Context: The effect of the anti-inflammatory and immunomodulatory actions of vitamin D on the duration of partial clinical remission (PR) in youth with type 1 diabetes (T1D) is unclear.

Objective: This work aimed to determine the effect of adjunctive ergocalciferol on residual β-cell function (RBCF) and PR in youth with newly diagnosed T1D who were maintained on a standardized insulin treatment protocol. The hypothesis was that ergocalciferol supplementation increases RBCF and prolongs PR.

Methods: A 12-month, randomized, double-blind, placebo-controlled trial was conducted of 50 000 IU of ergocalciferol per week for 2 months, and then once every 2 weeks for 10 months, vs placebo in 36 individuals aged 10 to 21 years, with T1D of less than 3 months and a stimulated C-peptide (SCP) level greater than or equal to 0.2 nmol/L (≥ 0.6 ng/mL). The ergocalciferol group had 18 randomly assigned participants (10 male/8 female), mean age 13.3 ± 2.8 years, while the control group had 18 participants (14 male/4 female), aged 14.3 ± 2.9 years.

Results: The ergocalciferol treatment group had statistically significantly higher serum 25-hydroxyvitamin D at 6 months (P = .01) and 9 months (P = .02) than the placebo group. At 12 months, the ergocalciferol group had a statistically significantly lower serum tumor necrosis factor α (TNF-α) concentration (P = .03). There were no statistically significant differences between the groups at each time point from baseline to 12 months for SCP concentration (P = .08), glycated hemoglobin A1c (HbA1c) (P = .09), insulin dose-adjusted A1c (IDAA1c), or total daily dose of insulin. Temporal trends for rising HbA1c (P = .04) and IDAA1c (P = .02) were statistically significantly blunted in the ergocalciferol group.

Conclusion: Ergocalciferol statistically significantly reduced serum TNF-α concentration and the rates of increase both in A1c and IDAA1c, suggesting a protection of RBCF and PR in youth with newly diagnosed T1D.