# C-peptide

C-peptide is a 31-amino-acid chain. It is cut out of proinsulin inside your pancreatic beta cells. One C-peptide is released for every insulin molecule. So your fasting C-peptide directly reflects how much insulin you make yourself. The liver barely clears it, so it lasts longer than insulin (a half-life of about 30 minutes versus 3 to 5 for insulin). That makes it measurable even when you take insulin as a drug. Fasting C-peptide plays two roles. As a gauge of beta-cell reserve, low values flag lost insulin output, as in type 1 and late-stage type 2 diabetes. As a sign of chronic high insulin, high values point to insulin resistance and over-secretion. An NHANES cohort (Patel et al. 2012; 5,153 non-diabetic adults) found fasting C-peptide beat fasting insulin and resistance indexes at predicting heart and all-cause death. A meta-analysis of 23 studies (Ahmadirad et al. 2023) confirmed a 22% higher all-cause death risk (HR 1.22; 95% CI 1.12 to 1.32) and 38% higher heart death (HR 1.38; 95% CI 1.08 to 1.77). In type 1 diabetes, some leftover secretion is protective. In insulin-resistant people, a high value signals metabolic strain. You read it in clinical context (fasting glucose, HbA1c, diabetes status). It tells you most alongside fasting insulin and glucose.

## Sources

- Vejrazkova D, Vankova M, Lukasova P, Vcelak J, Bendlova B. (2020). Insights Into the Physiology of C-peptide. Physiological Research. https://doi.org/10.33549/physiolres.934519
- Patel N, Taveira TH, Choudhary G, Whitlatch H, Wu WC. (2012). Fasting Serum C-Peptide Levels Predict Cardiovascular and Overall Death in Nondiabetic Adults. Journal of the American Heart Association. https://doi.org/10.1161/jaha.112.003152
- Ahmadirad H, Teymoori F, Mokhtari E, et al.. (2023). Serum C-peptide level and the risk of cardiovascular diseases mortality and all-cause mortality: a meta-analysis and systematic review. Frontiers in Cardiovascular Medicine. https://doi.org/10.3389/fcvm.2023.1205481

---

_Canonical: https://longevity-switzerland.com/en/glossary/c-peptide · Part of Longevity Cities · Updated 2026-06-22_