People infected with the coronavirus were significantly more likely to be diagnosed with Type 2 diabetes within a year of their infection, compared with those who had not been exposed to the virus, researchers in Canada reported Tuesday.
Men were more likely to develop diabetes than women, the scientists found. People who were so sick that they were hospitalized were more than twice as likely to go on to a diabetes diagnosis, compared with those who were not infected.
People who were admitted to intensive care were more than three times as likely to develop diabetes, the researchers also found. The findings add to a growing body of evidence about COVID's long-term effects.
"This is definitely a concern in terms of long-term outcomes," said Dr. Naveed Z. Janjua, the paper's senior author and a professor at the School of Population and Public Health at University of British Columbia.
"With a respiratory infection, you usually think, 'Seven or eight days, and I'm done with it; that's it,'" he added. "Here we're seeing lingering effects that are lifelong."
The study, published in JAMA Network Open, used a large data set from British Columbia to compare diabetes diagnoses among more than 125,000 individuals who had tested positive for COVID in 2020 and 2021 with those of more than 500,000 unexposed individuals during the same period.
COVID vaccines became available in December 2020, and a majority of participants in both the exposed and unexposed groups had not been fully vaccinated.
More than a dozen studies have looked at the link between COVID and diabetes, and a majority have reported an increase in diagnosis following infection, as well as higher risks for men and those with severe disease.
The findings do not prove that the infection causes diabetes, however. Experts said it was possible, for instance, that patients recovering from COVID were more likely to be diagnosed with diabetes simply because they were receiving more regular care.
Still, there are plausible biological explanations for a link between the two conditions, said Dr. Pamela Davis, a professor of medicine at Case Western Reserve University in Cleveland, who co-wrote a commentary accompanying the study.
"It's reasonable to ask, 'Is this an actual increase, or is this just something that accelerated diabetes that was coming anyway in people, but they got it earlier?'" Davis said in an interview.
"But even if it's just an acceleration, this is going to be costly," she added. "The human suffering, the risk of complications in the eyes, the blood vessels, the heart, the kidneys, the days of productivity and work lost — all those things will be accelerated. I'm worried about this."
The coronavirus infects beta cells in the pancreas that make insulin, Davis said, and cause cell death. These cells are dotted with the ACE2 receptors that the virus uses as an entryway.
"If you put the beta cells of the pancreas in a culture dish, the virus will avidly infect these cells and destroy them," she said.
Stress also plays a role in the development of diabetes, and the inflammatory response that accompanies COVID has been linked to the destruction of beta cells. People with severe COVID may also produce antibodies that attack the patient's own body.
Other viral infections have also been associated with the development of diabetes, according to Janjua, whose research before the pandemic focused on hepatitis.
"With hepatitis C, we have strong evidence that the infection is associated with an increased risk of diabetes as well as cardiovascular outcomes and many other systemic outcomes outside the liver as well," Janjua said.
The new study found that adults who had tested positive for the virus were 17% more likely to develop diabetes within a year of the positive test. Men were 22% more likely to develop diabetes, compared with unexposed individuals. The elevated risk for women was not statistically significant overall unless they were hospitalized or admitted to an intensive care unit.
The researchers matched infected and unexposed people by age and sex and made adjustments to account for differences in underlying health conditions, socioeconomic status, vaccination status and other factors.
They calculated that of all new cases of diabetes, some 3.4% could be attributed to a COVID infection. For men, 4.75% of new cases were attributed to COVID.