Even Mild COVID-19 Infections Increase Risk of Type 2 Diabetes, Research Shows

The new study is the first to look at the relationship between mild infections and diabetes.

Covid Virus inside of Blood Glucose Meter with testing sticks on a blue background
Photo: Design by Jo Imperio

Even a mild COVID-19 infection may increase your chances of developing type 2 diabetes, new research shows. The findings suggest that diabetes screening—even in patients without severe disease—may be warranted.

The study, published in the journal Diabetologia, found that adults who recover from a mostly mild case of COVID-19 may have a higher risk of receiving a new diabetes diagnosis. Though previous studies have linked a severe COVID-19 infection with the onset of type 2 diabetes, the new report is the first to link mild illness with the condition.

"COVID-19 may lead to diabetes," Wolfgang Rathmann, MD, MSPH, deputy director for the Institute for Biometrics and Epidemiology and lead study author, said in a press release. "If confirmed, these results indicate that diabetes screening in individuals after recovery from mild forms of COVID-19 should be recommended," the press release said.

Below, what to know about how COVID-19 influences type 2 diabetes risk, according to the new report.

Mild COVID-19 and New Type 2 Diabetes Diagnoses

Researchers have been studying how diabetes and COVID-19 are related throughout the pandemic, and a Centers for Disease Control and Prevention (CDC) report published in January suggests COVID-19 patients are at a higher risk for receiving a diabetes diagnosis in the 30 days after an infection.

The authors behind the new Diabetologia report wanted to determine whether COVID-19 caused diabetes only in patients who experienced severe illness. "The problem is that most of the studies are based on hospital records so they comprise severe cases. And we were interested in mild cases of COVID-19," Dr. Rathmann told Health.com, noting that most COVID-19 cases are mild.

From March 2020 to January 2021, researchers analyzed medical records from 1,171 doctors' offices in Germany where there were 35,865 patients with mild COVID-19 infection. A separate group of patients with acute upper respiratory tract infections not caused by COVID-19 served as the researchers' control group.

Because research has found that corticosteroids can cause insulin resistance and increase the risk of diabetes, the researchers excluded patients taking corticosteroids. Additionally, the team excluded patients who already had diabetes.

The team followed up with both the control group and the COVID-19 patients between four and 16 months after recovery, and their results showed that people with COVID-19 were more likely to develop type 2 diabetes compared to those in the control group. Specifically, for every 1,000 COVID-19 patients, about 15.8 developed diabetes; that number for the control group was only 12.3.

Dr. Rathmann noted that his team didn't look into why even patients with mild COVID-19 were more likely to develop diabetes. However, he speculated that SARS-CoV-2 (the virus that causes COVID-19 infection) may directly cause diabetes by prolonging the body's immune and inflammatory response.

In the case of diabetes, one theory is that COVID-19 infection triggers an inflammatory response that damages pancreatic cells involved in regulating the body's response to insulin and ultimately causes high blood sugar levels. "The virus itself creates quite a bit of inflammation and it is in fact that burden of inflammation that can cause insulin resistance and push a patient into that sort of over diabetes range," Joshua D. Miller, MD, MPH, medical director of diabetes care at Stony Brook Medicine, told Health.com.

Diabetes From COVID-19 Infection May Be Temporary

According to researchers from the Diabetologia study, one of the questions yet to be answered from COVID-19 diabetes research is whether post-COVID diabetes can be reversed, or if it's somehow temporary.

Post-COVID diabetes' permanence has been the discussion of other recent research, as well. An April study published in the Journal of Diabetes and its Complications found that almost half of patients who developed diabetes after a COVID-19 infection eventually returned to a healthy or prediabetic state.

From March to September 2020, the researchers reviewed the medical records of 1,902 hospitalized patients with confirmed COVID-19 infection. About 31.2% admitted to the hospital had already been diagnosed with diabetes. Another 13% with no history of the condition were later diagnosed with it (but more than a third of those patients were prediabetic before hospitalization).

Patients diagnosed with diabetes after a COVID-19 infection were more likely to stay in the hospital longer, to have suffered from severe disease, and to have required hospitalization in the intensive care unit (ICU), specifically. These patients were more likely to be younger than people with pre-existing diabetes (54 years old vs. 64 years old) and non-white

The researchers continued to monitor the patients through July 2021, and they found that in 40.6%, blood sugar returned to normal (or became prediabetic), in the aftermath of the diabetes diagnosis. Only 8% of patients still needed insulin to control blood sugar levels a year after hospitalization.

Given that many patients who had newly diagnosed diabetes were prediabetic before COVID-19 infection, the research team suggested that SARS-CoV-2 may have an indirect effect on the body by pushing patients with prediabetes into diabetes. They also noted that the high inflammatory markers observed in people with newly diagnosed diabetes supported the theory that inflammation helps in driving diabetes during infection.

This doesn't necessarily mean that a patient's diabetic symptoms will definitely resolve on their own after a COVID-19 infection, Dr. Miller said, adding that there are still many unknowns about the relationship between the two conditions.

Monitoring Blood Sugar Levels After COVID-19 Recovery

While the science points to a link between COVID-19 and diabetes, both Dr. Miller and Dr. Rathmann said most people who recover from COVID-19 infection will not develop disease.

Moreover, Dr. Miller said the results of the studies should not alarm people to constantly check their blood sugar levels at home. Instead, he recommended that patients ask their doctor to check their blood sugar levels during regular check-ups after a COVID-19 infection.

"Oftentimes, the doctor will check some blood levels periodically when they're doing commercial lab testing, but rarely do we recommend the patient routinely check blood sugars [levels] unless something in their blood raises their doctor's concern for developing type 2 diabetes or prediabetes," Dr. Miller said.

He added that the best way to lower your risk of (or even delay the onset of) diabetes is to get enough exercise: "If you have a family history of diabetes, if you smoke cigarettes, if you're sedentary, if you're overweight or obese, all of that risk is just exponentially heightened."

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