidence. Results. An increasing trend in hip fracture incidence rates was observed with year of birth for women (trend, P = .05) and men (trend, P = .03). Relative to those born from 1887 to 1900 (incidence rate ratio [IRR] = 1.0), age-specific incidence rates were greatest in the most recent birth cohort, born from 1911 to 1921 (IRR = 1.4 for women, IRR = 2.0 for men), and intermediate in those born from 1901 to 1910 (IRR = 1.2 for women, IRR = 1.5 for men). Conclusions. Results suggest risk of hip fracture is increasing for successive birth cohorts. Projections that fail to account for the increase in rates associated with birth cohort underestimate the future public health impact of hip fracture in the United States.