By now, it’s an established fact that coronavirus patients who also suffer from diabetes are at a higher risk of death. But what’s perhaps even more worrisome is that COVID-19 might actually trigger the onset of diabetes in previously healthy people, according to new research.

Diabetes is a disease that occurs when your blood glucose, also called blood sugar, is too high. There are two types of diabetes that can lead to this outcome.

Type 1 is triggered when the body’s own immune cells attack the islet cells in the pancreas responsible for producing insulin. This merciless attack is continuously carried out until there are no more islets left, halting the production of the insulin that controls blood glucose levels. As such, Type 1 diabetes is considered an autoimmune disease.

In Type 2 diabetes, insulin is still produced normally by the pancreas, however, the body is still unable to shuttle glucose into cells for fuel. This is due to growing insulin resistance in the body’s organs and tissue, such as in the liver, muscle, or fat. Because the body doesn’t respond to insulin messaging, the islet cells start producing too much insulin, exhausting the islet cells. Eventually, the islet cells start dying, decreasing insulin production while resistance increases.

Although both forms of diabetes have been studied for decades, there are still many unknowns as to how the two diseases are triggered. One possible avenue of disease onset may be viral infection.

For instance, the incidence of Type 1 diabetes often co-occurs with seasonal viral infections, and some claim that viruses can trigger the destruction of the islet cells, triggering a chronic autoimmune response.

In a recent article, Julian Hamilton-Shield, a professor in Diabetes and Metabolic Endocrinology at the University of Bristol, draws attention to a worrisome trend, stating that COVID-19 may trigger diabetes in some patients.

Hamilton-Shield points to the case of a Chinese young man of previous good health who developed severe diabetes after contracting COVID-19. He also mentions how during the SARS outbreak in 2002-2004, many people with SARS pneumonia went on to develop acute diabetes, something which wasn’t seen in patients with other types of pneumonia. SARS is another coronavirus closely related to SARS-CoV-2, the virus responsible for COVID-19. Although diabetes resolved within three years for most patients, it persisted in 10% of cases.

This sentiment is shared by leading experts who recently wrote an open letter published in The New England Journal of Medicine, in which they claim there may be “a bidirectional relationship between Covid-19 and diabetes.”

How COVID-19 might cause diabetes

SARS-CoV-2 infects susceptible cells by binding to angiotensin-converting enzyme 2 (ACE2) receptors. These receptors are expressed in some metabolic organs and tissue, including pancreatic beta cells and the kidneys. This may explain why patients with preexisting diabetes are at greater risk, while also pointing to new mechanisms of disease onset.

However, there are still many unknowns.

“How frequent is the phenomenon of new-onset diabetes, and is it classic type 1 or type 2 diabetes or a new type of diabetes? Do these patients remain at higher risk for diabetes or diabetic ketoacidosis? In patients with preexisting diabetes, does Covid-19 change the underlying pathophysiology and the natural history of the disease? Answering these questions in order to inform the immediate clinical care, follow-up, and monitoring of affected patients is a priority,” wrote the authors of the letter published in The New England Journal of Medicine.

To clear things up, diabetes researchers have launched the CoviDIAB Project, which aims to compile a global registry of COVID-19 patients with new-onset diabetes.

“Given the very short history of human infection with SARS-CoV-2, an understanding of how Covid-19–related diabetes develops, the natural history of this disease, and appropriate management will be helpful,” the authors of the letter concluded.