Nearly 4 in 10 Adults with T1D Diagnosed After Age 30 Years, Study Finds

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Type 1 diabetes was diagnosed later for men than women and for racial and ethnic minority adults than non-Hispanic White adults.

A new analysis investigating the age distribution of type 1 diabetes (T1D) diagnosis in the United States found approximately 4 in 10 adults were diagnosed after age 30 years.1

Collecting data on 947 adults with T1D from the National Health Interview Survey, representing approximately 1.3 million adults in the US, investigators found both men and racial and ethnic minorities had a substantially higher age at diagnosis.

“Consistent with our findings, prior studies suggest that more than half of T1D cases develop in adults,” wrote the investigative team, led by Elizabeth Selvin, PhD, MPH, Johns Hopkins Bloomberg School of Public Health. “We extended existing research by characterizing the age at diagnosis in a nationally representative sample and by documenting variation across race/ethnicity and clinical characteristics.”

New-onset T1D in adulthood is often taken for type 2 diabetes, due to the presentation of mild symptoms, and can lead to improper care. Selvin and colleagues point to new evidence suggesting that up to 62% of T2D cases develop after 20 years of age, but most studies are performed in selected clinical populations.2 They note an improved understanding of the burden of adult-onset T1D in the general population could help reduce misdiagnosis.1

Based on this assumption, the investigative team aimed to characterize the age distribution of T1D diagnosis in the United States, both overall, and according to demographic and clinical characteristics. Using the National Health Interview Survey, investigators combined all survey cycles for which diabetes subtype data were available: 2016, 2017, 2019, 2020, 2021, and 2022.

Demographic and clinical characteristics, including a history of diabetes, were collected through interviews. Those with diabetes reported the disease type, use of insulin, and age at diagnosis. The analysis included adults aged 18 years and older with T1D, defined in the analysis as a reported diagnosis of T1D and current use of insulin.

For analysis, investigators estimated the median age at diagnosis and the percentage of adults who were diagnosed after age 20, 30, and 40 years, overall, and by demographic and clinical characteristics. A total of 947 adults with T1D in NHIS cycles between 2016 to 2022 were included in the analysis, representing approximately 1.3 million adults in the US. The mean age at the time of the survey was 49 years; 48% were women and 73% were non-Hispanic White.

The analysis showed the median age at diagnosis was 24 years old. Investigators found T1D was diagnosed later for men compared with women (median age, 27 years vs. 22 years) and for racial and ethnic minority adults compared with non-Hispanic White adults (median age, 26 to 30 years vs. 21 years). Overall, data showed that 37% of participants had a diagnosis after the age of 30 years, with higher rates for men and racial and ethnic minorities.

Selvin and colleagues noted it remains unclear how to best identify adults with high risk of T1D. Traditional biomarkers used to differentiate T1D and T2D may have limited utility, including body mass index, due to the ubiquity of obesity in patients with T1D. As a result, the investigative team suggests novel risk scores combining clinical features and relevant biomarkers could improve diagnosis.

“Tools integrating clinical measures and biomarkers may improve the accuracy of diagnosis for these patients,” investigators wrote.


  1. Fang M, Wang D, Echouffo-Tcheugui JB, Selvin E. Age at Diagnosis in U.S. Adults With Type 1 Diabetes [published online ahead of print, 2023 Sep 26]. Ann Intern Med. 2023;10.7326/M23-1707. doi:10.7326/M23-1707
  2. Gregory GA, Robinson TI, Linklater SE, et al; International Diabetes Federation Diabetes Atlas Type 1 Diabetes in Adults Special Interest Group. Global incidence, prevalence, and mortality of type 1 diabetes in 2021 with projection to 2040: a modelling study. Lancet Diabetes Endocrinol. 2022;10:741-760. [PMID: 36113507] doi:10.1016/S2213- 8587(22)00218-2