Plasma retinol and alpha-tocopherol concentrations in insulin-dependent diabetes mellitus: their relationship to microvascular complications.

Plasma alpha-tocopherol and retinol, both assayed by an HPLC method, have been evaluated in a group of 60 patients affected by insulin-dependent (type 1) diabetes mellitus, stratified according to the presence of retinopathy and nephropathy diagnosed by an urinary albumin excretion rate ranging between 20 and 200 micrograms/min (microalbuminaria) or > 200 micrograms/min (macroalbuminuria), all of whom were compared with 26 healthy controls strictly matched for age and sex. Plasma lipids and age were positively correlated with plasma retinol and alpha-tocopherol in both diabetic and control subjects. Either plasma retinol or its ratio to cholesterol were significantly and independently reduced in the younger subset of diabetics, as compared to controls, independently from other confounding variables, while plasma alpha-tocopherol was unchanged in diabetic subjects and in healthy controls. Retinopathy was not associated with altered levels of both plasma alpha-tocopherol or retinol. The presence of increased urinary albumin excretion was associated with higher plasma levels of alpha-tocopherol and, only for macroalbuminuria, of retinol. However, after processing the data by a multivariate model, nephropathy was characterized by an increase only in plasma alpha-tocopherol. In conclusion, according to our findings, plasma retinol is significantly decreased in younger insulin-dependent diabetic patients while alpha-tocopherol is significantly altered in diabetic patients with nephropathy.