The role of greenspace in vitamin D status: cross-sectional, observational evidence from the UK Biobank.

Background: Exposure to greenspace is associated with positive health outcomes. This relationship is poorly understood, with limited knowledge on the mechanisms through which greenspace affects health, including biomarkers of greenspace effects.

Methods: We used data from the UK Biobank to examine the cross-sectional association between greenspace exposure and serum 25-hydroxyvitamin D [25(OH)D]. Greenspace was assessed in a 300- and 1000-m buffer of land cover around each participant's home location, while 25(OH)D was measured by chemiluminescent immunoassay. We used multinomial regression models accounting for individual and area-level covariates. Additionally, we conducted mediation analysis by physical activity and time spent outdoors and performed various stratifications and sensitivity analyses.

Results: A total of 443 810 participants (mean age: 56.51 [SD: 8.1] years, 53.6% females) were included in the study. Compared to the first quartile (within 1000 m buffer of participants' home locations), we found positive associations between the highest quartile of greenspace and insufficient (OR: 1.16, 95% CI: 1.11, 1.21) and sufficient 25(OH)D (OR: 1.36, 95% CI: 1.30, 1.42) categories after adjusting for individual- and areal-level covariates. Other quartiles showed similar but smaller effect estimates. The observed association exhibited similar directionality when a 300 m buffer was used, and was more pronounced among males, and most deprived individuals. Physical activity and time spent outdoors partially explained the relationship between greenspace quartiles and sufficient serum 25(OH)D.

Conclusion: We found positive associations between greenspace quartiles and serum 25(OH)D categories. This has implications for greening policies aimed at reducing vitamin D deficiency through controlled sun exposure.