Background: Stroke risk is greater in South Asians than Europeans. We sought to compare associations between blood pressure (BP) and stroke by ethnicity and determine how BP contributes to ethnic differences in disease.

Methods: Population sample of 1510 European and 1195 South Asian men recruited between 1988–1991, mean age 52±7yrs. Incident fatal and non-fatal strokes were captured over 20 years of follow-up. Cox models demonstrated associations between mean arterial BP (MAP) and stroke.

Results: South Asians had more incident strokes than Europeans (5.6 (4.7,6.7) versus 4.7 (4.0,5.6) per 1000 person years, age-adjusted hazard ratio:1.40 (1.08,1.76), p=0.01) and higher MAPs than Europeans (97±12 versus 93±12mmHg, p<0.0001).

MAP was more strongly associated with stroke in South Asians than Europeans, (HR (95% CI): 1.59(1.35,1.86) versus 1.19(1.00,1.43) respectively, ethnicity interaction p=0.03), even accounting for receipt of anti-hypertensive medication (1.57(1.32,1.86 versus 1.10(0.91,1.32), interaction p=0.03). The ethnic difference in impact of MAP diminished after further adjustment for smoking, waist circumference, HDL, fasting glucose, HOMA2-IR, HbA_1c and heart rate (1.40(1.12,1.75) versus 1.15(0.92,1.42), interaction p=0.24). However, the greater effect of MAP on stroke in South Asians persisted when this latter model was restricted to people not receiving anti-hypertensive medications, (1.57(1.26,1.96) versus 1.08(0.85,1.37), interaction p=0.02).

Adjustment for MAP could not account for the excess stroke risk in South Asians (1.27 (1.00, 1.62) p=0.05), nor could other risk factors.

Conclusions: MAP had a greater impact on stroke risk in South Asians than Europeans, but could not account for their excess stroke risk, alone or in conjunction with additional risk factors.