Nonlinear association between short-term ambient temperature and cognitive function in patients with ischaemic cerebrovascular disease: a retrospective repeated-measures cohort study

To characterise the association between short-term ambient temperature and cognitive performance in ischaemic cerebrovascular disease (ICVD), and whether it differs across cognitive groups. In this retrospective cohort, 730 patients with ICVD were enrolled and 618 completed four visits at 3-month intervals (0–9 months in the acute stream, 3–12 months in the non-acute stream); 571 participants (2,046 observations) were analysed. Cognitive function was assessed with the Montreal Cognitive Assessment (MoCA). Exposures were 7-day mean temperature (Temp_7d) and PM2.5. Temp_7d was modelled with restricted cubic splines (knots at 2.33, 18.29 and 28.92℃) and interacted with cognitive group in linear mixed-effects models with random intercepts and slopes, adjusting for demographics, vascular risk factors, depression, medication, season and PM2.5. Temperature effects used joint Wald tests; the three pairwise group contrasts were Bonferroni-corrected. Temp_7d showed an inverted U-shaped association with MoCA (χ 2 = 82.76, df = 2, P < 0.001). Predicted MoCA was maximal at 14.4 ℃; the model-derived near-peak range (within 0.1 points of the maximum, an arbitrary threshold) was 10.1–18.3 ℃. Relative to each group's peak (CN 14.2, MCI 14.7, VD 13.5 ℃), predicted MoCA at 28.92 ℃ was lower by 1.07 (95% CI 0.83–1.32), 1.45 (1.24–1.66) and 1.17 (0.88–1.47) points, and at 2.33 ℃ by 0.45 (0.27–0.64), 0.73 (0.57–0.89) and 0.39 (0.16–0.62). The global Temperature × Cognitive Group interaction was significant (χ 2 = 18.50, df = 4, P < 0.001): MCI differed from cognitively normal participants (adjusted P = 0.003), vascular dementia did not (adjusted P = 1.000), and a direct MCI-versus-vascular dementia contrast (adjusted P = 0.036) was sensitive to the number of spline knots. In this ICVD cohort, short-term ambient temperature showed an inverted U-shaped association with contemporaneous cognitive performance, with larger decrements at high than low temperatures and a stronger association in MCI; these observational findings require confirmation in prospective multicentre studies.