Correlation of fasting serum C-peptide and insulin with markers of metabolic syndrome-X in a homogenous Chinese population with normal glucose tolerance

We surveyed 1447 men and 1800 women aged 30 years (mean 46.7 years) with normal glucose tolerance in Kin-Chen, Kinmen. Correlations of fasting serum insulin and C-peptide with various clinical and biochemical parameters were analyzed by multiple linear regression analysis. Women had significantly higher levels of insulin than men (98+/-43 vs. 91+/-43 pM, p<0.0001), yet they also had a more favorable cardiovascular risk profile. Insulin was positively associated with the female sex, height, body mass index, waist-to-hip ratio, serum triglyceride, total cholesterol, uric acid, and fasting plasma glucose, and was negatively associated with age, smoking, and high-density lipoprotein cholesterol. Independent correlates for C-peptide were similar to those of insulin, except for the addition of mean blood pressure and the exclusion of age and total cholesterol. Significant interaction of sex-body mass index (coefficient = -0.0051, p = 0.0232) was detected for C-peptide only. In conclusion, both fasting serum insulin and C-peptide are quantitatively associated with cardiovascular risk factors in this homogeneous Chinese population with normal glucose tolerance. The female sex is independently associated with higher insulin and C-peptide levels, and the strength of the positive association between the female sex and C-peptide reduces when the body mass index increases.