Investigating biological sex as a moderator of the association of nature exposure with brain health: a cross-sectional UK biobank analysis

In this cross-sectional analysis of the UK Biobank, we investigated whether biological sex moderates the association of residential nature exposure with brain volume or cognitive function. We included 11,448 cognitively healthy UK residents aged 37–73 years (98% White; 51% female). Residential nature exposure was estimated as the percentage of land classified as natural environment within 1000 m and 300 m buffers around each participant’s home. Structural brain magnetic resonance imaging (MRI) outcomes included total grey matter volume, total white matter volume, and average hippocampal volume, all normalized for head size. Cognitive function was assessed with the Trail Making Test (B-A) and the Symbol Digit Substitution Test. In linear regression models, higher residential nature exposure at both buffer sizes was associated with greater grey matter volume (1000 m: β = 629 mm³ per 10% increment in nature exposure; 95% CI: 234 to 1023; p = 0.002; 300 m: β = 642 mm³; 95% CI: 286 to 997; p < 0.001), greater white matter volume (1000 m: 659 mm³; 95% CI: 229 to 1089; p = 0.003; 300 m: β = 527 mm³; 95% CI: 140 to 914; p = 0.008), and more correct matches on the Symbol Digit Substitution Test (1000 m: β = 0.106 matches; 95% CI: 0.057 to 0.154; p < 0.001; 300 m: β = 0.049 matches; 95% CI: 0.006 to 0.092; p = 0.03). In males, compared with females, higher nature exposure was associated with a greater increment in grey matter volume (1000 m; β = 635 mm³; 95% CI: 53 to 1217; p = 0.03; 300 m: β = 634 mm³; 95% CI: 102 to 1167; p = 0.02), and with a greater reduction in Trail-Making Test B-A time (300 m only: β = 0.284 s; 95% CI: 0.016 to 0.551; p = 0.04). These sex differences showed some sensitivity to participant residence changes and to type of nature exposure measure. Residential nature exposure may support brain volume and cognitive function, and some of the potential benefits may vary by sex.