Type 1 Diabetes is Far More Common in Adults Than Most Realize

A new study has revealed that nearly 40 percent of Americans with type 1 diabetes were diagnosed after the age of 30.

The lead researcher believes that many clinicians are unaware of how frequently type 1 diabetes develops in adulthood, leading to misdiagnosis and suboptimal treatment for many.

Michael Fang, PhD, is an assistant professor at Johns Hopkins University’s Bloomberg School of Public Health. He and his colleagues recently published a letter in the Annals of Internal Medicine sharing the results of a new research report. Fang and his team used data from the National Health Interview Survey, a nationally representative sample, to find out what age Americans with type 1 diabetes were diagnosed.

Though type 1 diabetes onset is still widely associated with childhood, the researchers learned that more than half of type 1 diabetes cases developed in adults. 37 percent of survey participants reported that they were diagnosed after the age of 30. The sample included patients who were diagnosed as late as their seventies and eighties. The study also revealed that men and people of color tend to be diagnosed at later ages.

“I suspect American clinicians may underestimate how common adult-onset type 1 diabetes is,” Fang told Diabetes Daily.

“I think one big contributor is the misconception that type 1 diabetes is a ‘childhood disease.’ As a result of this, providers may assume that all adult patients have type 2 diabetes, even if they do not fit the ‘classic’ clinical picture of a type 2 diabetes patient.”

Misdiagnosis is shockingly common. A 2019 study found that 30 percent of adults who developed type 1 diabetes were initially misdiagnosed with type 2 diabetes (an additional 10 percent were told that they had some other ailment, such as a viral infection). When we asked the Diabetes Daily community for their misdiagnosis stories, we were overwhelmed by the response.

“Type 1 diabetes was called ‘juvenile’ diabetes not too long ago,” Fang says. “I think this idea has become engrained in a lot of people’s minds. The lack of data on the broad age range in which type 1 diabetes can occur has allowed this idea to persist.”

When clinicians fail to identify type 1 diabetes, Fang says, “This can result in acute and long-term complications.”

“If we think a patient has type 2 diabetes, they’re typically treated with oral medications … Insulin is a last-line therapy, so usually you don’t start this medication until A1C levels are above recommended levels and you’ve exhausted other oral medication options … So, there may be a delay in being put on insulin for patients who need it.”

Late Diagnoses for Men and Minorities

The analysis also found that different types of people are diagnosed with type 1 diabetes at different ages:

Men were diagnosed at a later age (median age: 27 years) than women (22 years)
White patients were diagnosed at an earlier age (21 years) than Black (30 years), Hispanic (26 years), and Asian (29 years) patients

Determining the cause of these differences requires more research, Fang says.

“It’s difficult to know the exact reason. It may be related to differences in health care access, in the case of whites versus non-whites, and/or differences in receipt of regular care, in the case of women versus men. Some have also speculated that there may be differences in the age at which different populations are exposed to environmental risk factors that “trigger” the onset of type 1 diabetes.”

Although it’s impossible to know the source of these disparities, this appears to be yet another element of the regrettable equality problem in the American diabetes community.

Raising Awareness

Fang hopes that his team’s work will help shine a light on the issue of misdiagnosis.

“Guidelines currently recommend that providers test for autoantibodies when they suspect an adult patient ‘may’ have type 1 diabetes. I suspect this isn’t performed very often, partly because of the lack of awareness that type 1 diabetes can occur in adults.”

“Until this study,” Fang says, “we didn’t have national data on the age of diagnosis … as a result, people relied on prior knowledge (e.g., that type 1 diabetes is a ‘childhood’ disease).”

Fang is also hopeful that future research will help make it easier to distinguish between types 1 and 2. Clinicians today still rely on old stereotypes in deciding when to order autoantibody testing: “age at diagnosis and body-mass index (with T1DM adults typically being younger and leaner).” Giving everyone with type 2 diabetes an autoantibody panel, however, would likely only result in false positives and misdiagnoses in the opposite direction.

In the future, clinicians may be able to use more sophisticated screening techniques, Fang says: “People in precision medicine are actively trying to find different genetic markers that might help improve classification.”

Fang, et al. Age at Diagnosis in U.S. Adults With Type 1 Diabetes. Annals of Internal MedicineSeptember 26, 2023.

Muñoz, Cynthia et al. Misdiagnosis and Diabetic Ketoacidosis at Diagnosis of Type 1 Diabetes: Patient and Caregiver Perspectives. Clinical Diabetes. July, 2019.

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