Biological age acceleration mediates effects of household air pollution from solid fuels on dementia risk: A prospective cohort study in China

Population aging exacerbates the health threat stemming from inequalities in access to cleaner fuels, yet household air pollution (HAP) from the use of polluting fuels and its association with biological aging and subsequent dementia risk remain underexplored. We aimed to explore potential pathways linking household fuel use to aging and incident dementia, via a cohort study of 8,561 Chinese adults aged 45-80. The household fuel use trajectories during the baseline period (2011-2015) were investigated, and biological age was assessed in 2015 using the Klemera Doubal method along with 11 clinical biomarkers. Dementia cases were documented during the follow-up period (2015-2020). Cox proportional hazards models were employed to estimate the association between household fuel use and dementia risk, while assessing the mediation effects of biological age acceleration. Additionally, potential benefits of leisure engagement were examined. A total of 580 (6.8 %) participants developed incident dementia. Compared to consistent use of cleaner fuels, consistent solid fuel use and switching from cleaner to solid fuels were significantly associated with an acceleration of 0.14 (95 % CI: 0.08, 0.19) and 0.15 (95 % CI: 0.05, 0.24) years of biological age, respectively; consistent use of solid fuels was significantly associated with an evaluated risk of dementia (HR = 1.32, 95 % CI: 1.06, 1.64). Accelerated biological age (as a continuous variable) and being biologically older (as a binary variable) partially mediated 6.7 % and 5.3 % of dementia risk associated with consistent solid fuel use. Moreover, leisure engagement was independently associated with an attenuation of 0.13 (95 % CI: 0.08, 0.19) years of biological age, with little evidence of interaction with household fuel use on either additive or multiplicative scales. Accelerated biological age may be an intermediate factor in dementia pathogenesis linked to household solid fuel combustion. Our findings emphasize that expanding access to cleaner fuels might contribute to relieving both biological aging and dementia burden.