In a recent study posted to the medRxiv* preprint server, researchers assessed the association between diabetes mellitus (type 2 diabetes) and mortality among patients hospitalized with coronavirus disease 2019 (COVID-19) at multiple centers in Canada and Denmark.

Studies have reported higher death risks among COVID-19 patients with a history of diabetes; however, detailed analyses on the association between the severity of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections and the presence of comorbid conditions are lacking. Moreover, previous studies that described the association between diabetes and the risk of COVID-19 deaths were conducted at single centers with analysis of regional data of patients with varying COVID-19 severity.

Study: The association between diabetes and mortality among patients hospitalized with COVID-19: Cohort Study of Hospitalized Adults in Ontario, Canada and Copenhagen, Denmark. Image Credit: Design_Cells / ShutterstockStudy: The association between diabetes and mortality among patients hospitalized with COVID-19: Cohort Study of Hospitalized Adults in Ontario, Canada and Copenhagen, Denmark. Image Credit: Design_Cells / Shutterstock

About the study

In the present study, researchers assessed the association between diabetes and death among hospitalized COVID-19 individuals residing in Ontario and Copenhagen.

The study cohort comprised individuals aged >18 years who were hospitalized due to COVID-19 between 1 January 2020 and 30 November 2020 in Ontario (n=1,018) and Copenhagen (n=305). Patients admitted to 10 hospitals in Ontario were retrospectively analyzed and those admitted to eight hospitals in Copenhagen were prospectively analyzed.

Data were primarily obtained from electronic medical records of patients and secondarily obtained manually. Patients hospitalized due to COVID-19 were identified at departments of infection prevention and control of the hospitals and via central repository data comprising COVID-19 laboratory test reports.

Data were obtained on demographical parameters (sex, age, proficiency in English, and residential location before hospital admission) and medical history (including cardiovascular diseases, pulmonary diseases, smoking habits, and kidney failure). Data of medication use, within-hospital laboratory tests [completed blood count (CBC), C-reactive protein (CRP), D-dimer, and troponin], imaging [chest x-rays (CXR), computed tomography (CT) chest, echocardiography (ECG), and doppler ultrasound (USG)] were also obtained.

Diabetic patients were identified by hemoglobin (Hb)A1C values greater than 6.5, current usage of ≥1 injectable or oral diabetic medication, or chart reviews of individuals with physician notes mentioning diabetes. The primary study outcome was 30-day death risks within hospitals, and proxy markers for COVID-19 severity included were CRP, creatinine, troponin, D-dimer, abnormal CXR findings, and oxygen supplementation requirements.

Chart abstraction analyses and Poisson regression modeling was used to determine the association between COVID-19 severity and comorbidities. The crude mortality rate ratio and the adjusted Poisson regression model values were calculated for both nations, and subsequently, a meta-analysis was performed to obtain composite values.


A total of 1,438 patients hospitalized due to COVID-19 were analyzed, of which 78.8% (n=1,133) and 21% (n=305) resided in Ontario and Denmark, respectively. Among the study participants, 33% were diabetic, comprising 405 Ontario residents and 75 Denmark residents. Diabetic individuals had an increased likelihood of being elder and having chronic renal diseases, cardiovascular diseases, elevated troponin levels, and antibiotic medication use than non-diabetics. COVID-19 hospitalized patients with a history of diabetes tended to have more severe COVID-19 (e.g., elevated CRP levels, worse CXR findings) and worse prognosis in Canada and Denmark.

In Ontario, the adjusted regression model and crude mortality rate ratio for diabetic COVID-19 patients were 1.2 and 1.6, respectively. The corresponding values for Denmark-residing diabetic COVID-19 patients were 0.87 and 1.27, respectively. The meta-analyzed values for both nations resulted in corresponding values of 1.11 and 1.55, respectively.  

To conclude, based on the study findings, the risk of in-hospital COVID mortality was not significantly higher among diabetics compared to non-diabetics. However, it is not known whether a diabetic presented with more severe illness due to delayed seeking of appropriate care leading to potential bias in case selection. Further, factors with potential influence on COVID-19 severity, such as ethnicity and socioeconomic status, could cause confounding bias and therefore, further research must be conducted considering such factors.

Study limitations

The HbA1C values were not available for all the study participants, and therefore, COVID-19 severity could not be assessed for the entire study cohort. Further, for the diabetic individuals, type of diabetes viz. types 1 and 2 was not identified. Data on important health determinants such as race, educational status, income, and comorbidities such as obesity [elevated body mass index (BMI)] were lacking. 

Therefore, the association found between diabetes and COVID-19-associated in-hospital deaths could have been overestimated in the present study. Both nations selected for the study were high-income nations with the presence of socialized health systems and therefore, the study findings may have low generalizability.

*Important notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Journal reference:

  • The association between diabetes and mortality among patients hospitalized with COVID-19: Cohort Study of Hospitalized Adults in Ontario, Canada and Copenhagen, Denmark. Orly Bogler, MD, Afsaneh Raissi, Michael Colacci, MD, Andrea Beaman BScPhm, PharmD, RPh , Tor Biering-Sørensen MD, PhD, MPH, Alex Cressman, MD, MSc, Allan Detsky, MD, PhD, Alexi Gosset, BA, Mats Højbjerg Lassen, MD , Chris Kandel, MD, PhD, Yaariv Khaykin, MD David Barbosa, Lauren Lapointe Shaw, MD, PhD, Derek R. MacFadden, MD, ScD, Alexander Pearson, MD, Bruce Perkins, MD, MPH, BSc, Kenneth J. Rothman, DrPH, Kristoffer Grundtvig Skaarup, MD, Rachael Weagle, MD, MPH, Chris Yarnell, MD, Michelle Sholzberg, MDCM, MSc, Bena Hodzic-Santor MD Candidate, Erik Lovblom, Jonathan Zipursky, MD, Kieran L. Quinn, MD, PhD, and Mike Fralick, MD, SM, PhD. medRxiv preprint 2022, DOI: https://doi.org/10.1101/2022.07.04.22276207, https://www.medrxiv.org/content/10.1101/2022.07.04.22276207v1


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