Does residual insulin secretion (assessed by C-peptide concentration) affect lipid and lipoprotein levels in insulin-dependent diabetes mellitus?

1. Residual endogenous insulin secretion can be assessed by the circulating C-peptide concentration and is present in up to 15% of subjects with established insulin-dependent diabetes mellitus (IDDM). Its role in lipid metabolism in IDDM is not clearly defined. We examined the relationships between serum lipid and lipoprotein concentrations and the response of circulating C-peptide to a test meal in 205 subjects with IDDM. 2. Lipid and lipoprotein levels and glycaemic control did not differ significantly between patients with undetectable, low or high C-peptide responses. 3. High density lipoprotein (HDL) cholesterol and its subfractions were inversely related to concentrations of serum triacylglycerols (P less than 0.01-0.001), but not to C-peptide or glycated haemoglobin (HbA1) levels. Levels of HbA1 and triacylglycerols were correlated with one another (P less than 0.01). Analysis of variance revealed that differences in gender and triacylglycerol concentrations were the most important determinants of HDL and HDL2 cholesterol levels. C-peptide only exerted a weak effect on HDL2 cholesterol levels and no significant predictors of HDL3 cholesterol were found. 4. It is concluded that endogenous insulin secretion (assessed by C-peptide concentration) is relatively unimportant in modifying HDL metabolism in IDDM and that associated clinical features, in particular ambient hypertriglyceridaemia, are of greater importance.