Relationship Between Sunlight Exposure, Erythemal Dose, and Vitamin D Concentrations in Adolescents: A Cross-Sectional, Multi-center Study.

Background Vitamin D (Vit. D) plays a vital role in bone health and calcium-phosphorus homeostasis. Its deficiency is a major global health concern, affecting populations even in sun-rich countries like India. Indian adolescents, predominantly urban dwellers and girls, show a higher deficiency of Vit. D. Objective assessment of sunlight exposure in the Indian pediatric population in relation to Vit. D status is limited. Objectives This study examined the association between Vit. D concentrations, sunlight exposure (as measured using Polysulphone (PSU) dosimeter badges), and anthropometric parameters among urban and rural Indian adolescents across six states. The study investigated the differences in Vit. D status with changes in seasons, sex, and geographical regions. Methods A large-scale, multi-center research project that included 2500 children and their reported Vit. D prevalence was conducted from July 2016 to October 2017. This cross-sectional study was conducted in six Indian states across urban and rural settings. The study took place during the winter and rainy seasons. Vit. D status was determined using a previously standardized liquid chromatography-mass spectrometry (LC-MS)/MS-based method to measure 25-hydroxy-vitamin D3 (25(OH)D3) from dried blood spots, as 25(OH)D accounts for over 90% of the total 25(OH)D3 concentration in Indians. In the current study, we report data on a subset of 545 children who wore PSU badges on their wrists. Anthropometric data - height, weight, and BMI - were collected following standard protocols. Vit. D concentrations were measured from dried blood spots. Sunlight exposure was quantified as standard erythemal dose (ED) using PSU badges. Statistical analyses of the data included correlation, Mann-Whitney U tests, and multiple regression. Results Urban children were taller, heavier, and had lower Vit. D concentrations, sunlight exposure, and ED than rural children (p < 0.05). Rural boys had the highest Vit. D concentrations (24.6 ng/ml). Vit. D had a significant negative correlation with weight in urban girls (p < 0.05). Significant negative correlation (p < 0.05) was found between BMI, waist circumference, and Vit. D concentrations, and a positive association was found between ED and Vit. D concentrations in urban areas. There was a strong positive correlation between ED, sunlight exposure, and Vit. D concentrations (p>0.05). The winter season and rural settings saw notably higher ED as compared to the rainy season and the urban setting. Conclusion Sunlight exposure was a significant predictor of Vit. D status in Indian adolescents. Rural residence and winter season were associated with higher sunlight exposure and better Vit. D status. Girls were particularly vulnerable to Vit. D deficiency. These findings highlight the need for targeted interventions, especially in urban areas and among girls, to improve sunlight exposure and Vit. D status. Policy efforts should consider promotion of outdoor activity, with particular emphasis on improving Vit. D status during the monsoon season.