Objective: This study aimed to evaluate the frequency of seasonal 25-hydroxyvitamin D [25(OH)D] deficiency and insufficiency in children and adolescents living in Bağcılar, district of İstanbul city.
Methods: Serum vitamin D levels of 280 children aged 3-17 years old were measured at the end of winter and at the end of summer. Of the total group, vitamin D levels were re-measured in 198 subjects. Vitamin D deficiency was defined as a serum 25(OH)D level less than 15 ng/mL and insufficiency-as levels between 15 and 20 ng/mL. Patients whose vitamin D levels were less than 15 ng/mL at the end of winter were treated with 2000 units/day of vitamin D for 3 months.
Results: In the "end of winter" samples, 25(OH)D deficiency was present in 80.36% of the subjects and insufficiency in 11.79%. In the "end of summer" samples, vitamin D deficiency was detected in 3.44% and insufficiency in 27.75%. Vitamin D levels in the "end of winter" samples were not significantly different between boys and girls, while "end of summer" levels were significantly lower in girls (p=0.015). Sunlight exposure was significantly higher in boys (p=0.011). The group with sufficient dairy product consumption had significantly higher vitamin D levels in both "end of summer" and "end of winter" samples. Limb pain was frequently reported in children with low vitamin D levels in the "end of winter" samples (p=0.001). Negative correlations were observed between vitamin D levels and season and also between vitamin D levels and age.
Conclusion: It is essential to provide supplemental vitamin D to children and adolescents to overcome the deficiency seen especially at the end of winter.