Racial Variation in Stroke Risk Among Women by Stroke Risk Factors

Background and Purpose- In the United States, black Americans exhibit a greater risk of stroke and burden of stroke risk factors than whites; however, it is unclear whether these stroke risk factors influence stroke risk differently across racial groups. Methods- In total, 126 018 participants of the Women's Health Initiative (11 389 black and 114 629 white women), free of stroke and coronary heart disease at baseline (1994-1998), were followed through 2010. Participants completed baseline clinical exams with standardized measurements of blood pressure and anthropometrics, medication inventory and self-reported questionnaires on sociodemographics, behaviors/lifestyle, and medical history. Incident total, ischemic and hemorrhagic strokes were updated annually through questionnaires with medical record confirmation. Rate differences (per 100 000 person-years) and hazard ratios (HR) based on multivariable Cox models and were estimated. Results- Over a median of 13 years, 4344 stroke events were observed. Absolute incidence rates were higher in black than white women in each age group. In age-adjusted analyses, the risk of stroke was significantly higher among black compared with white women (HR=1.47, 95% CI, 1.33-1.63); adjustment for stroke risk factors, which may be on the causal pathway, attenuated the estimate. Racial disparities were greatest among women 50 to <60 years (HR=3.48; 95% CI, 2.31-5.26; rate difference =99) and diminished with increasing age (60 to <70 HR=1.80; 95% CI, 1.50-2.16; rate difference =107; ≥70 years: HR=1.26; 95% CI, 1.10-1.43; rate difference =87; P_interaction <0.001). Black women 50 to <60 years remained at significantly higher risk than white women after adjustment for stroke risk factors (HR=1.76; 95% CI, 1.09-2.83). Conclusions- There was a moderately greater risk of total stroke among black compared with white women; however, racial disparities were greatest among women aged 50 to <60 years. Interventions targeted at younger black women may provide the greatest benefit in reducing disparities.