Background American and European guidelines define hypertension differently and are sex agnostic. Our aim was to assess the impact of different hypertension thresholds at the age of 40 on 30-year stroke risk and to examine sex differences.Methods We included 2608 stroke-free individuals from the Akershus Cardiac Examination 1950 Study, a Norwegian regional study conducted in 2012–2015 of the 1950 birth cohort, who had previously participated in the Age 40 Program, a nationwide health examination study conducted in 1990–1993. We categorised participants by systolic blood pressure (SBP) at age 40 (<120 mm Hg (reference), 120–129 mm Hg, 130–139 mm Hg and ≥140 mm Hg) and compared stroke risk using Cox proportional hazard regressions adjusted for age, sex, smoking, cholesterol, physical activity, obesity and education. Fatal and non-fatal strokes were obtained from the Norwegian Cardiovascular Disease Registry from 1 January 2012 to 31 December 2020, in addition to self-reported strokes.Results The mean age was 40.1±0.3 years (50.4% women) and mean SBP was 128.3±13.5 mm Hg (mean±SD). Stroke occurred in 115 (4.4%) individuals (32 (28%) women and 83 (72%) men) during 29.4±2.9 years of follow-up. SBP between 130 and 139 mm Hg was not associated with stroke (adjusted HR 1.71, 95% CI 0.87 to 3.36) while SBP ≥140 mm Hg was associated with increased stroke risk (adjusted HR 3.11, 95% CI 1.62 to 6.00). The adjusted HR of stroke was 4.32 (95% CI 1.66 to 11.26) for women and 2.66 (95% CI 1.03 to 6.89) for men, with non-significant sex interactions.Conclusions SBP ≥140 mm Hg was significantly associated with 30-year stroke risk in both sexes. A small subgroup of women had SBP ≥140 mm Hg and systolic hypertension was a strong risk factor for stroke in these women.Trial registration number NCT01555411.
