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Introduction: Adverse changes in blood pressure (BP) over the life course can lead to adverse cerebrovascular outcomes, including reduced blood flow. In this life-course, longitudinal, population-based study, we investigated the link between midlife to late life changes in BP and cerebral blood flow (CBF) in old age.Methods: From the Age, Gene/Environment Susceptibility (AGES)–Reykjavik Study (2002-2011), 2491 individuals (mean age (SD): midlife 49.7 (6.1) and late-life 79.8 (4.7) years old) were included. BP was measured at three different time points: 1 in mid-life, and 2 in late-life measured 5 years apart (mean follow-up time 30.1 years). With linear mixed models, annual changes in BP were estimated for each participant (mmHg/year). Participants were categorized in tertiles of changes in systolic, pulse pressure and diastolic BP. Total CBF was measured in the last late-life visit with the Phase-Contrast MRI and standardized for brain parenchymal volume (mL/min/100mL).Results: Overall, each mmHg/year increase in systolic BP was associated with 3.2 mL/min/100 mL (95% CI: 0.7-5.7)) higher CBF. Mean (SE) CBF in low, middle and high tertiles of change in systolic BP were 56.0 (0.4), 56.6 (0.4) and 57.5 (0.4) mL/min/100mL respectively (P for trend: 0.01). A similar increase in total CBF was observed for an increase in pulse pressure: each mmHg/year increase in pulse pressure was associated with 6.3 mL/min/100mL (95% CI: 3.8-8.7) higher total CBF. In contrast, an increase in diastolic BP was linked with lower CBF: each mmHg/year increase in diastolic BP was associated with 6.3 mL/min/100mL (95% CI: 3.3-9.4) lower CBF. Mean (SE) CBF in low, middle and high tertiles of changes in diastolic BP were 57.3 (0.4), 57.3 (0.4) and 55.5 (0.4) mL/min/100mL respectively (P for trend: <0.001). All these associations were independent of sociodemographic and cardiovascular factors and antihypertensive medications.Conclusion: In an over 30 years of midlife to late-life follow up, we observed that individuals with increasing systolic BP and pulse pressure have higher CBF in old age. Conversely, increase in diastolic BP is associated with lower CBF. The mechanisms behind the link between long-term BP alterations and CBF need to be elucidated.