Biostatistics

Background

Little research exists regarding the relationships between green space and postpartum depression (PPD). Existing studies investigated only antenatal depression and solely relied on satellite-based green space data, without considering green space types and the mediating role of physical activity (PA).

Methods

Clinical data were obtained from electronic health records of 415,020 singleton births at the Kaiser Permanente Southern California in 2008-2018. PPD ascertainment was based on both diagnostic codes and prescription medications. Maternal exposures near the residential addresses at delivery were assessed using street view-based green space and vegetation type (i.e., street tree, low-lying vegetation, and grass), satellite-based measures [i.e., Normalized Difference Vegetation Index (NDVI), land-cover green space, and tree canopy cover], and proximity to the nearest park. Multilevel logistic regression was applied to estimate the association between green space and PPD. A causal mediation analysis was performed to estimate the proportion mediated by PA during pregnancy in the total effects of green space on PPD.

Findings

A reduced risk for PPD was associated with total green space exposure based on street-view measure [500m buffer, adjusted odds ratio (OR) per interquartile range: 0.980, 95% CI: 0.966–0.994], but not NDVI, land-cover greenness, or proximity to a park. Compared to other types of green space, tree coverage showed stronger protective effects. The proportions of mediation effects attributable to PA during pregnancy ranged from 2.5% to 7.2% across green space indicators.

Interpretation

Street view-based green space and tree coverage were associated with a decreased risk of PPD. The observed association was primarily due to increased tree coverage, rather than low-lying vegetation or grass. Increased PA was a plausible pathway linking green space to lower risk for PPD.

Funding Information

This study was supported by the National Institute of Environmental Health Sciences (NIEHS; R01ES030353).

Declaration of Interests

None.

Ethics Approval Statement

This study was approved by the Institutional Review Board of KPSC and the University of California, Irvine.