Zhong Nan Da Xue Xue Bao Yi Xue Ban. 2026 Jul 28;51(7):1411-1425. doi: 10.11817/j.issn.1672-7347.2026.260128.
ABSTRACT
OBJECTIVES: Stroke is one of the leading causes of death and disability in China and imposes a substantial disease burden. Population aging has further increased the challenges of stroke prevention and control among middle-aged and older adults. Although environmental relative humidity (RH) is considered an important environmental determinant of health, existing evidence regarding its association with stroke remains inconsistent, with prospective evidence from Chinese populations being particularly limited. This study aims to investigate the association between environmental RH and the risk of incident stroke among middle-aged and older adults in China and to assess the mediating role of frailty and potential gender differences in this association.
METHODS: A dynamic-entry cohort was constructed using data from the 2011, 2013, 2015, and 2018 waves of the China Health and Retirement Longitudinal Study (CHARLS), with a total of 19 582 participants ultimately included. Participants were followed from the date of the first interview at which they met the eligibility criteria until the first report of incident stroke, loss to follow-up, or the end of follow-up in 2020. Hourly RH at each participant's place of residence was obtained from ERA5 reanalysis dataset, and the mean RH during the year preceding enrollment was calculated. Participants were categorized into low-, moderate-, and high-humidity groups according to tertiles, with the low-humidity group serving as the reference. Incident stroke was defined as the first self-reported physician diagnosis of stroke during follow-up. Cox proportional hazards models were used to estimate HR and 95% CI, with sequential adjustment for sociodemographic characteristics, health behaviors, mean temperature during the year preceding enrollment, and other potential confounders. Gender-stratified analyses were also performed. Counterfactual-based mediation analysis was conducted to assess the mediating effect of the frailty index (FI), and nonparametric bootstrap resampling with 5 000 repetitions was used to estimate the proportion mediated by FI and its uncertainty.
RESULTS: During a median follow-up of 7 years, 1 235 participants (6.31%) developed incident stroke. Cox regression analyses showed that, compared with the low-humidity group, both the moderate- and high-humidity groups had increased risks of incident stroke. In the fully adjusted model, the HR was 1.119 (95% CI 1.033 to 1.213) for the moderate-humidity group and 1.279 (95% CI 1.227 to 1.331) for the high-humidity group (both P<0.01), with effect estimates progressively attenuated as the degree of model adjustment increased. Gender-stratified analyses showed that the association was more pronounced in men. In the fully adjusted model, the HRs among men were 1.145 (95% CI 1.031 to 1.272) for the moderate-humidity group and 1.352 (95% CI 1.268 to 1.442) for the high-humidity group. Among women, the risk was also elevated in the high-humidity group (HR=1.186, 95% CI 1.092 to 1.288), whereas the association for the moderate-humidity group was attenuated and not statistically significant (HR=1.082, 95% CI 0.954 to 1.227). Mediation analysis indicated that the total effect of environmental RH on incident stroke risk was statistically significant (P<0.01). RH was associated with frailty level (β=0.22, P<0.01), and frailty mediated 22.0% of the association between RH and incident stroke risk.
CONCLUSIONS: Higher environmental RH is associated with an increased risk of incident stroke among middle-aged and older adults in China, and this association may be partially mediated through frailty. Gender differences were observed, with the association being more pronounced in men. These findings suggest that exposure to high-humidity environments should be considered in primary stroke prevention and healthy aging management, with enhanced risk identification and health guidance for potentially high-risk subgroups, particularly individuals with frailty and men.
PMID:42763297 | DOI:10.11817/j.issn.1672-7347.2026.260128