Association between extreme temperature events and intrinsic capacity trajectories among middle-aged and older adults: the China Health and Retirement Longitudinal Study (CHARLS).

BACKGROUND

Global climate change has increased the frequency, intensity, and duration of extreme temperature events, while population aging poses unprecedented public health challenges. However, the association between extreme temperature events and longitudinal trajectories of intrinsic capacity (IC)-a multidimensional construct proposed by the World Health Organization as a core indicator of healthy aging-remains unknown.

METHODS

Data were drawn from 1,393 participants aged 45-80 years who had complete IC assessments across three waves (2011, 2013, 2015) of the China Health and Retirement Longitudinal Study (CHARLS). IC was operationalized as a composite score (range 0-10) spanning locomotion, sensory, vitality, psychological, and cognition domains. K-means clustering identified heterogeneous IC trajectories. Extreme temperature events were defined using city-specific daily apparent temperature (heatwave: ≥95th percentile for ≥ 3 days; cold spell: ≤5th percentile for ≥ 3 days). Multinomial logistic regression examined associations between cumulative heatwave days (2011-2015) and IC trajectory membership, adjusting progressively for sociodemographic, lifestyle, and health-related covariates.

RESULTS

Three IC trajectories were identified: High-stable (41.3%), Moderate-declining (26.4%), and Low-declining (32.3%). Each additional heatwave day significantly increased the risk of belonging to the Low-declining trajectory (fully adjusted RRR = 1.035, 95% CI: 1.012-1.058, P = 0.003). This association was more pronounced among participants with primary school education or below (RRR = 1.07, 95% CI: 1.04-1.11) and rural residents (RRR = 1.05, 95% CI: 1.03-1.08), with significant effect modification by education (P for interaction = 0.031) and residence (P for interaction = 0.024). Cold spell days showed no significant association (RRR = 1.02, 95% CI: 0.96-1.08, P = 0.554). Sensitivity analyses supported result robustness.

CONCLUSIONS

Cumulative heatwave exposure is associated with an increased risk of belonging to the most vulnerable IC trajectory among Chinese middle-aged and older adults, particularly among socioeconomically disadvantaged groups. These findings underscore the urgent need for targeted climate adaptation strategies to protect functional health in aging populations.