The recommended dose of vitamin D3 in children aged 2-10 years is within the range 600-1000 IU/day. Despite the recommended prophylaxis, the problem of vitamin D3 deficiency increases with age.

Aim: To assess the effect of vitamin D3 supplementation in the winter-spring season.

Material and Method: 73 healthy children aged 4-10 years, supplemented with vitamin D3 at a dose of 1000 IU/day were included into the prospective 3 months intervention study. 25-hydroksyvitamin D3 [25(OH)D] was determined by the chemiluminescence method. Intake of vitamin D3, body composition (bioelectrical impedance), body weight, height and BMI were assessed.

Results: Serum 25(OH)D concentration increased from 24,81 ± 7,54 ng/ml to 35,19 ± 6, 11 ng/ml (p < 0.001) in 66 children after 3 months of supplementation. The prevalence of vitamin D3 deficiency [25(OH)D < 20 ng/ml] decreased from 22.7% to zero (p < 0.001), while the prevalence of optimal vitamin D3 status [25(OH)D ≥ 30 ng/ml] increased from 24.2% to 80.3%. Final 25(OH)D concentration corelated with baseline 25(OH)D concentration (R = 0.29; p < 0.05), vitamin D3 dose per kg body weight (R = 0,43; p < 0.05), height (R = 0.35; p < 0.05), BMI (R = -0.33; p < 0.05), body fat mass (R = -0.34; p < 0.05) and child’s age (R = 0.43; p < 0.05). In a multiple regression analysis (R2 = 0.49; p = 0.004), only an association between 25(OH)D concentration and child’s age remained significant (b = -2.1; p = 0.048). Post-supplementation 25(OH)D concentration was higher in pre-school children than school children (37,55 ± 5,79 vs 33,10 ± 5,68 ng/ml; p= 0.003).

Conclusions: Vitamin D3 supplementation at a dose of 1000 IU/day eliminates the problem of vitamin D3 deficiency and provides optimal vitamin D3 status for most children aged 4-10 years. Effect of vitamin D3 supplementation is dependent on child’s age.