Scientists around the world noticed an uptick in new diabetes cases last year and, in particular, saw that some COVID-19 patients with no history of diabetes were suddenly developing the condition, Scientific American reported. The trend prompted many research groups to launch studies of the phenomenon; for instance, researchers at King's College London in England and Monash University in Australia established the CoviDiab Registry, a resource where doctors can submit reports about patients with a confirmed history of COVID-19 and newly diagnosed diabetes.
More than 350 clinicians have submitted reports to the registry, The Guardian reported. They've reported both type 1 diabetes, in which the body attacks the cells in the pancreas that produce insulin, and type 2 diabetes, in which the body still produces some insulin, though often not enough, and its cells don't respond properly to the hormone.
"Over the last few months, we've seen more cases of patients that had either developed diabetes during the COVID-19 experience or shortly after that," Dr. Francesco Rubino, a professor and chair of metabolic and bariatric surgery at King's College London, told The Guardian. "We are now starting to think the link is probably true — there is an ability of the virus to cause a malfunctioning of sugar metabolism."
Other studies have found a link between COVID-19 and diabetes.
For example, a review of eight studies, which included more than 3,700 hospitalized COVID-19 patients, showed that roughly 14% of these patients developed diabetes, Scientific American reported. A preliminary study of 47,000 U.K. patients found that 4.9% developed diabetes, The Guardian reported.
"We clearly see people without previous diabetes developing diabetes," Dr. Remi Rabasa-Lhoret, a physician and metabolic diseases researcher with the Montreal Clinical Research Institute, told CTV News. "It is highly probable that COVID-19 is triggering the disease."
The big question is why, and scientists have several theories.
It may be that SARS-CoV-2, the virus that causes COVID-19, directly attacks insulin-producing cells in the pancreas, Scientific American reported. Alternatively, the virus may damage these cells indirectly by infecting other parts of the pancreas or the blood vessels that supply the organ with oxygen and nutrients. Still another theory suggests that the virus infects other organs involved with blood sugar regulation, such as the intestines, and somehow undermines the body's ability to break down glucose, more generally.
Other types of viruses — such as certain enteroviruses, which cause various conditions, including hand, foot, and mouth disease — have been linked to diabetes in the past, The Guardian reported. In addition, a subset of patients who caught the coronavirus SARS-CoV, which caused outbreaks of severe acute respiratory syndrome in the early 2000s, also developed diabetes afterward, Dr. Mihail Zilbermint, an endocrinologist and associate professor at the Johns Hopkins School of Medicine, told CTV News.
In general, acute viral infections can spark severe inflammation in the body, and in response, the body produces stress-related hormones, such as cortisol, to tamp down that inflammation. Stress hormones can cause blood sugar levels to spike, and that rise doesn't always subside after the infection clears, Scientific American reported.
In addition, COVID-19 patients are often treated with steroid medications, such as dexamethasone, which can also drive up blood sugar levels. Therefore, it's possible that these steroids also contribute to the onset of diabetes in COVID-19 patients, Zilbermint told CTV News. Steroid-induced diabetes may subside after the patient stops taking the drugs, but sometimes, the condition becomes chronic, according to Diabetes.co.uk.
Another factor contributing to uncertainty about the link, however, is how many of the patients already had prediabetes, meaning they have higher-than-average blood sugar levels, when they caught COVID-19. "It's possible that [a] patient lives with prediabetes for many years and didn't know that," Zilbermint told CTV News. "Now they have COVID-19 infection, and the infection is pushing them towards developing diabetes."
Scientists aren't sure whether the people who developed diabetes after getting COVID-19 will have the condition permanently, Rabasa-Lhoret told CTV News. In at least some patients who developed diabetes after a SARS infection, their diabetic symptoms eventually subsided and their blood sugar returned to normal levels after the infection, according to a 2010 report in the journal Acta Diabetologica. Patients infected with SARS-CoV-2 may experience similar, short-lived diabetic symptoms, but this will need to be confirmed with further studies.