Vitamin d supplementation in pregnant or breastfeeding women or young children for preventing asthma

This is a protocol for a Cochrane Review (Intervention). The objectives are as follows: Primary objective 1. To evaluate the efficacy of vitamin D supplementation for preventing asthma in children Secondary objectives 1. To assess the efficacy of vitamin D supplementation for preventing asthma (a) in children at risk of vitamin D deficiency (as defined by trial authors) at the start of the trial or in child(ren) whose mother is at risk of vitamin D deficiency at the start of the trial, and (b) according to timing of the intervention and the cumulative dose administered 2. To assess the efficacy of vitamin D supplementation for preventing atopic dermatitis, which often precedes the development of asthma.