Associations between natural area availability and morbidity: a cross-sectional study using health insurance billing data from Germany

Objectives Access to nature has been associated with improved physical and mental health through multiple pathways, including stress reduction, physical activity promotion and reduced chronic disease risks. In contrast, urban areas lacking nature often expose residents to pollution, noise and heat. This study examines whether natural area availability is associated with morbidity. Design We conducted a cross-sectional study using 2023 outpatient billing data, with the Charlson Comorbidity Index (CCI) as a measure of morbidity. (Mixed) linear regression models were applied in ecological-regional (full sample) and individual (2.5% stratified random sample) designs to examine associations between CCI and three natural area indicators (semi-natural, forest and water) while controlling for sociodemographic, socioeconomic and infrastructural variables. Setting Nationwide ambulatory claims data (secondary data analysis). Participants Data from 72.7 million individuals with statutory health insurance in Germany were used. Results In the ecological-regional analysis, higher proportions of semi-natural, forest and water areas per inhabitant were negatively associated with the average regional CCI, with coefficients of −0.433 (95% CI −0.723 to −0.143, p=0.004), −0.080 (95% CI −0.139 to −0.021, p=0.008) and −0.612 (95% CI −1.137 to −0.087, p=0.022). Multilevel analyses confirmed these associations at the individual level: an increase of one SD of semi-natural (−0.013, 95% CI −0.023 to −0.003, p=0.009), forest (−0.012, 95% CI −0.022 to −0.002, p=0.024) or water area (−0.011, 95% CI −0.021 to −0.001, p=0.032) was each associated with a lower CCI. Conclusion Regions with more natural areas were associated with lower morbidity. Green spaces may support better health. Equitable access to natural environments could promote population health.