Background: Between the ages 45 and 65 years, incident stroke is 2 to 3 times more common in blacks than in whites, a difference not explained by traditional stroke risk factors.
Methods: Stroke risk was assessed in 27 748 black and white participants recruited between 2003 and 2007, who were followed up through 2011, in the REasons for Geographic And Racial Differences in Stroke (REGARDS) study. Racial differences in the impact of systolic blood pressure (SBP) was assessed using proportional hazards models. Racial differences in stroke risk were assessed in strata defined by age (<65 years, 65-74 years, and ≥75 years) and SBP (<120 mm Hg, 120-139 mm Hg, and 140-159 mm Hg).
Results: Over 4.5 years of follow-up, 715 incident strokes occurred. A 10-mm Hg difference in SBP was associated with an 8% (95% CI, 0%-16%) increase in stroke risk for whites, but a 24% (95% CI, 14%-35%) increase for blacks (P value for interaction, .02). For participants aged 45 to 64 years (where disparities are greatest), the black to white hazard ratio was 0.87 (95% CI, 0.48-1.57) for normotensive participants, 1.38 (95% CI, 0.94-2.02) for those with prehypertension, and 2.38 (95% CI, 1.19-4.72) for those with stage 1 hypertension.
Conclusions: These findings suggest racial differences in the impact of elevated blood pressure on stroke risk. When these racial differences are coupled with the previously documented higher prevalence of hypertension and poorer control of hypertension in blacks, they may account for much of the racial disparity in stroke risk.