Hidden vitamin D insufficiency in a sun-rich equatorial country: age-, sex-, and season-specific evidence from 2961 Somali children

Abstract

This study aimed to determine the prevalence of vitamin D deficiency and insufficiency, and to evaluate age-, sex-, and season-specific variations in serum 25(OH)D levels among Somali children and adolescents. This retrospective cross-sectional study included pediatric outpatients aged 0-18 years who attended a tertiary care hospital in Mogadishu, Somalia, between January 2020 and August 2025. Serum 25(OH)D levels were analyzed in 2961 participants and categorized as deficient (<12 ng/ml), insufficient (12-20 ng/ml), or sufficient (>20 ng/ml) according to Global Consensus Recommendations. Participants were stratified by age group, sex, and season. Statistical analyses were performed using non-parametric tests, with P < .05 considered statistically significant. Mean serum 25(OH)D levels decreased progressively with age, with the highest concentrations observed in infants aged 0-1 year (53.8 ± 18.1 ng/ml) and the lowest in adolescents aged 12-18 years (27.4 ± 13.1 ng/ml). Vitamin D deficiency was absent in infants and rare in children aged 1-6 years, but increased substantially in older age groups, reaching 9.4% deficiency and 23.7% insufficiency among adolescents. Males consistently exhibited higher serum 25(OH)D levels than females across all age groups and seasons (P < .001). Seasonal variation was observed, with the lowest mean levels recorded during July-September. Despite abundant year-round sunlight, vitamin D insufficiency and deficiency are prevalent among Somali children, particularly in adolescents and females. These findings highlight the need for age- and sex-specific public health strategies, including targeted screening and supplementation beyond early childhood, to improve 25(OH)D status in pediatric populations living in sun-rich environments.