A large population-based study from the British Columbia Centre for Disease Control suggests that COVID-19 infection is associated with an increased risk of type 2 diabetes in unvaccinated and severely ill patients, with elevated risk persisting for up to 3 years after infection.
In the study, published in Diabetes/Metabolism Research and Reviews, the team analyzed data from more than 2 million adults who underwent COVID testing from January 2020 to January 2024. The group included 296,390 people who tested positive and 1.7 million who tested negative. Individuals with pre-existing diabetes or those residing in long-term care were excluded from the study.
Over a median follow-up of 874 days, 47,704 participants (2.3%) were diagnosed as having type 2 diabetes. The incidence rate was 11.6 per 1,000 person-years among those with a COVID infection, compared with 9.3 per 1,000 person-years in those who tested negative for COVID, reflecting an 18% higher risk of type 2 diabetes for those who tested positive.
The elevated risk was most pronounced in the first year after infection (hazard ratio [HR], 1.21) and remained significantly increased through years 2 (HR, 1.19) and 3 (HR, 1.17). Beyond 3 years, the association was no longer statistically significant (HR, 1.15).
No risk observed among vaccinated individuals
Risk rose sharply with severity of COVID infection. Compared with individuals who tested negative, those with COVID who were managed in ambulatory care had a 15% increased risk (HR, 1.15) of type 2 diabetes, hospitalized patients had nearly double the risk (HR, 1.98), and those admitted to intensive care had more than triple the risk (HR, 3.10).
No increased diabetes risk was observed among people who were partially or fully vaccinated. In comparison, unvaccinated people with COVID infection had a 28% higher risk of type 2 diabetes (HR, 1.28).
“Altogether, our findings show reduction of risks over time, but the burden of mortality and health loss remains in the third year among hospitalized individuals,” the researchers write.
The findings build on a growing body of evidence that links COVID infection to type 2 diabetes. Multiple studies have reported elevated short-term risk of type 2 diabetes following COVID infection, but most have followed patients for less than 18 months.
A recent US Veterans Affairs analysis also evaluated three-year outcomes, but the participants were largely older White men, and the researchers did not account for vaccination status or certain medication exposures. In contrast, the current study included a more diverse population and accounted for vaccination status and severity of illness, offering a more detailed picture of how risk may change over time, the authors say.
