Adult-Onset Type 1 Diabetes Is More Common Than You Think
When many people think of type 1 diabetes, they picture children. But new research published in Diabetes Care, a journal of the American Diabetes Association, reminds us that more than half of new type 1 diabetes cases occur in adults.
Adult-onset type 1 diabetes is far more common than many people realize. Unfortunately, adults are also more likely to be misdiagnosed with type 2 diabetes, which can delay appropriate insulin treatment and increase the risk of complications.
So, what else did the study find, and why does it matter for clinicians, as well as friends and family of people living with or at risk for type 1 diabetes?
What Are Some of the Key Findings From the Research?
Researchers at the Barbara Davis Center compared more than 400 adults with newly diagnosed type 1 diabetes with 2,000 children and adolescents. Here are their key observations about how type 1 diabetes can present differently depending on age at diagnosis—and why those differences matter.
Adults were far less likely to present with diabetic ketoacidosis than children.
In fact, only about 33% of adults presented with diabetic ketoacidosis (DKA), compared with 56% of children and adolescents. Among adults diagnosed after age 40, that number dropped to only about 14%. In other words, DKA seems to become progressively less common the older someone is when they are diagnosed.
Why Does This Matter?
DKA is a serious, potentially life-threatening complication of diabetes. It can be physically distressing, frightening, and traumatic, especially when it is someone’s first experience with diabetes. Earlier recognition of type 1 diabetes symptoms and timely treatment may help prevent DKA and the additional health risks that come with it.
Adults had a slightly lower average A1C at diagnosis than children.
Though still quite high, adults had a slightly lower average A1C at diagnosis: 11.3%, compared with 12.0% in children. Among adults over age 40, the average A1C was 10.3%. However, keep in mind that all of these averages indicate substantial hyperglycemia at diagnosis.
Like the frequency of DKA, average A1C also decreased progressively across the adult age groups, from 11.8% among adults ages 20 to 30, to 11.2% among those ages 30 to 40, and 10.3% among those over age 40.
Why Does This Matter?
Researchers interpreted this as evidence that adult-onset T1D, particularly later in adulthood, can have a less acute clinical presentation. In other words, an adult can still have serious insulin deficiency and type 1 diabetes even with a somewhat lower A1C and without being in DKA.
This less dramatic presentation may contribute to a missed or delayed diagnosis because clinicians may expect adult-onset T1D to look more like the acute presentation commonly seen in children.
Adults with newly diagnosed type 1 diabetes frequently had a less obvious islet autoantibody profile.
Adults were more likely to have only one, or even no detectable islet autoantibodies, despite having type 1 diabetes. Only 57% of adults had multiple antibodies, compared with about 80% of children. In contrast, 15.9% had none of the four measured antibodies, versus 6.6% of children.
GAD antibodies were the most useful single marker in adults. GADA was present in about 75% of adults, while insulin, IA-2, and ZnT8 antibodies were substantially less common than in children.
Why Does This Matter?
This matters because relying too heavily on autoantibody results could cause adult-onset T1D to be missed or mistaken for type 2 diabetes. Although autoantibody testing remains important, a negative result does not automatically rule out T1D.
Clinicians may also need to consider other measures, including C-peptide levels, insulin dependence, DKA, BMI, and the person’s overall clinical presentation. Which, brings us to our final consideration…
Body size was not a reliable way to classify diabetes.
Let me say this a little louder so the clinicians, influencers, and family members in the back can hear: Body size is not a reliable way to classify diabetes. The adults in this study had an average BMI of 23.5, but some were overweight or had obesity. Having a higher BMI does not rule out type 1 diabetes.
Why Does This Matter?
The clinical significance of this should go without saying. Using BMI to diagnose or classify diabetes can lead to someone’s true clinical etiology being grossly misinterpreted.
That misclassification may affect their treatment, prognosis, expected disease progression, and understanding of their personal risk factors. It may also prevent biological family members from recognizing their own increased risk.
Type 1 diabetes is not directly inherited in a simple pattern, but biological relatives of someone with autoimmune T1D may have a higher risk of developing the condition.
What Healthcare Professionals Should Take Away From This Research
As a healthcare professional, if there is one thing you take away from this research, let it be that age, BMI, the absence of DKA, or a negative autoantibody result alone is not a reliable way to distinguish type 1 from type 2 diabetes.
Adult-onset T1D may develop more gradually, so diagnosis should consider the whole clinical picture, including symptoms, ketones, insulin requirements, C-peptide interpreted with a concurrent glucose level, a complete autoantibody panel, autoimmune history, and response to treatment.
What Friends and Family Members Should Take Away From This Research
Type 1 diabetes can develop at any age. Watch for excessive thirst, frequent urination, unexplained weight loss, fatigue, blurry vision, increased hunger, and recurrent infections. Nausea, vomiting, abdominal pain, rapid breathing, fruity-smelling breath, or confusion may indicate DKA and require urgent medical attention.
If someone has symptoms, ask, “Could this be type 1 diabetes, even though they are an adult?” Older age, a higher body weight, an initial type 2 diagnosis, or the absence of DKA does not rule out T1D. Family history can increase risk, but most importantly, its absence does not mean someone is not at risk.
Frequently Asked Questions About Adult-Onset Type 1 Diabetes
Yes. Type 1 diabetes can develop at any age, including after age 40. Adult-onset type 1 diabetes is more common than many people realize and is sometimes misdiagnosed as type 2 diabetes.
Common symptoms include excessive thirst, frequent urination, unexplained weight loss, fatigue, blurry vision, increased hunger, and recurrent infections. Nausea, vomiting, abdominal pain, rapid breathing, fruity-smelling breath, or confusion may indicate diabetic ketoacidosis and require urgent medical attention.
Adult-onset type 1 diabetes may develop more gradually and appear less acute than it does in children. An adult’s age, body size, lack of DKA, or less obvious autoantibody results may lead healthcare professionals to initially suspect type 2 diabetes.
Yes. An adult does not need to be in diabetic ketoacidosis or appear critically ill to have type 1 diabetes. In this study, about 33% of adults presented with DKA, compared with 56% of children and adolescents.
Yes. Type 1 diabetes can develop after age 40 and even much later in adulthood. Among adults over age 40 in this study, only about 14% presented with DKA, showing that later-onset T1D may have a less acute presentation.
Yes. Some adults with clinically diagnosed type 1 diabetes may test negative for the commonly measured islet autoantibodies. A negative result does not automatically rule out T1D, but it should lead to a careful review of the person’s complete clinical presentation and other possible diagnoses.
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