Recent studies suggest that glycemic variability (GV) could influence the risk of complications in diabetes, independently from glycemic control (GC). GV is the evaluation of the daily fluctuations of glycemia through specific calculations. The few studies that have assessed the effects of supplementation with vitamin D (VD) in patients with diabetes type 1(DM1) on GC are controversial and there is no data about a possible action of VD on GV in these patients. Our study aims to evaluate the effects of VD supplementation on GV in patients with DM1. We executed a prospective, controlled study with 22 patients with DM1. Doses of either 4.000 or 10.000 IU/day of cholecalciferol were administered for 12 weeks according to the patient’s previous vitamin D serum levels. All patients were submitted to continuous glucose monitoring system (CGMS) with the analysis of 41.000 glycemias, dosage of vitamin D and HbA1c before and after the treatment. When the pre and post treatment variables were compared, no differences were observed, except for the expected improvement of the levels and status of VD (26,1 ± 9,0 vs 44,4 ± 24,7 ng/mL ; p<0,01 e 1,00 ± 0,76 vs 0,36 ± 0,66 ; p<0,01), respectively. Correlations were found between the percentage variation (Δ) of the glycemia standard deviation (ΔGSD), calculated using the CGMS, with Δ of the basal (r= 0,6; p<0,01) and total insulin (r= 0,6; p<0,01). Our study also found a correlation between the VD status after supplementation and Δ of the prandial (r= 0,5; p<0,05) and total insulin (r= 0,4; p<0,05), indicating that the better the vitamin D status, lower the doses of insulin needed by the patients. To efficiently study the GV, patients were divided in two groups: Patients in which the ΔGSD improved (group 1; N= 12 (55%)) and those in which the ΔGSD worsened (group 2; N= 10 (45%)). Group 1 when compared to group 2 showed lower needs of insulin (Δbasal insulin = -8,0 vs 6,3%; (p<0,05)) and lower frequency of hypoglycemia (12/44 (27%) vs 21/33 (64%), hypoglycemias / days evaluated ; p<0,01). Our data suggests that supplementation of VD on patients with DM1 could improve the GV associated to a lower need of insulin in more than 50% of these patients. The improvement of GV was strongly associated with reduction in frequency of hypoglycaemia. However, it was not possible to demonstrate benefits of vitamin D on glycaemic control measured by the HbA1c.
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