Inverse relationship of serum HDL and HDL2 cholesterol to C-peptide level in middle-aged insulin-treated diabetics

Serum lipids and lipoproteins were measured in 170 insulin-treated diabetics (90 females, 80 males) and in 124 nondiabetic control subjects (59 females, 65 males) aged 45 to 64 years. Plasma C-peptide response to intravenous (IV) glucagon was measured in order to classify the patients according to their capacity of endogenous insulin secretion. In both sexes, HDL and HDL2 cholesterol were higher in diabetics with no C-peptide response than in controls, whereas diabetics with high C-peptide response (postglucagon C-peptide level greater than 0.60 nmol/L) showed lower levels of HDL and HDL2 than nondiabetic controls. When adjustment for age, alcohol consumption, physical activity, body mass index, and insulin dose was made by analysis of covariance, the highly significant difference in HDL and HDL2 cholesterol level between diabetics with no C-peptide response and diabetics with high C-peptide response still remained in both sexes. This study gives support to the hypothesis that elevated HDL and HDL2 cholesterol levels in insulin-treated diabetics are not explained by effects of treatment with exogenous insulin, but rather are associated with the type of diabetes characterized by deficient endogenous insulin secretion.