Association between extreme temperature events and multimorbidity among older adults: evidence from the CHARLS

BACKGROUND: The older adults are a high-risk group for multimorbidity. However, a possible multimorbidity link with extreme temperature events is unknown. We aimed to explore the association of cold spells and heatwaves and risk of multimorbidity among older people. METHODS: This cohort included 9475 adults aged 45 and over from the China Health and Retirement Longitudinal Study (CHARLS). Heatwaves and cold spells were defined according to the average temperature, with the combination of six thresholds (≥ 97.5%, 97.5%, 92.5%, 7.5%, 5%, and 2.5%) and three durations (≥ 2, 3, and 4 days). Our outcome variable was multimorbidity, defined as the coexistence of two or more chronic diseases in individuals. Cox proportional hazard models with time-dependent covariates were employed to assess effects of extreme temperature events on the risk of multimorbidity. We also conducted subgroup analyses to assess possible modifying effects among various populations. RESULTS: Heatwaves were positively associated with the risk of multimorbidity, with HRs ranging from 1.008 (95% CI: 1.002-1.013) to 1.021 (95% CI: 1.007-1.035). Besides, each additional day of cold spell exposure was correlated with an increased risk of multimorbidity by between 1.8% (HR: 1.018, 95% CI: 1.012-1.024) and 2.4% (HR: 1.024, 95% CI: 1.016-1.032) among older adults. The subgroup analyses revealed that males, adults with insufficient sleep, or living in southern areas were more susceptible to the extreme temperature events. CONCLUSIONS: Both cold spells and heatwaves exposure increase the risk of multimorbidity in older adults. Our findings highlight the necessity of preventing harmful effects of extreme temperature events.