Diurnal variation in neurovascular coupling and the impact of sleep quality: a UK Biobank study

The observed reduction in NVC in the late morning and its association with objective measures of impaired sleep quality suggest a potential role for endothelial dysfunction, potentially contributing to the associated increased cerebrovascular risk. Statement of Significance Cerebrovascular fluctuations with time-of-day and with sleep quality could offer insights into stroke mechanisms. This study provides the first large-scale evidence that neurovascular coupling (NVC), a functional marker of cerebrovascular health, follows a diurnal pattern characterized by a reproducible midday dip independent of age, sex, and vascular risks. This suggests a period of potential vulnerability in the cerebral blood supply. Furthermore, a history of stroke and sleep disorders such as sleep apnea are associated with impaired NVC, indicating a disruption of the brain's natural rhythms. These findings highlight translational opportunities to optimize sleep and align preventive strategies with diurnal physiology to reduce cerebrovascular risk. Remaining knowledge gaps include the need for 24-h assessments and longitudinal studies to clarify causal pathways.