Environmental exposures and mental health: longitudinal results from the German National Cohort (NAKO).

Background

Environmental exposures such as air pollution, population density, and climate-related stressors may influence mental health, yet large-scale longitudinal evidence is limited. This study examined associations of environmental exposures with depressive and anxiety symptoms, and stress in the German National Cohort (NAKO).

Methods

We analyzed data of over 70,000 adults aged 19-74 years from the NAKO baseline (2014-2019), with repeated survey assessments in 2020 and 2022 of depressive symptoms (Patient Health Questionnaire-9), anxiety symptoms (Generalized Anxiety Disorder 7-item), and stress (Patient Health Questionnaire-stress) scores. The annual mean of environmental exposures, including nitrogen dioxide (NO2), particulate matter (PM), black carbon, air temperature, precipitation, relative humidity, greenness (Normalized Difference Vegetation Index), and indicators of the built and social environment were assessed at the participants' residences at baseline and standardized with their interquartile range (IQR). Longitudinal associations of exposures with mental health outcomes were assessed using covariate-adjusted linear mixed models. Subgroup analyses were conducted stratifying by urbanization level, obesity, lung disease, and cardiovascular disease status.

Findings

Higher mean air temperature (per IQR) was associated with higher depressive symptom scores (β = 0.07, 95% CI: 0.03-0.12), anxiety symptom scores (β = 0.05, 95% CI: 0.01-0.09), and stress scores (β = 0.05, 95% CI: 0.01-0.09). Exposure to NO2 was associated with higher depressive symptom scores (β = 0.08, 95% CI: 0.03-0.14). A higher population density within 100 m was associated with higher depressive, anxiety symptoms, and stress scores. In contrast, higher levels of greenness, precipitation, and relative humidity were associated with lower depressive symptom scores. Most of the associations with depressive or anxiety symptom scores were stronger in females, younger adults, people with obesity and those living in cities.

Interpretation

Improving air quality, enhancing urban green spaces, and implementing climate-adaptation strategies could help promote mental well-being, particularly in urban and vulnerable populations.