- βPeople with C-peptide β₯100 pmol/l were 5x more likely to keep dangerous low blood sugar time under 4%
- βHigher C-peptide was linked to 10% more time in the healthy blood sugar range
- βC-peptide β₯100 pmol/l nearly doubled the likelihood of achieving a target HbA1c below 7% (53 mmol/mol)
- βLess glucose variability means steadier, more predictable blood sugars day to day
- βA simple blood test could help doctors personalise diabetes treatment plans
| Journal | Diabetologia |
| Year | 2026 |
| PMID | 41165798 |
What This Study Found
Researchers in the UK studied 945 adults with type 1 diabetes to see whether having even a small amount of remaining insulin-producing ability β measured by a protein called C-peptide β was linked to better blood sugar control as shown by continuous glucose monitors (CGMs).
What Is C-Peptide?
When your pancreas makes insulin, it also releases C-peptide in equal amounts. So measuring C-peptide in your blood tells doctors how much insulin your body is still producing on its own. In type 1 diabetes, this natural insulin production usually declines over time, but some people retain small amounts for many years.
Key Findings
People with higher C-peptide levels (β₯100 pmol/l) had noticeably better CGM results compared to those with very low or undetectable levels:
- More time in range: 55% vs 45% for those with the lowest C-peptide
- Less time dangerously low: 1% vs 2% time below range
- Less glucose variability: Steadier blood sugars throughout the day
- Less time dangerously high: 10% vs 20% time above 13.9 mmol/l
- Better HbA1c: Nearly twice as likely to achieve an HbA1c below 53 mmol/mol (7%)
- 5x more likely to keep time-below-range under the recommended 4% threshold
Who Was More Likely to Have Residual Insulin Production?
People who retained more C-peptide tended to:
- Have been diagnosed with diabetes more recently
- Have been older when they were first diagnosed
- Be male
Why Does This Matter for You?
This research suggests that even a small amount of natural insulin production can meaningfully improve your blood sugar management. The key threshold appears to be 100 pmol/l β above this level, the benefits become clinically significant.
Importantly, the researchers say this supports efforts to protect and preserve remaining beta cells (the cells in your pancreas that make insulin). It also suggests that a simple C-peptide blood test could help doctors personalise your diabetes treatment plan.
What This Means in Practice
If you have type 1 diabetes, ask your doctor about having a C-peptide test. Knowing your level could help explain your blood sugar patterns and guide decisions about your treatment. Scientists are also actively working on ways to slow the loss of beta cell function in type 1 diabetes.