Prevalence of Vitamin D Deficiency according to Climate Conditions among a Nationally Representative Sample of Iranian Adolescents: the CASPIAN-III Study

Background: Sunlight is the main source of vitamin D; therefore, environmental factors might have an important role in the high prevalence of hypovitaminosis D in children. This study aimed to assess the vitamin D status according to the climate of the living area in a nationally representative sample of Iranian adolescents. Material and Methods: This nationwide cross-sectional survey was performed among a representative sample of 1,095adolescents aged 10-18 years, selected by multistage cluster sampling method from 27 provinces of Iran. Serum 25-hydroxyvitamin D [25(OH) D] concentrations was compared in inhabitants of humid-rainy, cold-mountainous, and sunny regions. Results: Vitamin D deficiency was documented in 40% of participants including 40.70% of boys and 39.30% of girls. We found significant difference in 25(OH) D concentrations among participants living in the three different climates of the living area (P<0.05). The median inter-quartile range (IQR) level for 25(OH)D was lower in humid-rainy climate: 11.40 (18.64). Hypovitaminosis D was more frequent in humid-rainy climate (42.30%), compared to other climates; this difference was more prominent in urban areas (P<0.05). Boys living in various climates had significantly different levels of 25(OH) D(P<0.05), however this figure was not significantly different for girls (P>0.05). The highest frequency of hypovitaminosis D (45.2%) was documented among boys living in humid-rainy regions. Conclusion: The high prevalence of hypovitaminosis D, notably among inhabitants of humid-rainy region underscores the necessity of implementing national preventive strategies. This is of great importance especially in regions with lower exposure to sunlight.