Adherence to vitamin D supplementation guidelines in children under five years of age: a systematic literature review.

There is generally poor adherence to vitamin D supplementation guidelines in children under five years of age. Nevertheless, the evidence comes from a limited number of studies, mainly conducted in infants, with high methodological heterogeneity in terms of the vitamin D supplementation guideline assessed and the definition of supplementation adherence in the study population. Further research is warranted to identify effective health promotion interventions to increase supplementation adherence and reduce the risk of vitamin D deficiency at this critical life stage.