Extreme temperature events and frailty progression in middle-aged and older adults: the longitudinal evidence from CHARLS

With global climate change, extreme temperature events (ETEs) are becoming more frequent and lasting longer, including heatwaves (HW) and cold spells (CS). ETEs have negative effects on human health, but its association with frailty progression is unclear. This study utilized data from the China Health and Retirement Longitudinal Study (CHARLS) from 2015 to 2018. Frailty was assessed by the Frailty Index (FI), which is calculated using 32 items. ETEs were identified based on temperature thresholds and durations, quantified by event and day counts. The association between ETEs and FI was assessed by the difference-in-difference (DiD) method compared between baseline (2015) and follow-up (2018). Generalized linear models (GLMs) examined the association between ETEs exposure and frailty progression. The study included 4,955 middle-aged and older participants (mean age 60.97 ± 8.82 years, 52.7% women). CS exposure was positively correlated with FI, whereas HW exposure was not. DiD analysis showed that under the CS definition (5th percentile, ≥4days duration), exposure to days (β = 0.802, 95% CI: 0.49 to 1.114, p < 0.001, in model 3) and exposure to events (β = 5.635, 95% CI: 3.276 to 7.995, p < 0.001, in model 3) were associated with FI progression during the follow-up period. As the temperature threshold for CS decreases and the duration increases, the estimates of the transitions from robust to pre-frail and frail states gradually strengthen. For ETEs exposure, CS exposure increases the risk of frailty progression in middle-aged and older adults.