Exploring the pathways between green space and blue space, and cognitive function in later life: a mediation analysis...

The pathways by which green space and blue space exposure influence cognitive function are unclear.

To investigate the association between green space and blue space exposure and cognitive function and potential mediating pathways through which this association may act, we used multilevel structural equation models and longitudinal data from Waves 1 and 2 of the Northern Ireland Cohort for the Longitudinal Study of Ageing study. Cognitive function was assessed by the Mini-Mental State Examination (MMSE). We assessed green space and blue space exposure using: (1) NDVI and NDWI (Normalised Difference Vegetation/Water Index); (2) accessibility of green space and blue space (distance to the nearest parks/coastlines); and (3) availability of green space and blue space (the proportion of vegetation/water bodies). Potential mediators included: (2) moderate-to-vigorous physical activity (MVPA); (2) walking; (3) social contact; (4) social support and (5) fine particulate matter with a diameter of 2.5 µm or less.

First, MVPA mediates the association between NDVI (Coef.=0.0017; SE=0.0008), NDWI (0.0035; SE=0.0015), accessibility of green space (Coef.=-0.0015; SE=0.0007) and MMSE scores. Second, social contact also mediates the association between availability of green space (Coef.=0.0023; SE=0.0009), accessibility of blue space (Coef.=-0.0009; SE=0.0004) and MMSE scores.

Our findings suggested that green space and blue space exposure are important predictors of cognitive function in later life and that they may exert their effect via multiple pathways. Green space and blue space exposure may contribute to healthy ageing.