Cord blood vitamin D and the risk of acute lower respiratory infection in Indigenous infants in the Northern Territory

Objectives: To assess vitamin D status in Indigenous mothers and infants in the Northern Territory, and to determine whether cord blood vitamin D levels are correlated with the risk of infant hospitalisation for acute lower respiratory infection (ALRI).

Design and participants: Within a nested cohort of 109 Indigenous mothereinfant pairs recruited between 2006 and 2011, we used liquid chromatographyemass spectrometry to measure vitamin D (25(OH)D₃) levels in maternal blood during pregnancy (n=33; median gestation, 32 weeks [range, 28-36 weeks]) and at birth (n=106; median gestation, 39 weeks [range, 34-41 weeks]), in cord blood (n=84; median gestation, 39 weeks [range, 36-41 weeks]), and in infant blood at age 7 months (n=37; median age, 7.1 months [range, 6.6-8.1 months]).

Main outcome measure: ALRI hospitalisations during the first 12 months of infancy, identified using International Classification of Diseases coding (J09-J22, A37-A37.9).

Results: Compared with mean 25(OH)D₃ levels in maternal blood during pregnancy (104 nmol/L), mean levels were 23% lower in maternal blood at birth (80 nmol/L) and 48% lower in cord blood samples (54 nmol/L). The mean cord blood 25(OH)D₃ concentration in seven infants subsequently hospitalised for an ALRI was 37 nmol/L (95% CI, 25-48nmol/L), lower than the 56nmol/L (95% CI, 51-61 nmol/L) in the 77 infants who were not hospitalised with an ALRI (P=0.025).

Conclusions: Cord blood 25(OH)D₃ concentrations were about half those in maternal blood during the third trimester of pregnancy (about 7 weeks earlier). Most cord blood levels (80%) were classified as vitamin D insufficient (< 75 nmol/L) by existing guidelines, and were lower among infants who were subsequently hospitalised with an ALRI.