Objectives: Indoor air pollution exposure is harmful to people’s physical and mental health, especially in the elderly population, and represents a major issue for human health. Natural ventilation can improve indoor air quality and remove indoor contamination, thus reducing the adverse effects of indoor air pollution exposure on physical and mental health. Depressive symptoms are the most common mental health issue among elderly individuals. However, evidence linking the frequency of indoor natural ventilation to depressive symptoms in the elderly population is limited.

Methods: This study included 7887 individuals 65 years and older from 2017 to 2018 in the China Longitudinal Healthy Longevity Survey (CLHLS). The frequency of indoor natural ventilation was measured as the self-reported frequency of window opening per week in each season. Depressive symptoms were measured by the 10-item Center for Epidemiologic Studies Short Depression Scale (CES-D). Using a model adjusted for demographic, socio- economic, health status, and environmental factors, the correlation between indoor ventilation frequency and depressive symptoms was verified through logistic regression.

Results: Among the 7887 elderly people included in this study, 1952 (24.7%) had symptoms of depression. In the fully adjusted model, compared with the lower indoor overall ventilation frequency group (indoor ventilation frequency: 0–3 times/week), the higher indoor overall ventilation frequency group (indoor ventilation frequency: 6–8 times/week) showed a decrease in depressive symptoms by 33 % [OR: 0.67, 95 % (CI): 0.51–0.88]. Subgroup analysis and sensitivity analysis yielded similar results.

Conclusions: High frequency of indoor ventilation is significantly associated with the reduction of depressive symptoms in Chinese individuals 65 years old or older. This result provides strong evidence for health intervention and policy formulation. Encouraging an increase in indoor ventilation frequency will be an economically beneficial measure to promote healthy aging of the Chinese population.