Background: Stroke is a major cause of death and disability in most populations of eastern Asia, and the incidence, particularly of haemorrhagic stroke, is generally higher than in western populations. This study aimed to assess the contributions of blood pressure and blood cholesterol concentrations to stroke risk in populations from eastern Asia.
Methods: The project included 13 cohorts from the People's Republic of China and five from Japan (124,774 participants, 837,214 person-years of observation). All 18 cohorts provided data on blood pressure and 12 (69,767 participants) provided data on cholesterol concentrations. Parametric and non-parametric analyses were done, with adjustments for several potential confounding factors. Analyses were based on estimated usual diastolic blood pressure and cholesterol concentration during follow-up, rather than baseline measurements, to avoid regression dilution bias.
Findings: Overall mean blood pressure was 124/78 mm Hg and mean cholesterol concentration was 4.5 mmol/L. 1798 strokes occurred; 751 (42%) were classified as haemorrhagic and 707 (39%) were confirmed by computed tomography or necropsy. Each 5 mm Hg lower usual diastolic blood pressure was associated with lower risk of non-haemorrhagic stroke (odds ratio 0.61 [95% CI 0.57-0.66]) and lower risk of haemorrhagic stroke (0.54 [0.50-0.58]). With decreasing cholesterol concentrations there were trends towards a decrease in risk of non-haemorrhagic stroke (odds ratio for 0.6 mmol/L decrease, 0.77 [0.57-1.06]) and an increase in risk of haemorrhagic stroke (1.27 [0.84-1.91]). Overall, there was no clear evidence of any interaction between cholesterol and diastolic blood pressure.
Interpretation: Blood pressure is an important determinant of stroke risk in eastern Asian populations, whereas cholesterol concentration is less important, affecting the proportions of stroke subtypes more than overall stroke numbers. The association between blood pressure and stroke seems stronger than in western populations; a population-wide reduction of 3 mm Hg in diastolic blood pressure should eventually decrease the number of strokes by about a third.