Association of Serum C-Peptide Concentrations with Cancer Mortality Risk in Pre-Diabetes or Undiagnosed Diabetes

BACKGROUND Known associations between diabetes and cancer could logically be attributed to hyperglycemia, hypersecretion of insulin, and/or insulin resistance. This study examined the relationship between initial glycemic biomarkers among men and women with impaired fasting glucose or undiagnosed diabetes and cancer mortality during follow up. METHODS The cohort included subjects aged 40 years and above from the Third National Health and Nutrition Examination Survey (NHANES III) with fasted serum glucose >100 mg/dl without the aid of pharmaceutical intervention (insulin or oral hypoglycemics). Cancer mortality was obtained from the NHANES III-linked follow-up database (up to December 31, 2006). A Cox regression model was applied to test for the associations between cancer mortality and fasting serum glucose, insulin, glycosylated hemoglobin (HbA1c), C-peptide, insulin like growth factor (IGF-1), IGF binding protein 3 (IGFBP3) and estimated insulin resistance. RESULTS A total of 158 and 100 cancer deaths were recorded respectively from 1,348 men and 1,161 women during the mean 134-month follow-up. After adjusting for the effect of age and smoking in women, all-cause cancer deaths (HR: 1.96 per pmol/ml, 95% CI: 1.02-3.77) and lung cancer deaths (HR: 2.65 per pmol/ml, 95% CI: 1.31-5.36) were specifically associated with serum C-peptide concentrations. Similar associations in men were not statistically significant. Serum glucose, HbA1c, IGF-1, IGFBP3 and HOMA were not independently related to long-term cancer mortality. CONCLUSION C-peptide analyses suggest a modest association with both all-cause and lung cancer mortality in women but not in men. Further studies will be required to explore the mechanisms.