People who catch Covid-19 have a greater risk of being diagnosed with diabetes and cardiovascular conditions for weeks after the infection has taken hold, according to a major UK study.

The risk of heart and circulation problems, such as irregular heartbeats and blood clots on the lungs, was nearly six times higher in Covid patients than uninfected people of the same age and sex, and 80% higher for diabetes, during the month after infection, researchers found.

Scientists compiled health records from more than 400,000 Covid patients in the UK and the same number of people who avoided the virus. The records were checked for new cardiovascular or diabetes diagnoses for up to 12 months, with the latest patient followed until January.

According to the analysis, the heightened risk of cardiovascular conditions fell back to normal seven weeks after testing positive for Covid, but for diabetes, the higher proportion of new diagnoses took nearly six months to return to baseline levels.

Dr Emma Rezel-Potts, an epidemiologist on the study at King’s College London, said: “This is really about doctors being aware of the potential increased risk for their patients, and in particular how they can reduce the risk of diabetes in the first three months after infection through an improved diet and taking exercise.”

While Covid can cause direct damage to organs and the circulatory system, Rezel-Potts stresses that many factors could explain the findings. For example, the Covid patients in the study were more likely to be overweight and had more underlying health problems than the uninfected control group, predisposing them to the further conditions. Some patients may have had undiagnosed diabetes or heart problems that only came to light when they caught Covid.

Although the reasons are uncertain, the researchers believe doctors should be vigilant for diabetes and cardiovascular disease when patients catch Covid, and remind them that simple lifestyle changes can help reduce the risk of further illness. The research was published in the journal Plos Medicine.

“It’s definitely reassuring that over the longer timeframe, cardiovascular disease and diabetes risk does seem to return to baseline levels,” said Rezel-Potts. “But we do have to be cautious in the acute period with cardiovascular disease and take note that the risk of diabetes seems to be elevated for several months, so that could be a good opportunity for risk prevention.”

Dr Faye Riley at Diabetes UK said there is mounting evidence that Covid could be triggering new cases of diabetes in some people, with the latest study shedding light on when and how long term the risk could be.

“While the growing evidence is concerning, it’s still unclear whether Covid-19 is directly causing new cases of diabetes, if it is bringing to light previously undiagnosed cases of diabetes, or if there are other factors in play. There’s also still a lot to learn about the types of diabetes that could be triggered by Covid-19,” she said.

“It’s important for everyone to be aware of the signs and symptoms of diabetes, such as unexplained weight loss, feeling thirsty or tired, or going to the toilet more often, whether you’ve had Covid-19 or not.

“It’s also important to understand your risk of developing type 2 diabetes and speak to your healthcare professional if you’re concerned about your risk if you’re recovering from Covid-19.”