To investigate whether serum levels of lipid peroxides measured as thiobarbituric-acid-reactive substances (TBARS) differ in type I and type II diabetic patients, whether serum levels correlate with late sequelae of diabetes, and whether serum levels of free vitamin E correlate with levels of lipid peroxidation by-products.

The relationship among lipids, glycosylated hemoglobin A_1c (HbA_1c), lipid peroxides measured as TBARS, and free vitamin E was determined in 158 patients. Fifteen of the 77 patients with type I diabetes and 39 of the 81 patients with type II diabetes had clinically apparent peripheral vascular disease or coronary artery disease, or both.

Compared with control subjects, serum levels of TBARS were found to be significantly elevated (P <0.001) in diabetic patients, and type II diabetic patients had significantly higher levels (P <0.001) than type I patients. Both type I and type II diabetic patients with good metabolic control (HbA_1c <6.5%) had significantly lower (P <0.005) TBARS levels than patients with poor metabolic control, but all groups had higher levels than the control group. Type II patients with angiopathy had significantly higher levels of TBARS than patients without angiopathy. Free vitamin E levels in control subjects and diabetic patients did not differ statistically.

Serum levels of TBARS were significantly increased in all patients suffering from diabetes mellitus, whereby TBARS levels did not depend on the total amount of circulating lipids. It can be suggested that the enhanced lipidperoxidation is contributed to an increased formation of free radicals in diabetes mellitus.