How COVID-19 and Diabetic Retinopathy Are Linked

There are many factors that may lead someone infected with the coronavirus to suffer severe and potentially fatal outcomes, but the single most common factor linking COVID-19 and death may be diabetes.

Back in August, the U.S. Centers for Disease Control and Prevention analyzed more than 10,000 COVID-related deaths between February and May. The study found that almost 40% of the people who died had diabetes. A study by Reuters found similar results.

This past November, another study conducted in England homed in on one specific complication of diabetes, called diabetic retinopathy. This is a common eye disease among those with diabetes, caused when high blood sugar damages the tiny blood vessels in the retina. This study found that patients with diabetic retinopathy were five times more likely to need intubation when hospitalized with COVID-19 than other patients.

The study was small — just 187 patients hospitalized with severe COVID-19 — but the results are still startling. In a statement release, the study’s first author Dr. Antonella Corcillo, from the School of Cardiovascular Medicine and Sciences at King’s College London, said retinopathy is a marker of damage to the blood vessels, “and our results suggest that such pre-existing damage to blood vessels may result in a more severe COVID-19 infection requiring intensive care treatment.”

Senior author Dr. Janaka Karalliedde, also from King’s College London, added that there is increasing evidence of significant damage to the blood vessels in the lung and other organs in patients hospitalized with severe COVID-19. “People with diabetes are at high risk of vascular complications affecting the large and small blood vessels. We hypothesize that the presence of diabetes-related vascular disease such as retinopathy may result in greater vulnerability and susceptibility to respiratory failure in severe COVID-19,” he said in the statement.

[See: 10 Myths About Diabetes.]

COVID-19 Attacks Blood Vessels

This wasn’t a shock to Chris Hudson, a professor in the school of optometry at the University of Waterloo and in the department of ophthalmology and vision science at the University of Toronto. “I knew this was a virus that singled out and attacked blood vessels. People with diabetes are compromised anyway, so this combination did not surprise me.”

In diabetic retinopathy, high blood sugar breaks down the blood vessels to the point that they begin to leak, becoming less efficient at transporting blood through the retina. “A biochemist friend of mine said it’s like a caramelization that triggers changes in blood vessels and nerves,” Hudson says. “They are so high in glucose, it’s like a slow-cooking mechanism, if you like.”

That same process affects nerves and blood vessels throughout the body, leading to other diabetes complications such as heart disease, kidney disease and neuropathy. “What we see in the eye is reflected in virtually all other organs in the body. It’s just that we can see it easier in the eye,” he says.

[SEE: Coronavirus and Diabetes.]

Correlation Not Causation

One thing to keep in mind: The study in England is correlative, not causative. “It’s an observational study that notes an interesting statistic correlation that gets people thinking,” says Dr. Robert Gabbay, chief scientific and medical officer of the American Diabetes Association. “The question is, what explains that association. Is it telling us something deeper? It’s hard to tell. It’s a correlation that has some potential biology behind it, in theory. That’s what makes it tantalizing.”

On its own, this study doesn’t tease out whether it’s retinopathy or another coexisting condition like obesity, kidney disease or heart disease, that contributes to more severe COVID symptoms, Gabbay says. “We know (diabetes and COVID) is a lethal combination, in part driven by the commonality of having obesity and cardiovascular disease. We also know that’s not the full story,” he says.

For example, a recent study out of Vanderbilt University found that risks from COVID were similar between those with Type 2 diabetes and Type 1 diabetes, which is far less often associated with obesity. Instead, blood sugar control seems to be the crucial factor: Those who have uncontrolled blood sugar levels appear to do worse than those with controlled sugars, Gabbay says.

[See: What Are the Symptoms of Coronavirus?]

A Strong Message

The message to those with diabetes, Gabbay believes, is to be very careful “in the usual ways” — wear a mask, stay socially distant, wash your hands often. Also, be sure to maintain blood sugar control, and perhaps most important, stay in contact with your doctors. “Because COVID has gone on longer, people have deferred their health care, particularly for chronic diseases like diabetes. This is a long time to not be engaged with your health care team,” he says. Telehealth visits are an option for many patients who are reluctant to visit a doctor in person.

Hudson offers another suggestion, now that vaccines are becoming available for the coronavirus: “If you have diabetes, you should push to get the vaccination quickly.”

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How COVID-19 and Diabetic Retinopathy Are Linked originally appeared on

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