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Researchers say people who experienced severe COVID-19 should be monitored for signs of diabetes, and clinicians should use their discretion to monitor anyone else who has been infected, based on other risk factors for diabetes such as obesity.Fred Lum/the Globe and Mail

With COVID-19 activity beginning to rise again heading into the fall, U.S. cardiologist Alan Kwan says it’s still important for people to try to avoid infection, as he and other scientists continue to try to understand the lasting repercussions of the disease.

Among other potential long-term effects, researchers around the world are seeking to unravel the relationship between COVID-19 and diabetes, a condition that impairs the body’s ability to control and use sugar in the blood and raises the risk of other complications including blindness, heart attacks and kidney failure. Even though the mechanisms are still unclear, growing evidence suggests more people are developing diabetes after catching COVID-19.

In a study published earlier this year in the journal JAMA Network Open, Dr. Kwan and his colleagues found a significant increase in people’s risk of developing diabetes after an infection. That risk persisted after the emergence of the Omicron variant, they found, and while their data strongly suggested that vaccinations were protective against the risk of subsequent diabetes, Dr. Kwan said this was not conclusive.

“The potential effects of a COVID infection are likely different than other viral infections that we’re used to, seasonal colds, even flus, stuff like that,” said Dr. Kwan, the lead author of the study at Cedars-Sinai Medical Centre in Los Angeles. “And so, in the space of uncertainty, really protecting yourself against infection is very important.”

Canada needs a long-COVID strategy

The heightened risk for individuals appears to be small. But on a population level, a bump in diabetes cases could add pressure to an already stretched health care system, said Naveed Janjua, executive director of data and analytic services at the BC Centre for Disease Control.

In a separate study, also published in JAMA Network Open earlier this year, Dr. Janjua and his team analyzed the health data of nearly 630,000 adults in British Columbia, comparing those who tested positive for COVID-19 with those who tested negative. The researchers assessed whether they were diagnosed with diabetes more than 30 days after infection.

They found the risk of diabetes was about 17 per cent to 22 per cent higher among those who had tested positive for COVID-19. Men had slightly higher risk than women, and people who had more severe illness, including those who were admitted to hospital or required intensive care, were also at higher risk.

The researchers estimated this translated to a three-per-cent to five-per-cent excess burden of diabetes between January, 2022, and January, 2023, a period when Omicron subvariants were dominant and most Canadians had already received their primary series of vaccines. In other words, among every 100 new cases of diabetes, up to five could be related to COVID-19, Dr. Janjua explained.

People who experienced severe COVID-19 should be monitored for signs of diabetes, and clinicians should use their discretion to monitor anyone else who has been infected, based on other risk factors for diabetes such as obesity, Dr. Janjua said.

There are different types of diabetes. The most common are Type 2, where the body doesn’t respond normally to insulin, and Type 1, where the pancreas doesn’t make enough insulin.

Dr. Janjua said his study primarily looked at Type 2 diabetes. Dr. Kwan’s research did not parse out the type. But other studies have shown COVID-19 is associated with increases in both types of diabetes in children and adults.

For Type 1 diabetes, it may be possible that the virus causes some degree of damage to the pancreas, Dr. Kwan explained, but he believed this was unlikely to be driving the rise in Type 2 diabetes diagnoses.

The COVID-19 response in Canada: what if there is no inquiry?

Since inflammation can affect the body’s ability to handle blood sugar and respond to insulin, it’s possible that COVID-19 can tip the scales for people who were already predisposed or on the verge of becoming diabetic, Dr. Kwan said. Other hypotheses involve some aspects of autoimmunity related to chronic inflammation after a COVID-19 infection, or steroid medications, like dexamethasone, used to treat patients in hospital with COVID-19, which may affect the way they handle blood sugar, Dr. Kwan added.

Dr. Janjua emphasized more research is needed to determine whether the diabetes people develop after COVID-19 persists or goes away with time.

Early in the pandemic, fears that there was a rash of new diabetes cases related to COVID-19 was “actually a little overblown,” said Sara Cromer, an assistant in medicine at Massachusetts General Hospital and instructor at Harvard Medical School. Her research found many people who had what looked like evidence of diabetes while sick in hospital with COVID-19 early in the pandemic actually recovered and did not have diabetes in the long-term.

It’s common for people to have high blood sugar when they are very sick and under stress because of certain stress hormones, Dr. Cromer said, explaining the phenomenon is not unique to COVID-19.

She pointed out, however, that further studies have shown even mild cases of COVID-19 may be associated with developing diabetes months later.

Dr. Cromer said she encouraged people to stay up to date with the recommended vaccines this fall.

Meanwhile, Dr. Kwan emphasized the need to continue to pay attention to COVID-19 and the underserved populations it has disproportionately affected.

“We’re all very tired of COVID, but it does remain a significant issue,” he said.

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