Plasma nitrotyrosine levels, antioxidant vitamins and hyperglycaemia

Aims Studies on plasma nitrotyrosine (NT) levels, a measure of oxidative injury, in diabetes are limited and discordant; the amount of antioxidants might represent a possible explanation for the discordant results. The aim of this paper is to evaluate the association between plasma NT levels and glucose tolerance status, according to antioxidant vitamin intakes. Methods In three hundred men randomly selected from a population-based cohort, NT levels were measured and dietary intake assessed by a food-frequency questionnaire. Results NT values were similar in patients with diabetes (n = 34), impaired fasting glucose (n = 77) and normoglycaemic subjects (n = 189). However, in subjects with lower than recommended daily intakes of antioxidant vitamins C and A, NT levels were significantly higher in the diabetic patients. In a multiple regression model, after adjustments for age, body mass index (BMI) and smoking habits, NT levels were significantly associated with fasting glucose in patients with lower intakes of vitamin C (beta = 11.4; 95% CI 1.3 21.5) and vitamin A (beta = 14.9; 95% CI 3.9 25.9), but not in subjects with lower intake of vitamin E. Conclusion A significant positive correlation between NT levels and fasting glucose is evident only in the presence of a reduced intake of some antioxidant vitamins. These findings might explain, at least in part, the discrepant results of previous studies and, if confirmed by further studies, suggest a simple measure (a balanced diet) to alleviate the increased oxidative stress of diabetes.