Vitamin D supplementation in early childhood and risk of type 1 diabetes: a systematic review and meta-analysis.
OBJECTIVE
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.


CONCLUSIONS
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.
Zipitis
C S
CS
Department of Paediatrics, Stockport NHS Foundation Trust, Poplar Grove, Stockport SK2 7JE, UK. czipitis@hotmail.com
Akobeng
A K
AK
D000293:Adolescent; D000367:Age Factors; D016022:Case-Control Studies; D002648:Child; D002675:Child, Preschool; D003922:Diabetes Mellitus, Type 1 / Q000178:diet therapy / Q000517:prevention & control*; D004305:Dose-Response Relationship, Drug; D006801:Humans; D007223:Infant; D014807:Vitamin D / Q000008:administration & dosage*; D014808:Vitamin D Deficiency / Q000178:diet therapy / Q000276:immunology*; D014815:Vitamins / Q000008:administration & dosage*
D014815:Vitamins; D014807:Vitamin D