Background and rationale
ARIs
ACUTE RESPIRATORY INFECTIONS
Acute respiratory infections (ARIs) remain the greatest global cause of childhood morbidity and mortality.Vitamin D is a steroid-like molecule generated predominantly on exposure of skin to sunlight with the remainder coming from the diet.Most immune cells express both the VDR and the enzymes (1α-hydroxylase) necessary to locally convert circulating 25OHD into active 1,25OHVitamin D deficiency (<50 nmol/L) is prevalent in many populations globally and has been repeatedly linked to an increased risk of childhood ARI.To address deficiency in pregnancy, doses of 2000–4000 IU/day from 12 to 16 weeks gestation have been shown to be safe and effective.A 2017 meta-analysis of individual-level data from 10 933 participants in 25 randomised controlled trials (RCTs)