Antioxidant defences are reduced during the oral glucose tolerance test in normal and non‐insulin‐dependent diabetic subjects

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Abstract
Free radical production has been reported to be increased in patients with diabetes mellitus, and it has been suggested that hyperglycaemia may directly contribute to the generation of oxidative stress. The aim of the present study was to evaluate the effects of an acute increase in glycaemia on plasma antioxidant defences. During the oral glucose tolerance test (OGTT), plasma concentration of protein-bound sulphydryl (SH) groups, vitamin C, vitamin E and uric acid significantly decreased in normal as well as non-insulin-dependent diabetes mellitus (NIDDM) subjects. Total plasma radical-trapping activity, which evaluates plasma antioxidant capacity due to known and unknown antioxidants present in the plasma as well as their mutual co-operation, was also significantly reduced. This finding supports the hypothesis that hyperglycaemia may, even acutely, induce an oxidative stress.