Chronic administration of pharmacologic doses of vitamin E improves the cardiac autonomic nervous system in patients with type 2 diabetes

Type 2 diabetes is associated with elevated oxidative stress and declines in antioxidant defense. The disease is also characterized by an imbalance in the ratio of cardiac sympathetic to parasympathetic tone. Antioxidants, vitamin E in particular, may have beneficial effects on the cardiac autonomic nervous system through a decline in oxidative stress. We investigated the possible effects of vitamin E on the cardiac autonomic nervous system, as assessed by analysis of heart rate variability, in patients with type 2 diabetes and cardiac autonomic neuropathy. In a double-blind randomized controlled trial, 50 patients with type 2 diabetes were assigned to treatment with vitamin E (600 mg/d) or placebo for 4 mo. The anthropometric characteristics of the patients remained unchanged throughout the study. Chronic vitamin E administration was associated with decreases in concentrations of glycated hemoglobin (P < 0.05), plasma insulin (P < 0.05), norepinephrine (P < 0.03), and epinephrine (P < 0.02); a lower homeostasis model assessment index (P < 0.05); and improved indexes of oxidative stress. Furthermore, vitamin E administration was associated with increases in the R-R interval (P < 0.05), total power (P < 0.05), and the high-frequency component of heart rate variability (HF; P < 0.05) and decreases in the low-frequency component (LF; P < 0.05) and the ratio of LF to HF (P < 0.05). Finally, change in the plasma vitamin E concentration was correlated with change in the LF-HF ratio (r = -0.43, P < 0.04) independently of changes in the homeostasis model assessment index and plasma catecholamines concentrations. Chronic vitamin E administration improves the ratio of cardiac sympathetic to parasympathetic tone in patients with type 2 diabetes. Such an effect might be mediated by a decline in oxidative stress.