The impact of cold spells and heat waves frequencies on the prevalence and incidence of stroke in middle-to-elderly age population in China: evidence from the China Health and Retirement Longitudinal Study (CHARLS).

Stroke, a key cardiovascular disease, is impacted by cold spells and heat waves. However, limited sample size and unclear impact on the aging population's prevalence and incidence remain concerns. We aim to explore the association between cold spells and heat waves frequency and stroke in middle-aged and elderly people in China. Utilizing data from the China Health and Retirement Longitudinal Study (CHARLS), this study conducted cross-sectional (16,766 participants aged 45 and above in 2011) and longitudinal analyses (tracked 15,215 stroke-free participants from 2011 to 2018). Cold spells and heat waves are defined by temperature thresholds and duration for a given community. The stroke cases were identified through self-reports. Logistic regression, Cox proportional-hazards model and time-varying Cox proportional hazards regression model were employed in our analysis. In the cross-sectional study, 469 (2.8%) participants suffered stroke. Every 1 event increased in cold spells frequency (OR: 1.205, 95% CI: 1.067,1.361) and heat waves frequency (OR: 1.087, 95% CI: 1.017,1.162) was positively associated with stroke prevalence. In the cohort study, 1,028 (6.8%) developed stroke during an average follow-up of 6.3 years. We observed consistent adverse effects of cold spells on stroke incidence (HR: 1.149, 95% CI: 1.062, 1.243), whereas heat waves showed no significant association. Considering exposure changes during follow-up, both cold spells and heat waves significantly increased stroke incidence. Subgroup analyses showed a significant interaction between heat waves and geographic location, which indicated northern residents exhibited higher risks. Our study suggests that cold spells elevate stroke risk among middle-aged and older Chinese adults. Meantime, the impact of heat waves on stroke incidence is also worth noting for northern residents. This finding provides evidence of temperature fluctuation's impact on this cardiovascular event in the nationwide population, suggesting temperature-control optimization could be an effective disease-control measure.