Heatwave Days Linked to Declining Intrinsic Capacity in Chinese Middle-Aged and Older Adults

Cumulative exposure to heatwaves is associated with an increased risk of following the most vulnerable trajectory of intrinsic capacity among middle-aged and older adults in China, according to a study published in BMC Public Health that analyzed data from the China Health and Retirement Longitudinal Study (CHARLS). Intrinsic capacity, a multidimensional construct proposed by the World Health Organization as a core indicator of healthy aging, spans five domains: locomotion, sensory function, vitality, psychological well-being, and cognition.

The researchers drew on 1,393 participants aged 45 to 80 years who had complete intrinsic capacity assessments across three waves of CHARLS, in 2011, 2013, and 2015. Intrinsic capacity was operationalized as a composite score ranging from 0 to 10 across the five domains. K-means clustering was used to identify heterogeneous trajectories of capacity over time, and extreme temperature events were defined using city-specific daily apparent temperature, with a heatwave defined as temperature at or above the 95th percentile for at least three days and a cold spell as temperature at or below the 5th percentile for at least three days.

Three distinct trajectories emerged from the clustering analysis: a high-stable group comprising 41.3 percent of participants, a moderate-declining group comprising 26.4 percent, and a low-declining group comprising 32.3 percent. Using multinomial logistic regression with progressive adjustment for sociodemographic, lifestyle, and health-related covariates, the team examined whether cumulative heatwave days between 2011 and 2015 were associated with membership in these trajectory groups.

Each additional heatwave day significantly increased the risk of belonging to the low-declining trajectory, with a fully adjusted relative risk ratio of 1.035 (95 percent confidence interval: 1.012 to 1.058; P = 0.003). The association was more pronounced among participants with primary school education or below, who had a relative risk ratio of 1.07 (95 percent confidence interval: 1.04 to 1.11), and among rural residents, who had a relative risk ratio of 1.05 (95 percent confidence interval: 1.03 to 1.08). Significant effect modification was observed for both education (P for interaction = 0.031) and residence (P for interaction = 0.024), indicating that the association differed across these socioeconomic subgroups.

In contrast, cold spell days showed no significant association with trajectory membership, with a relative risk ratio of 1.02 (95 percent confidence interval: 0.96 to 1.08; P = 0.554). The authors report that sensitivity analyses supported the robustness of the results.

The study is observational in design, and its findings describe associations between cumulative heatwave exposure and trajectory membership rather than established causal effects. The analysis was limited to participants with complete intrinsic capacity assessments across the three CHARLS waves, and the exposure window covered the 2011 to 2015 period in China. The authors note that global climate change has increased the frequency, intensity, and duration of extreme temperature events while population aging poses growing public health challenges, and that the association between extreme temperature events and longitudinal intrinsic capacity trajectories had remained unknown prior to this work.

The authors conclude that cumulative heatwave exposure is associated with an increased risk of belonging to the most vulnerable intrinsic capacity trajectory among Chinese middle-aged and older adults, particularly among socioeconomically disadvantaged groups, and that these findings underscore the need for targeted climate adaptation strategies to protect functional health in aging populations.

Subject of Research: The association between extreme temperature events and intrinsic capacity trajectories among middle-aged and older adults in China

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

Article References: Huang, L., Huang, Y., Qian, B., Zhou, C., Huang, Y., Wang, Y., Sun, Y., Huang, X., Yao, W., Chen, Y., Wang, Y., & Luo, Z. (2026). Association between extreme temperature events and intrinsic capacity trajectories among middle-aged and older adults: the China Health and Retirement Longitudinal Study (CHARLS). BMC Public Health, 26(1), Article 2736. https://doi.org/10.1186/s12889-026-29470-y

Image Credits: AI Generated

DOI: 10.1186/s12889-026-29470-y

Keywords: heatwaves, intrinsic capacity, healthy aging, CHARLS, cold spells, older adults, China, climate change, longitudinal study, health inequalities, public health, Association