Sun Exposure Behaviour and Vitamin D in South Asian Compared with White Caucasian Adolescents: Prospective Cohort Study

Background: Sun exposure guidance advises minimisation to reduce skin cancer risk, but advice is geared for white-skinned people. Melanin reduces skin synthesis of vitamin D from solar ultraviolet radiation (UVR), and adolescence is a key life-stage for bone mass acquisition. Methods: This prospective cohort study investigated year-round vitamin D status and its determinants in 143 South Asian adolescents (12–15 y; brown skin) living in Greater Manchester, UK. Serum 25OHD, personal UVR doses, time outdoors, and photoprotective measures were assessed across four seasons, and the findings were compared with those of 131 white Caucasian adolescents studied using identical protocols. Results: Severe vitamin D deficiency (25OHD < 25 nmol/L) was prevalent in South Asians, affecting 79% of girls and 69% of boys in winter, persisting year-round in 59% of girls and 23% of boys, and accompanied by winter PTH levels > the upper reference range in 59% of boys and 45% of girls. Personal UVR doses and time outdoors were lower on summer weekend days (boys 53 min, girls 60 min) vs. schooldays (boys 105 min, girls 108 min) in South Asians (p < 0.01). The findings contrasted with those in white Caucasians, where time outdoors was similar on summer weekend days and schooldays (weekend days: boys 131 min, girls 101 min, p < 0.01 vs. South Asians). Only 26% of South Asians vs. 86% of white Caucasians took a holiday abroad during the year, and days abroad significantly contributed to vitamin D status. Both groups had low oral vitamin D intake. Conclusions: Raising vitamin D status is crucial to prevent secondary hyperparathyroidism in South Asian adolescents and skin type-related sun exposure guidance is required.