Vitamin D supplementation in early childhood and risk of type 1 diabetes: a systematic review and meta analysis
Objectives: To assess whether vitamin D supplementation in infancy reduces the risk of type 1 diabetes in later life. Methods: This was a systematic review and meta analysis using Medline, Embase, Cinahl, Cochrane Central Register of Controlled Trials and reference lists of retrieved articles. The main outcome measure was development of type 1 diabetes. Controlled trials and observational studies that had assessed the effect of vitamin D supplementation on risk of developing type 1 diabetes were included in the analysis. Results: Five observational studies (four case control studies and one cohort study) met the inclusion criteria; no randomised controlled trials were found. Meta analysis of data from the case control studies showed that the risk of type 1 diabetes was significantly reduced in infants who were supplemented with vitamin D compared to those who were not supplemented (pooled odds ratio 0.71, 95% CI 0.60 to 0.84) The result of the cohort study was in agreement with that of the meta analysis. There was also some evidence of a dose response effect, with those using higher amounts of vitamin D being at lower risk of developing type 1 diabetes. Finally, there was a suggestion that the timing of supplementation might also be important for the subsequent development of type 1 diabetes. Conclusion: Vitamin D supplementation in early childhood may offer protection against the development of type 1 diabetes. The evidence for this is based on observational studies. Adequately powered, randomised controlled trials with long periods of follow up are needed to establish causality and the best formulation, dose, duration and period of supplementation.
Archives of Disease in Childhood