The prevalence of vitamin D deficiency and the factors affecting vitamin D levels in children admitted to the outpatient clinic of pediatric endocrinology in Bolu Province

Background: The present study aimed to determine the rate of vitamin D deficiency in children who presented to the pediatric endocrinology outpatient clinic in Bolu and to investigate the factors affecting vitamin D levels.Methods: Vitamin D levels of 1008 children and adolescents were retrospectively analyzed according to age group (0-1, 1-10, and 10-18 years), gender, season, month, obesity and other diseases, and deficiency category. Moreover, calcium, phosphorus, alkaline phosphatase, and parathyroid hormone levels were evaluated. Comparisons and correlation analyses between related groups were performed.Results: The mean vitamin D level of the patients was 16.35 +/- 9.56 ng/mL and was lower in girls (14.90 +/- 9.56 ng/mL) than in boys (18.68 +/- 9.63 ng/mL, p<0.001). Overall, 18.3% of the children and adolescents had vitamin D insufficiency, 52.3% had vitamin D deficiency, and 3.5% had severe vitamin D deficiency. Vitamin D levels were lower in 10-18-year age group than in the other age groups (p<0.001), and levels were higher in summer and autumn than in winter and spring (p<0.001). Vitamin D levels of participants with obesity (14.3 +/- 8.3 ng/mL) were significantly lower than normal-weight participants with no health problems (15.9 +/- 8.3 ng/mL, p = 0.004). There was a negative correlation between vitamin D, alkaline phosphatase, and parathyroid hormone levels in the 1-10-year age group, but a positive correlation between vitamin D, alkaline phosphatase, and calcium levels in the 10-18-year age group.Conclusion: The rate of vitamin D deficiency is high among children and adolescents who presented to the endocrine outpatient clinic in Bolu. The season appears to be an important factor affecting vitamin D levels as well as the relationship between vitamin D and parathyroid hormone. Obese children and adolescents living in this region may be advised to take vitamin D supplements in winter and spring.