Response of serum 25(OH)D to Vitamin D and calcium supplementation in school-children from a semi-rural setting in India

The objectives of this study were to: 1) Determine the impact of varying baseline serum 25OHD on increase in vitamin D concentrations after daily supplementation with vitamin D and calcium (1000 IU + 500 mg respectively) for six months in school-children from a semi-rural setting 2) Test the efficacy of daily vitamin D-calcium supplementation on improvement in serum vitamin D concentrations to ≥75 nmol/L. Data collected from 106 subjects (58 boys, 48 girls), aged 6-12 years, included anthropometric measures like height and weight, body composition analysis, three one-day dietary recalls and sunlight exposure (by questionnaire). Blood was collected at baseline and endline and estimated for serum vitamin D by ELISA technique using standard kits. Classification of Vitamin D status was performed according to the 2011 Endocrine Society Practice Guidelines: vitamin D deficiency - <50 nmol/L; insufficiency - 50.0-74.9 nmol/L; sufficiency - ≥75 nmol/L. Statistical analysis was performed using SPSS software. Mean baseline serum vitamin D concentration was 59.7 ± 11.2 nmol/L; this rose to 79.8 ± 23.3 nmol/L with no significant differences between genders at the two time-points. Inverse relationship was obtained between baseline serum 25(OH)D concentrations and change in serum concentrations after supplementation, implying that with increasing baseline serum concentrations of 25(OH)D, increase in vitamin D levels post supplementation were significantly lower (r = − 0.96, p < 0.0001). Greatest benefit of change in serum vitamin D concentrations after supplementation was experienced by children with basal concentrations of <45 nmol/L. Daily vitamin D supplementation was effective in improving serum 25(OH)D to ≥75 nmol/L in 44% of children. Significantly higher percentage of children who were deficient at baseline (64%) were able to attain serum concentrations of ≥75 nmol/L as compared to children who were vitamin D insufficient (43%) (p < 0.001). Thus, daily supplementation with 1000 IU of vitamin D along with 500 mg of calcium helped in improving serum vitamin D concentrations to ≥75 nmol/L. Children who were vitamin D deficient particularly experienced these benefits.