Household solid fuel use increases frailty risk in Chinese middle-aged and older adults: a prospective cohort study

With the aggravation of population aging, frailty has become a major public health issue. However, the association between indoor air pollution from solid fuels and frailty is unclear. We analyzed data collected from 13,233 middle-aged and older adults (> 45 years) who were non-frail at baseline survey (2011, 2013, 2015, and 2018) from the China Health and Retirement Longitudinal Study to investigate the association between the use of solid fuels for cooking and frailty. After excluding 1853 participants with missing data on heating fuel, 11,380 individuals surveyed in 2011, 2013, and 2015 were retained for the heating-fuel analyses. We constructed the frailty index (FI) based on 40 health deficit items. Frailty was defined as FI > 0.25. The seven fuel types surveyed were categorized as clean and solid fuels. Time-dependent Cox proportional hazards models were used to analyze the association of solid fuel use for cooking or heating, alone or in combination, with frailty. Cox models were also used to explore the association of fuel type switching. Covariates included individual characteristics, health behaviors, socioeconomic factors, and household dwelling characteristics. Sensitivity analyses were performed to test the robustness of the main results, and interaction and subgroup analyses were performed to explore the influence of potential confounding factors on the results. Compared with participants using clean fuels, those using solid fuels had a higher risk of frailty (cooking: HR 1.46, 95% CI 1.28-1.67, p < 0.001; heating: HR 1.58, 95% CI 1.29-1.94, p < 0.001). Participants who switched from solid to clean fuel showed a reduction in the risk of frailty (HR 0.61, 95% CI 0.51-0.73, p < 0.001). Indoor air pollution caused by solid fuels is associated with an increased risk of frailty among middle-aged and older adults in China. Our findings provide evidence supporting the restriction of solid fuel use and improvement of indoor air quality to protect this population from frailty risk.