English abstract
Introduction: An increased prevalence of vitamin D deficiency and/or insufficiency in patients with type 1 diabetes mellitus (TIDM) has been reported worldwide. Moreover, patients with TIDM and microalbuminuria have been reported to have lower vitamin D levels than those with normoalbuminuria. Vitamin D treatment has also been shown to improve glycemic control and insulin sensitivity in people with TIDM.
Objective: To estimate the level of vitamin D in TIDM. To correlate body mass index (BMI), glucose, HbAIC and urine vitamin D binding protein (UVDBP) excretion with vitamin D status in TIDM.
Method: We examined 67 subjects with TIDM, aged 9.742.5 yr, along with 65 healthy control subjects, and aged 9.62.5 yr. We measured weight, height, body mass index (BMI), serum glucose, HbAlc, lipid profile, hsCRP, serum creatinine, cystatin-C, serum total calcium, urine creatinine, serum/urine albumin, vitamin D binding protein (VDBP) in urine and serum concentrations of 25-hydroxyvitamin D (25(OH) D). The results of 25(OH) D were compared between the 2 groups and investigated for relationships with glycemic control, BMI and UVDBP excretion.
Results: 25(OH) D deficiency (<50 nmol/L, equivalent to <20 ng/mL) was prevalent in both control subjects (49%) and TIDM (43%). In TIDM with HbA1c>7.5% (this stated as group 3) significant lower concentration of 25(OH)D was found compared to TIDM with HbAlc<7.5% this stated as group 2: (2047 ng/mL vs. 25+7 ng/mL, p=0.030, respectively). Significant higher concentration of urinary excretion of VDBP was found in TIDM patients compared to control group (420,743114.485 ng/g vs. 105,2974293.309 ng/g. respectively: 0.033) and non-significant higher levels of UVDBP in the diabetic subgroup 3 compared to diabetic subgroup 2. Vitamin D was found to correlate inversely with BMI, serum glucose and HbAle. There was no significant linear relationship between UVDBP excretion and serum vitamin D. Positive correlation was found between urine excretion of VDBP and urine albumin excretion, glucose and HbAlc. Identified independent factors for urine VDBP excretion are urine albumin excretion, glucose and HbAle. Conclusion: In our study low levels of vitamin D were observed in both TIDM and control subjects. Vitamin D levels were not significantly correlated with glycemic controls However; BMI was inversely correlated with vitamin D levels in the overall subjects. In addition, urinary loss of VDBP in subjects with TIDM worsened in the presence of albuminuria. Because VDBP is critically involved in the delivery of 25(OH)D to the renal cpithelial cell of the proximal tubule for activation to 1.25(OH), D, therefore, urinary loss of VDBP might contribute to low vitamin D levels in TIDM.
