3. Acute illness and inflammation are causing symptoms of diabetes. Doctors have known for decades that any severe health event—pneumonia, heart attack, stroke, trauma—can cause blood glucose levels to spike, a condition called hyperglycemia that is a signature of diabetes. Stress-related hormones such as cortisol and adrenaline are believed to cause this elevation, which may subside when the patient recovers or may leave the patient permanently diabetic.

There is no doubt that severe COVID can impose the kind of stress that raises blood glucose in patients who have no history of diabetes, and sends it sky high in those who do.

Endocrinologist Alyson Myers sees this phenomenon daily in her role as medical director of inpatient diabetes at North Shore University Hospital in Manhasset, N.Y. Patients admitted there with COVID, she says, rarely have blood sugar levels in the normal range, which is below 140 milligrams of glucose per deciliter of blood. “They are usually coming in in the 200s,” whether they have a history of diabetes or not, and some arrive in an especially dangerous, hyperglycemic state called diabetic ketoacidosis, more typically seen in type 1 diabetes. “So, it’s not just new-onset, but new-onset of this severe form,” Myers says.

Hyperglycaemia on admission is a predictor of mortality, Myers says, “so you want to get that sugar down as quickly as possible.” It’s not unusual for hospitalized COVID patients to be given very large doses of insulin, even if they never required it in the past.

4. Treating COVID with steroids raises blood sugar. A standard treatment for severe COVID-19 at Myers’ hospital and many others is a combination of the anti-viral drug remdesevir and high doses of a steroid drug such as dexamethasone, which tamps down inflammation. The latter drug, however, raises insulin resistance and may therefore make hyperglycaemia even worse.

This treatment, too, is a reason that COVID patients may suddenly develop severe symptoms of diabetes. “Between the COVID and the steroids, their blood sugar is through the roof,” Myers says, “and we have to give them really high doses of insulin to combat that.”

5. New-onset diabetes might not actually be all that new.  The fact that a patient has no recorded history of diabetes does not mean that they weren’t already diabetic or pre-diabetic or predisposed to the disease by virtue of genetics, obesity or some other factor.

All of these conditions are remarkably common. In the U.S., for example, the Centres for Disease Control and Prevention estimates that 10.5 percent of people have diabetes, one fifth of whom have not yet been diagnosed. Another 34 percent of the adult population has elevated blood sugar in the prediabetic range.

“Diabetes is typically a silent disease for a very long time,” Rubino says. “Estimates are that you may have it for five or more years without knowing it.” 

One way to tell whether silent diabetes was already present in COVID patients, Rubino notes, is with a commonly used blood test called A1C that indicates average blood sugar levels for the previous three months: “A normal A1C allows you to be more confident that there wasn’t any diabetes two or three months ago.” Where available, A1C data will be an illuminating component of the CoviDIAB registry, as will follow-up data showing whether COVID-related diabetes vanishes as suddenly as it arose or if it persists.

Understanding precisely how the coronavirus disrupts glucose metabolism could help resolve longstanding questions about the role other infections play in diabetes. Viruses such as Coxsackie B and rubella are known to be associated with some cases of type 1 diabetes, but small data sets have made it difficult to pin down a mechanism. “With a pandemic we will probably see more cases than we’ve ever seen before,” Rubino says. “That’s why the story of COVID and diabetes is important for the understanding the role of viruses in causing diabetes.”

https://www.scientificamerican.com/article/unraveling-the-complex-link-between-covid-and-diabetes/