Background: Hospital admission for acute respiratory infections (ARIs) during early childhood is a global public health concern. Vitamin D deficiency is prevalent during pregnancy and infancy. Evidence indicates that vitamin D supplementation prevents ARIs.
Objectives: To determine whether vitamin D deficiency at birth is associated with ARI hospitalisations during infancy.
Methods: We performed a nested case-control study in children aged 0-12 months. Cases had ≥1 ARI hospitalisation and 4 controls were individually matched to each case. Newborn 25(OH)D concentration was measured on dried blood spots using two-dimensional liquid chromatography-tandem mass spectrometry. Hospital admissions were measured using health care records. Median serum 25(OH)D concentration in cases and controls was compared, and covariates of ARI hospitalisation during infancy were assessed using conditional logistic regression analysis.
Results: Six per cent of the cohort (n = 384) had an ARI hospitalisation during infancy, and 1536 controls were matched to cases. Median DBS [25(OH)D] was lower among ARI cases than controls (46 nmol/l vs. 61 nmol/L). Median 25(OH)D levels were lower for those hospitalised ≥2 times (47, IQR 36, 58) vs. those hospitalised once (52, IQR 42, 62) vs. the controls and also lower for those who stayed in the hospital for ≥3 days (45, IQR 36, 54) vs 1-2 days (48, IQR 38, 59) compared to the controls. After adjustment for season of birth and covariates describing demographic, antenatal, perinatal, and infant characteristics, DBS 25(OH)D concentration (<50 nmol/L) at birth was associated with increased odds of ARI hospitalisation during infancy (odds ratio 2.20, 95% confidence interval 1.48, 2.91).
Conclusions: Vitamin D deficiency at birth is associated with increased odds of ARI hospitalisations in infants. The findings have implications for a developed country like New Zealand where vitamin D supplementation is not routinely recommended and the burden of ARI hospitalisation in young children is high.
Keywords: case-control studies; cohort studies; hospitalization; infant; respiratory tract infections; vitamin d.
© 2021 John Wiley & Sons Ltd.