Assessing the Effect of Ultraviolet Radiation, Residential Greenness and Air Pollution on Vitamin D Levels: A Cohort Study in China

Abstract

BACKGROUND AND AIM: Vitamin D is obtained in the diet or from exposure to ultraviolet rays, and thus can be modified by environment factors. We aim to assess individual and combined effects of ultraviolet (UV) radiation, residential greenness, and air fine particulate matter (PM2.5) with vitamin D levels in a community-based cohort study of elderly aged over 65 years old in China. METHODS: We used the 2012-2014 Chinese Longitudinal Healthy Longevity Survey data for analysis, obtained daily UV radiation from the closest monitoring station and measured residential greenness through satellite-derived Normalized Difference Vegetation Index (NDVI) in a 500 m radius around address. Annual PM2.5 was calculated using satellite-based data (0.1 degrees × 0.1 degrees). Vitamin D levels were defined according to serum 25-hydroxyvitamin D: non-deficiency (≥50 nmol/L) and deficiency (50 nmol/L). We used the generalized estimating equation for longitudinal analysis, adjusting sociodemographic information, eating habits, lifestyle, and season of blood draw. RESULTS:We included 1336 participants, with a mean age of 83 at baseline. In single exposure models, UV radiation and greenness were positively associated with vitamin D non-deficiency, while PM2.5 was inversely associated with it. In the saturated model with three-exposures, each 0.1-MJ/(m2·d) increase in annual UV radiation was associated with a 86% higher odds of vitamin D non-deficiency [odds ratio (OR) 95% CI: 1.50, 2.30], each 0.1-unit increase in annual NDVI was 22% higher odds of vitamin D non-deficiency (OR 95% CI: 1.10, 1.36), while each 10-μg/m3 increase annual PM2.5 was associated a 20% lower odds of vitamin D non-deficiency (OR 95% CI: 0.74,0.85). In our stratified analysis assessing effect modification, the association of UV and vitamin D non-deficiency was strongest in the lowest PM2.5 area and highest greenness area. CONCLUSIONS:UV radiation, residential greenness, and PM2.5 are associated with vitamin D deficiency, and can influence aging pathways and elderly health. KEYWORDS: Air pollution, Green Space, Environmental epidemiology