This Cochrane systematic review pooled data from 107 randomized controlled trials involving 31,521 participants to assess whether vitamin D supplementation during pregnancy or early childhood reduces acute respiratory infection (ARI) healthcare visits in children under five. Results showed a slight reduction in the proportion of children needing ARI-related visits when given vitamin D versus placebo, but no meaningful reduction in how often each child visited. Higher doses showed no advantage over lower doses. Hypercalcemia was rare across all groups. Overall evidence certainty was low to moderate, meaning larger, well-designed trials are still needed before firm recommendations can be made.
