The relationship between vitamin D status and cardiac autonomic neuropathy in patients with type 2 diabetes mellitus.

Objective: This study evaluates cardiac autonomic neuropathy and heart rate variability according to the vitamin D status in type 2 diabetes mellitus.

Methods: A total of 163 patients were recruited. Cardiac autonomic neuropathy was assessed using five tests according to Ewing's protocol. The time and frequency domains of the heart rate variability were also evaluated. Patients were separated into three groups: vitamin D sufficient [25(OH)D ⩾ 20 ng/mL], vitamin D insufficient [10 ⩽ 25(OH)D < 20] and vitamin D deficiency [25(OH)D < 10] groups.

Results: Both standard deviation of normal-to-normal RR intervals and square root of the average of the sum of the squares of the differences between adjacent NN intervals in the supine position were significantly lower in vitamin D deficient group. Low frequency/high frequency ratio in the upright position was significantly higher in the vitamin D deficient group. 25(OH)D levels are positively correlated with standard deviation of normal-to-normal RR intervals in the supine position. In multivariate logistic analysis, patients with vitamin D levels of 10 < 25(OH)D < 20 ng/mL showed borderline significantly lower cardiac autonomic neuropathy risk than those with 25(OH)D levels <10 ng/mL (odds ratio = 0.45 (0.23-1.01), p = 0.051).

Conclusion: Vitamin D deficiency was significantly correlated with heart rate variability parameters. However, there was only borderline significant association between vitamin D concentration and presence of cardiac autonomic neuropathy. Therefore, future studies are required to establish a relationship between vitamin D levels and cardiac autonomic neuropathy.