Green Space, Mental Health, Physical Activity and Body Mass Index in a Cohort of Women Up to 15 Years Postpartum: A Multilevel Longitudinal Study

Abstract

Background: Most epidemiological studies of green space and health use cross-sectional data, focus on green space quantity and pay little attention to sensitive periods in the lifecourse. Objective: To examine trajectories in mental health, moderate to vigorous physical activity lasting at least 30 minutes (MVPA) and body mass index (BMI) in association with measures of green space quantity and quality among women in the postpartum period. Methods: 3574 women who did not change neighbourhood were observed up to 6 occasions each over 12 years from 2004 onwards (20,084 observations). Multilevel growth curve models were used to examine the patterning of the Kessler 6 psychological distress scale, MVPA, and BMI. Green space quantity was measured by percentage land-use. Green space quality was self-reported. Models were adjusted for Indigenous status, qualifications, employment, area disadvantage and remoteness. Results: Green space quantity was associated with lower BMI (e.g. 21-40% coefficient: -0.73kg/m2 (95%CI -1.39 to –0.08). This association between green space quantity and BMI strengthened as women aged. BMI was not associated with green space quality. However, women who lived near good quality green space reported better mental health consistently over time (rate ratio 0.89, 95%CI 0.85 to 0.93) and also participated in MVPA more often (rate ratio 1.04, 95%CI 1.01 to 1.07). A two-way interaction suggested quality green space supports the maintenance of MVPA over time. Conclusions: Green space quantity and quality matter for different health outcomes in the postpartum period. Quality green space may help prevent a decline in MVPA as women age.