Association of time of day at stroke onset with functional outcomes after reperfusion therapy in acute ischaemic stroke: a retrospective cohort study in China.
Night-onset stroke was associated with poorer functional outcomes at 3 months among patients receiving reperfusion therapy, with an adjusted OR of 1.55 (95% CI 1.07 to 2.22).
Key Findings
Results
Night-onset stroke was associated with a significantly higher risk of unfavourable 3-month functional outcome compared with day-onset stroke.
148 out of 286 patients (51.7%) in the night-onset group experienced unfavourable outcomes versus 182 out of 426 patients (42.7%) in the day-onset group
Unadjusted OR 1.44 (95% CI 1.06 to 1.94), p=0.018
Multivariable adjusted OR 1.55 (95% CI 1.07 to 2.22), p=0.019
Day-onset was defined as 06:00–18:00 and night-onset as 18:00–06:00
Unfavourable outcome was defined as modified Rankin Scale score of 3–6 at 3 months
Results
The association between night-onset stroke and unfavourable outcomes remained significant across multiple statistical adjustment methods.
Propensity score matching (PSM): OR 1.45 (95% CI 1.01 to 2.08), p=0.044
Inverse probability of treatment weighting (IPTW): OR 1.42 (95% CI 1.02 to 1.96), p=0.036
Overlap weighting (OW): OR 1.42 (95% CI 1.03 to 1.96), p=0.032
Consistency across PSM, IPTW, OW, and multivariable adjustment strengthens the robustness of the finding
Results
Stroke onset during the 22:00–02:00 time window was associated with the highest likelihood of unfavourable outcome among all 4-hour intervals examined.
Adjusted OR 2.44 (95% CI 1.34 to 4.43), p=0.003 for the 22:00–02:00 interval
Patients were also categorised into six groups by 4-hour intervals to examine time-of-day effects more granularly
This interval showed a notably stronger association than the overall night-onset group estimate
Methods
The study included 712 patients with acute ischaemic stroke who received reperfusion therapy at a single centre in China over approximately 3.5 years.
Data collected between October 2018 and March 2022
Reperfusion therapy included intravenous thrombolysis or combined endovascular therapy
286 patients were in the night-onset group and 426 in the day-onset group
Study design was a retrospective cohort study
Registered in the Chinese Clinical Trial Registry: ChiCTR2500101844
Methods
The primary outcome measure was 3-month functional status evaluated using the modified Rankin Scale, dichotomised into favourable (scores 0–2) and unfavourable (scores 3–6) outcomes.
Modified Rankin Scale scores of 0–2 were classified as favourable outcomes
Modified Rankin Scale scores of 3–6 were classified as unfavourable outcomes
Functional status was assessed at 3 months post-stroke
What This Means
This research suggests that the time of day when a stroke occurs may influence how well patients recover, even when they receive clot-busting or clot-removing treatments. Among 712 stroke patients in China who received reperfusion therapy (treatments designed to restore blood flow to the brain), those whose strokes began at night (between 6 PM and 6 AM) were about 55% more likely to have a poor functional outcome three months later compared to those whose strokes began during the day. The worst outcomes were seen in patients whose strokes began between 10 PM and 2 AM, who were more than twice as likely to have poor outcomes.
The researchers used several different statistical methods to account for differences between the day-onset and night-onset patient groups, and the association held up consistently across all approaches. This suggests the finding is not simply explained by differences in patient characteristics between the two groups. However, because this was a single-center retrospective study — meaning it looked back at existing records from one hospital — it cannot definitively prove that nighttime onset causes worse outcomes.
This research suggests that biological factors related to time of day, such as circadian rhythms affecting brain physiology or stroke severity, or practical factors like delays in recognizing and treating strokes that occur at night, may play a role in stroke recovery. The authors call for larger, multi-center prospective studies to confirm these findings and to better understand why time of onset might matter, which could eventually help improve care strategies for patients who suffer strokes at night.
Wang Y, Fan S, Huang S, Lu M, Yang Y, Lu H, et al.. (2026). Association of time of day at stroke onset with functional outcomes after reperfusion therapy in acute ischaemic stroke: a retrospective cohort study in China.. BMJ open. https://doi.org/10.1136/bmjopen-2026-119656