Context: The role of vitamin D in the development of type 1 diabetes (T1D) remains controversial.
Objective: The objective of the investigation was to study whether there are detectable differences in serum 25-hydroxyvitamin D (25[OH]D) concentrations between children who later progressed to T1D (cases) and matched children who remained nondiabetic and negative for islet autoantibodies (controls) when followed up from birth until disease onset.
Design: A total of 3702 prospective serum samples from 252 children were measured for 25(OH)D from the age of 3 months onward using an enzyme immunoassay. Differences between the groups were compared by the mixed-model analysis of variance.
Setting: T1D prediction and prevention study clinics in Turku, Oulu, and Tampere University Hospitals, Finland, participated in the study.
Participants: By the end of 2012, all 126 case children were diagnosed with T1D. The control children (n = 126) were matched for age, sex, study site, and human leukocyte antigen-HLA-DQ-conferred risk for T1D.
Main outcome measure: Median circulating 25(OH)D concentration (nanomoles per liter) was measured.
Results: The patterns of variation in circulating 25(OH)D concentrations were similar between cases and controls and did not correlate with the age at seroconversion to autoantibody positivity (P = .79) or disease onset (P = .13). The median concentration of all collected samples did not differ between case and control children (66.6 nmol/L [range 14.0-262.8] vs 67.4 nmol/L [range 19.9-213.0]) P = .56).
Conclusions: This study shows that serum 25(OH)D concentrations are not associated with the development of T1D in Finland.