Association of vitamin D deficiency with severity of acute respiratory infection: A case-control study in New Zealand children

Background: Acute respiratory infections (ARI) are a major source of childhood morbidity and excess winter hospitalisations. Vitamin D modulates innate immunity with recent associations demonstrated between vitamin D deficiency and several respiratory illnesses. Objective: We evaluate the association of blood 25(OH)D 3 with ARI severity in early childhood, hypothesising that children hospitalised with ARI have lower levels of vitamin D. Methods: We conducted an unmatched case-control study of children aged <2-years in Wellington, New Zealand (NZ) over three successive years. Cases (severe) were children requiring hospitalisation for ARI, with controls (mild) attending one of five GP clinics for ARI (with no prior ARI admission). 25(OH)D 3 was collected by finger or heel prick as dried blood spots and analysed by LC-MS/MS. Results: 25(OH)D 3 was obtained in 469 children (227 cases, 242 controls) with levels (median, interquartile range) of 48 (24-65) nmol/L among cases and 52 (31-67) nmol/L among controls. Only 74 (16%) children had levels ≥75nmol/L. 60 (26%) cases and 42 (17%) controls were deficient (25(OH)D 3 levels <25 nmol/L). Cases had significantly higher odds of deficiency than controls after adjustment for age; gender; ethnicity; presentation month; total breastfeeding duration; individual deprivation; passive smoke exposure; gestational age; delivery method; and maternal atopy (OR= 1.76; 95%CI: 1.05-2.97). Conclusion: Vitamin D deficiency was more frequent among children hospitalized for ARI, as compared to those with outpatient ARI. Vitamin D status may contribute to ARI severity amongst NZ children.