Efficacy of vitamin D food fortification and biofortification in children and adults: a systematic review protocol

Objective: The objective of this review is to assess the effect of vitamin D food fortification and biofortification on serum 25-hydroxyvitamin D (25(OH)D) concentrations. Introduction: Vitamin D deficiency is a global issue with considerable implications for public health. Many people do not receive sufficient sun exposure for adequate endogenous vitamin D synthesis, nor sufficient dietary vitamin D to meet their requirements. Increasing sun exposure may increase the risk of skin cancer, and vitamin D supplementation is not favored as a population-wide solution. Previous systematic reviews have shown a dose-dependent effect of vitamin D-fortified foods on circulating 25(OH)D concentrations. However, previous reviews did not investigate the efficacy of vitamin D fortification and biofortification in children, and several new fortification and biofortification trials in adults have been published since these earlier systematic reviews were conducted. Inclusion criteria: This review will consider randomized controlled trials that investigate the effect of vitamin D food fortification and biofortification on serum 25(OH)D concentrations in children and adults. Methods: CINAHL, MEDLINE, Embase, Cochrane Central Register of Controlled Trials, and PubMed will be searched for relevant studies published in English. Following a screening of titles and abstracts by a single author, relevant full-text articles will be independently reviewed by two authors. Two authors will independently assess methodological quality using the JBI critical appraisal checklist for randomized controlled trials. Data will be independently extracted by two authors. A meta-analysis will be conducted, and heterogeneity will be statistically tested. Systematic review registration number: PROSPERO CRD42020145497