Vitamin D intakes and health outcomes in infants and preschool children: Summary of an evidence report

Systematic review evidence report of trials and prospective observational studies in generally healthy infants and preschool children aged 0-4 years. The intervention evidence included 53 active vitamin D supplementation arms across 28 studies, with most studies enrolling infants with mean ages from 0 to 12 months and one study with mean age 2.7 years.

Vitamin D supplementation, primarily vitamin D3 or vitamin D2, was given orally, usually daily, at doses ranging from 400 IU/day to 1,200 IU/day across studies; some trials used weekly, monthly, bolus, or fortified-food regimens. Examples included 1,200 IU/day versus 400 IU/day, 1,400 IU/week, 100,000 IU of vitamin D3 every 3 months, and fortified foods providing 80-1,000 IU/day.

Daily vitamin D supplementation reliably increased serum 25(OH)D concentrations, but the evidence did not establish a causal clinical benefit for most health outcomes in generally healthy infants and young children. In dose-response meta-regression, each 100 IU/day increase in supplementation was associated with a 1.92 nmol/L higher achieved 25(OH)D concentration (95% CI 0.28, 3.56; p = .022; I2 = 99.39%; n = 53 intervention arms). Most infectious disease outcomes showed no between-group difference, and growth and bone findings were mixed, with only isolated studies showing benefit. Evidence on adverse effects such as hypercalcemia and hypercalciuria was very low certainty.

Certainty was low or very low for most outcomes, and heterogeneity was substantial for the 25(OH)D dose-response analysis. Vitamin D status definitions and assay methods varied, outcome reporting was inconsistent, and several trials were too sparse for quantitative synthesis. Findings are also indirect for many clinical endpoints because studies used different doses, durations, and cointerventions, including some combined vitamin D and calcium regimens.