Even mild cases of Covid can have long-lasting effects and scientists warn the virus could bump up diabetes cases.
A study found people infected by the bug are 28 per cent more likely than average to develop type 2 diabetes.
The illness affects around five million people in the UK and means the body cannot properly process sugar or carbs from food.
Doctors at Heinrich Heine University in Germany said swelling triggered by the immune reaction to coronavirus can damage cells that produce insulin, the hormone that controls sugar absorption.
In a study of 35,865 people who tested positive for coronavirus, they found the risk of developing type 2 diabetes was 28 per cent higher than in people who never had the bug.
Professor Wolfgang Rathmann said: “Covid infection may lead to diabetes by upregulation of the immune system.
“Patients may have been at risk for developing diabetes due to having obesity or pre-diabetes, and the stress Covid-19 put on their bodies speeded it up.”
He said weight gain and less exercise during lockdowns may have made the problem worse, with both known to raise diabetes risk.
Writing in the journal Diabetologia, Professor Rathmann said the same effect was not seen after other chest infections.
There are thought to have been around 42million Covid infections in England so far – including reinfections – putting millions at risk.
Type 2 diabetes is common but it is linked to a higher risk of strokes, heart disease and cancer.
Dr Faye Riley, of Diabetes UK, said: “This study, and others, hint that coronavirus could be triggering type 2 diabetes.
“But it’s not yet clear if the virus is causing new cases of type 2 diabetes, bringing undiagnosed cases to light, or temporarily driving up blood sugar levels.”