Vitamin D Supplementation of 7–8 Years Old Children from Different Geographical Areas (48–52° North Latitude): Cross Sectional Study

Background. The prevalence of vitamin D deficiency in children by their geographic latitude of residence requires follow-up study. This is crucial for implementation of preventive measures that can reduce the risk of developing pathological conditions associated with vitamin D deficiency.Objective. The aim of the study is to study the vitamin D supplementation of 7–8 years old children living in different geographical latitudes of one subject of Russian Federation.Methods. The study included relatively healthy children living in three geographical areas (northern — 52°, central — 50°, southern — 48°) of one region (Khabarovsk Krai). Vitamin D supplementation was evaluated by 25(OH)D serum concentration via enzyme-linked immunosorbent assay. Vitamin D insufficiency was diagnosed at 25(OH)D concentration of 21–30 ng/ml, deficiency — 10–20 ng/ml, severe deficiency — < 10 ng/ml; optimal 25(OH)D concentration was considered as 30–100 ng/ml.Results. The increase in prevalence of vitamin D deficiency and insufficiency has been revealed with gradual increase from southern (57%) to central (73%) and northern (83%) geographic areas in 7–8 years old children living in the same region. The prevalence of vitamin D deficiency and insufficiency (25(OH)D ≤ 30 ng/mL) among children living in the northern geographic area was greater by 3.8-fold (95% confidence interval 1.2–12.7) then among peers living in the southern areas.Conclusion. One factor affecting 25(OH)D serum concentration in children of this region is the insolation level determined by the geographical latitude of residence. The 4°N difference is significant in determining vitamin D status in residents of relatively high latitudes. Further studies of factors associated with 25(OH)D concentration in children living in different latitudes are required (insolation level, number of sunny days per year, food and household characteristics in families).