Association of vitamin D and green space. Results from the GINIplus & LISA birth cohorts

Background and Aim While there is increased awareness and a growing body of evidence for beneficial health effects of green space surrounding the home, underlying mechanisms are not yet fully understood. Here, we investigate vitamin D as a potential pathway linking greenness and health, including cardiometabolic, respiratory and mental health. Methods 25-hydroxyvitamin D (25(OH)D) was measured at ages 10 and 15 years in the German birth cohort studies GINIplus and LISA. Greenness was measured using the Landsat-derived Normalized Difference Vegetation Index (NDVI) in a 500m buffer surrounding the home. We applied linear and logistic regression models at both time points adjusted for month of examination, sex, study area, study, parental education and BMI (N_10Y=2504, N_15Y=2613). In additional analyses, physical activity, time spent outdoors, urbanicity, and vitamin D-related genes were investigated as potential effect modifiers. Results A 2-standard-deviation (SD) increase in NDVI was significantly associated with increased 25(OH)D values at ages 10 and 15 years (β_10y=2.41nmol/l, p=<0.01; β_15y =2.03nmol/l, p=0.02. In stratified analyses, the association was strongly attenuated in participants spending more than 5h/day outside in summer (β_10y=-2.39nmol/l, p=0.165; β_15y =-1.07nmol/l, p=0.675), having a high physical activity level (β_10y=0.62nmol/l, p=0.637; β_15y =1.71nmol/l, p=0.296), taking supplements (β_10y=-2.05nmol/l, p=0.386; β_15y =0.10nmol/l, p=0.296), or examined during winter season (β_10y=0.86nmol/l, p=0.352; β_15y =0.07nmol/l, p=0.970). In a subset with genetic data, a significant gene-environment interaction of NDVI with CYP2R1, an upstream gene in 25(OH)D synthesis, was observed. Conclusions We observed robust associations between greenness measured by NDVI and 25(OH)D levels in children and adolescents independent of other confounders and additionally supported by the presence of a gene-environment interaction. Effects were stronger in those having lower vitamin D levels due to genetically reduced 25(OH)D synthesis or due to their covariate profile. Keywords Vitamin D, Greenspace, Children, Epidemiology