At 18 Months, Much Still Unknown About Diabetes and COVID-19

Miriam E. Tucker

September 13, 2021

At 18 months into the COVID-19 pandemic, many of the direct and indirect effects of SARS-CoV-2 on people with diabetes have become clearer, but knowledge gaps remain, say epidemiologists.

"COVID-19 has had a devastating effect on the population with diabetes, and conversely, the high prevalence of diabetes and uncontrolled diabetes has exacerbated the problem," Edward W. Gregg, PhD, Imperial College London, United Kingdom, lead author of a new literature review, told Medscape Medical News.

"As it becomes clear that the COVID-19 pandemic will be with us in different forms for the foreseeable future, the emphasis for people with diabetes needs to be continued primary care, glycemic management, and vaccination to reduce the long-term impact of COVID-19 in this population," he added.

In data, mostly from case series, the review shows that more than one third of people hospitalized with COVID-19 have diabetes. It is published in the September issue of Diabetes Care.

People with diabetes are more than three times as likely to be hospitalized for COVID-19 than those without diabetes, even after adjustment for age, sex, and other underlying conditions. Diabetes also accounts for 30%–40% of severe COVID-19 cases and deaths. Among those with diabetes hospitalized for COVID-19, 21%–43% require intensive care, and the case fatality rate is about 25%.

In one of the few multivariate analyses that examined type 1 and type 2 diabetes separately, conducted in the UK, the odds of in-hospital COVID-19-related deaths compared with people without diabetes were almost three times higher (odds ratio 2.9) for individuals with type 1 diabetes and almost twice as high (OR 1.8) for those with type 2, after adjustment for comorbidities.

The causes of death appear to be a combination of factors specific to the SARS-CoV-2 infection and to diabetes-related factors, Gregg told Medscape.

"Much of the increased risk is due to the fact that people with diabetes have more comorbid factors, but there are many other mechanisms that appear to further increase risk, including the inflammatory and immune responses of people with diabetes, and hyperglycemia appears to have an exacerbating effect by itself."

Elevated Glucose Is Clear Risk Factor for COVID-19 Severity

Elevated A1c was identified among several other overall predictors of poor COVID-19 outcomes, including obesity as well as comorbid kidney and cardiovascular disease.

High blood glucose levels at the time of admission in people with previously diagnosed or undiagnosed diabetes emerged as a clear predictor of worse outcomes. For example, among 605 people hospitalized with COVID-19 in China, those with fasting plasma glucose 6.1-6.9 mmol/L (110-125 mg/dL) and ≥7 mmol/L (126 mg/dL) had odds ratios of poor outcomes within 28 days of 2.6 and 4.0 compared with FPG <6.1 mmol/L (110 mg/dL).

Population-based studies in the UK found that A1c levels measured months before COVID-19 hospitalization were associated with risk for intensive care unit admission and/or death, particularly among those with type 1 diabetes. Overall, the death rate was 36% higher for those with A1c of 9%–9.9% vs 6.5%–7%.

Despite the link between high A1c and death, there is as yet no clear evidence that normalizing blood glucose levels minimizes COVID-19 severity, Gregg said.

"There are data that suggest poor glycemic control is associated with higher risk of poor outcomes. This is indirect evidence that managing blood sugar will help, but more direct evidence is needed."

Evidence Gaps Identified

Gregg and co-authors Marisa Sophiea, PhD, MSc, and Misghina Weldegiorgis, PhD, BSc, also from Imperial College London, identify three areas in which more data are needed.

First, more information is needed to determine whether exposure, infection, and hospitalization risks differ by diabetes status, and how those factors affect outcomes. The same studies would also be important to identify how factors such as behavior, masking and lockdown policies, risk factor control, and household/community environments affect risk in people with diabetes.

Second, studies are needed to better understand indirect effects of the pandemic, such as care and management factors. Some of these, such as the advent of tele-health, may turn out to be beneficial in the long run, they note.

Finally, the pandemic has "brought a wealth of natural experiments," such as how vaccination programs and other interventions are affecting people with diabetes specifically. Finally, population studies are needed in many parts of the world beyond the US and the UK, where most of that work has been done thus far.

"Many of the most important unanswered questions lie in the potential indirect and long-term impact of the pandemic that require population-based studies," Gregg said. "Most of our knowledge so far is from case series, which only assess patients from the time of hospitalization."

Indeed, very little data are available for people with diabetes who get COVID-19 but are not hospitalized, so it's not known whether they have a longer duration of illness or are at greater risk for "long COVID" than those without diabetes who experience COVID-19 at home.

"I have not seen published data on this yet, and it's an important unanswered question," Gregg said.  

The authors have disclosed no relevant financial relationships.

Diabetes Care. Published September 2021 issue. Full text

Miriam E. Tucker is a freelance journalist based in the Washington DC area. She is a regular contributor to Medscape, with other work appearing in the Washington Post, NPR's Shots blog, and Diabetes Forecast magazine. She is on Twitter @MiriamETucker.

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