Background The biological consequences of stress from the social environment pattern health outcomes. This study investigated whether social stress is prospectively associated with fracture incidence among racially and ethnically diverse, postmenopausal women.

Methods Data from 160 709 postmenopausal women in the Women’s Health Initiative was analysed using Cox proportional hazards regression models to examine prospective associations of social stress with time to total and hip fracture incidence. Self-reported questionnaires measuring social strain, social functioning and social support were used to assess social stress.

Results Age and race/ethnicity modified associations between social stress and total and hip fractures. HRs for the associations between higher social support (indicating lower social stress) and total fractures among those age 50–59 years were 0.92 (95% CI: 0.90 to 0.94); HR=0.94 (95% CI: 0.93 to 0.95) for those age 60–69 years and HR=0.96 (95% CI: 0.95 to 0.98) for those age 70–79 years. Higher social strain was associated with greater hip fracture incidence among Native American women (HR=1.84, 95% CI: 1.10 to 3.10), Asian women (HR=1.37, 95% CI: 1.01 to 1.86) and white women (HR=1.04, 95% CI: 1.01 to 1.08).

Conclusion Identifying population patterns of fracture incidence as biological expressions of social environments reveals how race/ethnic specific social environmental factors influence disparities in fractures.