Vitamin D Status and Immune Health Outcomes in a Cross-Sectional Study and a Randomized Trial of Healthy Young Children

In young children, the relationship between vitamin D and biomarkers of immune function is not well elucidated. The objective was to investigate relationships between vitamin D and immune function in young children. Data were from a cross-sectional study (study 1) of healthy children 1.8–5.9 years (n = 457) and a 12 weeks trial using vitamin D fortified foods (study 2) in healthy 1.8–8.7 years old (n = 77) in Montreal, Canada. Vitamin D status and ex vivo immune function were assessed. In study 1 (male: n = 242; 53%), plasma IL-6, TNFα and CRP were significantly higher (p < 0.05) in children with 25-hydroxyvitamin D (25(OH)D) ≥ 75 nmol/L compared to <50 nmol/L. In study 2 (male: n = 40; 52%), there were no differences in illness outcomes (duration, number of reported illnesses, etc.) among groups. In a 6–8 years old sub-group, only the peripheral blood lymphocytes were higher in the 600 IU/day vitamin D group compared to control (percent of white blood cells; control: 41.6 ± 8.0%, 600 IU/d: 48.6 ± 8.5%). IL-6 production (but not other cytokines) by isolated mononuclear cells, after ex vivo mitogen stimulation, was lower in the intervention groups compared to the control group at 12 weeks. In conclusion, in healthy young children with sufficient vitamin D status, increasing vitamin D intakes does not confer additional advantage to immune function.