Glycemic Variability and Insulin Needs in Patients with Type 1 Diabetes Mellitus Supplemented with Vitamin D: A Pilot Study Using Continuous Glucose Monitoring System

Background: Recent studies suggest that glycemic variability could influence the risk of complications in Type 1 Diabetes Mellitus (T1DM). There are no data about the action of Vitamin D (VD) on glycemic variability. Our pilot study aims to evaluate glycemic variability and insulin needs in patients with T1DM supplemented with VD. Methods: 22 Patients received doses of 4000 and 10000 IU/day of cholecalciferol for 12 weeks, according to the patient's baseline VD levels and underwent continuous glucose monitoring system. Results: Correlations were found between percentage variation (Delta) of glycemia standard deviation (Delta SDG), calculated using continuous glucose monitoring, with Delta of basal (r = 0.6; p < 0.01) and total insulin dose (r = 0.6; p < 0.01). Correlations between VD status after supplementation and Delta of prandial (r = 0.5; p < 0.05) and total insulin dose (r = 0.4; p < 0.05) were found, suggesting that the dose of insulin needed by patients is lower when VD status is better. We divided patients in two subgroups: SDG improved (subgroup 1; N = 12 (55%)) and SDG worsened (subgroup 2; N = 10 (45%)). Group 1, compared to subgroup 2, required a lower insulin dose (Delta basal insulin dose = -8.0 vs. 6.3%; p < 0.05) and had a lower frequency of hypoglycemia (27% vs. 64%, hypoglycemias/days evaluated; p < 0.01). Conclusion: Our study suggests a relation between VD supplementation, improved glycemic variability, lower insulin needs and lower frequency of hypoglycemia in patients with T1DM.