Association of residential greenness and sleep duration in adults: A prospective cohort study in China.

BACKGROUND

Exposure to residential greenness has been linked with improved sleep duration; however, longitudinal evidence is limited, and the potential mediating effect of ambient fine particulate matter (PM) has yet to be assessed.

METHODS

We obtained data for 19,567 participants across seven counties in a prospective cohort in Ningbo, China. Greenness was estimated using Normalized Difference Vegetation Index (NDVI) within 250-m, 500-m and 1000-m buffer zones, while yearly average PM concentrations were measured using validated land-use regression models, both based on individual residential addresses. Sleep duration was assessed using structured questionnaires at baseline and during follow-up. The longitudinal associations between residential greenness and sleep duration were evaluated using linear mixed-effect models. Adjustments for PM and county were implemented. To identify the effect of greenness exposure on age-related declines in sleep duration, we included an interaction term between NDVI and visit (baseline and follow-up). Additionally, half-longitudinal mediation analyses were conducted to evaluate the potential mediating role of PM in this relationship.

RESULTS

Each interquartile range (IQR) increase in NDVI within 250 m, 500 m and 1000 m was associated with increases in sleep duration of 0.044 h (95% CI: 0.028,0.061), 0.045 h (95% CI: 0.028,0.062), and 0.031 h (95% CI: 0.013,0.049), respectively. Associations were attenuated after adjusting for PM. Farmers, homemakers, and short-nap individuals benefited the most from greenness exposure. Higher greenness exposure significantly lowered PM levels, which was associated with a slower decline in sleep duration over the follow-up period.

CONCLUSION

Exposure to higher levels of residential greenness was associated with increased sleep duration and a slower decline in sleep over time. County-level heterogeneity in the effects of residential greenness on sleep duration was observed. PM partially mediating this relationship.