Table 1: Studies on the association between vitamin D (25OHD) levels and glucose control in children and adolescents with Type 1 Diabetes (T1D).

Study Participants Vitamin D Supplementation Mean 25OHD Levels After Supplementation 25OHD
>75 nmol/l
(% subjects)
Association 25OHD/HbA1c Association Supplementation/HbA1c Results
Savastio et al. [13] 141 T1D (35 migrants, 106 Italians) Subjects with 25OHD <75 nmol/l
Cholecalciferol 1000 IU/day
56.6±23.7 nmol/l 20.6% + + At baseline: significant inverse correlation between 25OHD levels and diabetic keto-acidosis severity.
Relationship between HbA1c and 25OHD levels in a multivariate regression analysis.
Talaat et al. [63] 250 T1D and 250 healthy controls None / / + Not evaluated Significant negative relationship between 25OHD levels and HbA1c values.
Levels of islet antibodies, anti-GAD antibodies and anti-insulin antibodies were significantly associated with 25OHD deficiency.
Significant association between 25OHD deficiency and high levels of pro-inflammatory cytokines.
Nwosu et al. [68] Total population:
88 T1D, 43 T2D
Subjects with 25OHD <50 nmol/l:
33 T1D, 31 T2D
Subjects with 25OHD <50 nmol/l
Ergocalciferol or cholecalciferol
400-7.000 IU/day for 8-16 weeks
67.6±20.6 nmol/l
60.7±27.7 nmol/l
Not reported Not evaluated - No changes in total daily dose of insulin per kg body weight in T1D and T2D.
Significant decrease in HbA1c in T2D after 3 months of vitamin D supplementation but not in T1D.
Al Sawah et al. [69] 197 T1D None / / - Not evaluated No differences in HbA1c across 25OHD levels (≤50; 50-75; >75 nmol/l).
Not significant correlation between 25OHD and HbA1c in the multivariate model.
Perchard et al. [70] Total population:
51 T1D (35 Caucasian, 11 South Asian, 5 other)
Subjects with 25OHD <50 nmol/l:
40 T1D
Subjects with 25OHD <50 nmol/l
100.000 IU (2-10 years)-160.000 IU (>10 years) single dose
Not reported Not reported Only in white Caucasian subgroup - At baseline: no significant correlation between 25OHD and HbA1c in the whole cohort. Significant inverse relationship between 25OHD and HbA1c in the Caucasian group.
After treatment: no difference in HbA1c at 3 months or at 1 year.
Giri et al. [71] Total population:
271 T1D
Subjects with 25OHD <50 nmol/l:
124 T1D
Subjects with 25OHD <50 nmol/l
Cholecalciferol 400 IU (25OHD 30-50 nmol/l)-6.000 IU (25OHD <30 nmol/l)/day for 3 months
65.3±9.3 nmol/l Not reported + + Significant positive association between baseline HbA1c and HbA1c reduction after treatment.
Significant direct relationship between baseline 25OHD levels and HbA1c reduction after treatment.

Legend: GAD, Glutamic Acid Decarboxylase; HbA1c, glycated hemoglobin; T1D, Type 1 Diabetes; T2D, Type 2 Diabetes; 25(OH)D, 25-hydroxyvitamin D.