Green and blue spaces, COVID-19 lockdowns, and mental health: An Australian population-based longitudinal analysis

Australia experienced some of the world's longest and most stringent lockdowns during the COVID-19 pandemic. While lockdown measures had consequences for mental health, investigation is lacking on the potential for green and blue space coverage within people's local environments to ameliorate the impact of lockdowns with varied lengths using longitudinal cohorts. This study examined the impact of lockdown durations on population mental health and tests the effect modification of neighbourhood green and inland and coastal blue space coverage in metropolitan areas. We merged population-based longitudinal data on more than 11,000 individuals collected over a ten-year period from 2012 to 2021 with national land use data describing green and blue space coverage. We used fixed effect models to estimate the relationship between lockdowns (with different durations and staggered introduction) and mental health, controlling for sociodemographic, health, and geographical confounders, and tested the significance of effect modification of green and blue space. Results show that extended lockdowns led to considerably larger decreases in mental health (COVID-y1: -2.66, 95%CI: -3.43, -1.89; COVID-y2: -2.65, 95%CI: -3.33, -1.97) relative to short lockdowns. The mental health effect of lockdowns was smaller where green spaces and inland and coastal blue spaces were available. Effect modification was statistically significant for green space, with smaller negative mental health effects observed where there was sizeable green space coverage, particularly during long lockdowns (COVID-y1: -2.69, 95%CI: -3.63, -1.76 for coverage <5%; -3.27, 95%CI: -4.70, -1.84 for coverage 5%-10%; -0.60, 95%CI: -2.03, 0.83 for coverage ≥30%; COVID-y2: -2.74, 95%CI: -3.62, -1.87 for coverage <5%, -2.95, 95%CI: -3.98, -1.92 for coverage 5%-10%; -2.08, 95%CI: -3.28, -0.88 for coverage ≥30%). Findings support the consideration of nature exposure to improve people's mental wellbeing and resilience when designing lockdown measures in response to future public health emergencies.