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Most People with Type 1 Still Producing Insulin

If you have Type 1 diabetes and are out of the “honeymoon period,” you’ve probably been told that your pancreas has stopped producing insulin. But it turns out that information may be wrong. Many people with Type 1 still produce at least some insulin, even years after diagnosis.

Traditionally, doctors and researchers believed that the pancreas “crashed and burned,” rapidly declining in its ability to secrete insulin as early as a year after the onset of Type 1. What new research now shows is that many people with Type 1 produce at least some level of insulin for decades after diagnosis.1,2 Your pancreas could be functioning for decades, not just one or two years after your diagnosis.

In our study of nearly 200 patients who had been living with Type 1 for nearly two decades, we saw that C-peptide secretion (a sign of insulin production) decayed gradually over 20 years, and we were able to detect C-peptide in nearly two-thirds of the blood samples we analyzed. So, why did we think for so long that people with Type 1 don’t produce any insulin? And what changed?

One major reason is that, until recently, we couldn’t detect the insulin being produced by people who long have had Type 1 diabetes, since they are producing C-peptide at lower levels than most current tests can measure. However, new ultra-sensitive blood tests for C-peptide are able to pick up very low levels of secretion, and they are now what we use in our laboratory for all of our Type 1 diabetes studies.

Right now, the greatest impact of our ability to detect C-peptide will be on Type 1 diabetes research. Most Type 1 diabetes clinical trials have been directed at patients who have recently weathered the onset of the condition. The rationale—which we now know is mistaken—was that we only had a short time to try and save the pancreas before it turns off forever. With new data that insulin secretion can persist for decades—and new tools to detect it using ultrasensitive blood tests—we can now also look at people who are well past the honeymoon stage to see if they, too, might benefit from new treatments to stop pancreas destruction and boost or preserve insulin secretion.

Our research is also beginning to show that we can identify patients who might be at highest risk of long-term complications based on their levels of insulin production, which could lead to better care, as well as clinical trial designs that focus on the most at-risk patients.

Although you won’t find ultrasensitive C-peptide tests at your doctor’s office just yet, we hope that they will start to be used in diabetes clinics in the future, especially to identify people at greatest risk for long-term complications. We also hope that patients with longstanding Type 1 diabetes will now be given the same opportunity as individuals recently diagnosed with Type 1 to participate in clinical trials.


  1. Wang L, Fraser Loverjoy N, Faustman DL. Persistence of Prolonged C-peptide Production in Type 1 Diabetes as Measured with an Ultrasensitive C-peptide Assay. Diabetes Care 2012;35:1-6.
  2. Oram RA, Jones AG, Besser REJ et al. The majority of patients with long-duration type 1 diabetes are insulin microsecretors and have functioning beta cells. Diabetologia 2014;57(1):187-91.

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Denise Faustman, MD, PhD, is a noted type 1 diabetes researcher. She is currently leading a clinical trial program at Massachusetts General Hospital to test an inexpensive vaccine, BCG, as a treatment for patients with longstanding type 1 diabetes.

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