Combined effects of socioeconomic position, smoking, and hypertension on risk of ischemic and hemorrhagic stroke.

BACKGROUND AND PURPOSE Combined effects of socioeconomic position and well-established risk factors on stroke incidence have not been formally investigated. METHODS In a pooled cohort study of 68 643 men and women aged 30 to 70 years in Denmark, we examined the combined effect and interaction between socioeconomic position (ie, education), smoking, and hypertension on ischemic and hemorrhagic stroke incidence by the use of the additive hazards model. RESULTS During 14 years of follow-up, 3613 ischemic strokes and 776 hemorrhagic strokes were observed. Current smoking and hypertension were more prevalent among those with low education. Low versus high education was associated with greater ischemic, but not hemorrhagic, stroke incidence. The combined effect of low education and current smoking was more than expected by the sum of their separate effects on ischemic stroke incidence, particularly among men: 134 (95% confidence interval, 49-219) extra cases per 100 000 person-years because of interaction, adjusted for age, cohort study, and birth cohort. There was no clear evidence of interaction between low education and hypertension. The combined effect of current smoking and hypertension was more than expected by the sum of their separate effects on ischemic and hemorrhagic stroke incidence. This effect was most pronounced for ischemic stroke among women: 178 (95% confidence interval, 103-253) extra cases per 100 000 person-years because of interaction, adjusted for age, cohort study, and birth cohort. CONCLUSIONS Reducing smoking in those with low socioeconomic position and in those with hypertension could potentially reduce social inequality stroke incidence.