Vitamin D and cardiovascular autonomic neuropathy in type 2 diabetes mellitus according to diabetic kidney disease stage

Background/objectives: Cardiovascular autonomic neuropathy (CAN) may be associated with other diabetes mellitus-related complications. In addition, lower vitamin D (VD) levels have been associated with diabetic kidney disease (DKD) and diabetic neuropathy. We evaluated the relationship between serum VD and CAN in patients with type 2 Diabetes Mellitus (T2DM) in early and advanced stages of DKD. Methods: Seventy-six T2DM patients, 28 in early DKD stage (urine albumin to creatinine ratio (UACR)): 30 to 299 mg/g - group 1), and 48 in advanced DKD stage (UACR ≥300 mg/g - group 2), participated. Results: In group 1, prevalence of CAN was 46% versus 75% in group 2 (p=0.01). 25(OH)D was lower in group 2 (26.3 ± 9.8 vs 30.0 ± 8.0; p<0.05) and, in this group, those with CAN vs without CAN showed lower 25(OH)D (27.8 ± 8.3 vs 32 ± 6.3; p<0.05). Only in group 2, patients with VD deficiency (<no><20</no> ng/ml) vs normal, showed worse CAN parameters, particularly VLF (65.5 (46-104) vs 309 (106.5-682.5), p<0.01), SDNN (10.5 (8-17.5) vs 28.5 (13-48), p<0.05) and Valsalva Maneuver (1.12 ± 0.04 vs 1.30 ± 0.21, p<0.05). We have found a correlation between VD concentration and CAN prevalence (r = -0.3, p<0.05). Logistic regression showed that VD concentration <no><20</no> ng/ml increased 24 times the chance of abnormal VLF (R²: 0.38; OR: 24.1; 95% (CI: 2.6-222); p<0.01). Conclusions: To our knowledge, this is the first study to demonstrate an association between lower VD and CAN in T2DM and advanced DKD.