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Combined Effects of Socioeconomic Position, Smoking, and Hypertension on Risk of Ischemic and Hemorrhagic Stroke
Study Questions:
What is the combined effect and interaction between socioeconomic position (i.e., education), smoking, and hypertension on ischemic and hemorrhagic stroke incidence?
Methods:
In a pooled cohort study of 68,643 men and women ages 30-70 years in Denmark, the investigators examined the combined effect and interaction between socioeconomic position (i.e., 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, 3,613 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:
The authors concluded that reducing smoking in those with low socioeconomic position and in those with hypertension could potentially reduce social inequality stroke incidence.
Perspective:
This study reports that the combined effect of socioeconomic position and smoking exceeded the sum of their separate absolute effect on risk of ischemic stroke, particularly among men. Furthermore, there was an interaction between smoking and hypertension on risk of both ischemic and hemorrhagic stroke. Because both the prevalence and the effect of smoking and hypertension appear to be socially skewed, reducing smoking in the lower socioeconomic group and in those with hypertension may help reduce social inequality in risk of stroke.
Keywords: Stroke, Follow-Up Studies, Proportional Hazards Models, Research Personnel, Socioeconomic Factors, Risk Factors, Confidence Intervals, Hypertension, Smoking
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