A cohort of scientists from across the world believe that there is a growing body of evidence that Covid-19 can cause diabetes in some patients.
Prof Francesco Rubino, from King’s College London, is leading the call for a full investigation into a possible link between the two diseases. Having seen a rise in both type 1 and type 2 diabetes in people who have caught coronavirus, some doctors are even considering the possibility that the virus ‒ by disrupting sugar metabolism ‒ could be inducing an entirely new form of diabetes.
Rubino first realised the possibility of a link during a tea party with colleagues over Zoom where anecdotal cases were being exchanged.
Rubino and others set up a registry to start pooling and analysing these reports. The principal investigators of the registry which has received reports from more than 350 individual clinicians who suspect they have encountered one or more cases of Covid-induced diabetes — have said the numbers were hard to ignore.
“Over the last few months, we’ve seen more cases of patients that had either developed diabetes during the Covid-19 experience, or shortly after that. We are now starting to think the link is probably true – there is an ability of the virus to cause a malfunctioning of sugar metabolism,” said Rubino.
If there was a biological link, it would be difficult to prove without a substantial database, he noted. “We said it’s worth embarking on an investigation because this – especially given the size of the pandemic – could be a significant problem.”
Patients with pre-existing diabetes have a higher risk of serious complications with Covid-19 and are on the UK priority list to receive the vaccine. Links between other viruses and diabetes, and the way the Sars-CoV-2 virus that causes Covid-19 penetrates multiple organs has triggered concern.
“In my own mind, there’s no doubt. Covid-19 is certainly a cause of new diabetes,” said Paul Zimmet, professor of diabetes at Australia’s Monash University. “But we don’t yet fully understand — firstly, the magnitude and, secondly, which of the things that we’ve hypothesised are the major factors.”
Scientists have hypothesised that since Sars-CoV-2 interacts with a receptor called ACE-2 to infiltrate cells in a range of organs, including the pancreas, it could be disrupting the sugar metabolism. Another potential explanation is the body’s exuberant antibody response, which is meant to fight the virus, overreacts and attacks the organs key to maintaining normal glucose levels.
“Now, these are all theories … theories that are not philosophical but grounded in biology and experience with other viruses,” said Rubino, who is chair of metabolic and bariatric surgery.
Other viruses – particularly enterovirus infections – have been associated with causing type 1 diabetes, in which the body attacks the cells in the pancreas thwarting the production of insulin. Enterovirus antibodies have been recorded at higher levels in pregnant mothers of children that have gone on to develop type 1 diabetes, and more enterovirus infections tend to be detected in children who develop the condition, compared with siblings that don’t.
Dr Sathish Thirunavukkarasu, an investigator at Canada’s McMaster University, has conducted a review encompassing eight studies from different countries from the first five months of the pandemic. Thirunavukkarasu and colleagues found a combined 492 cases of newly diagnosed diabetes among 3,711 hospitalised Covid-19 patients, or a pooled proportion of 14.4%.
These figures include both Covid-19 patients who were diagnosed with diabetes for the first time, as well as people who previously had diabetes – but didn’t know they had the disease, he explained.
It’s hard to ignore the dramatic symptoms of type 1 diabetes, where the body does not make any insulin. But in the case of type 2 diabetes – in which the body is unable to make enough insulin or the insulin doesn’t work properly – symptoms are easy to miss because they appear gradually.
About 3.9 million people in the UK have been diagnosed with diabetes as of 2019, but doctors believe there are thousands who remain undiagnosed, a statistic that has probably worsened because of the pandemic.
Ian Braithwaite, an NHS doctor and co-founder of Habitual, a diabetes prevention and reversal company, pointed out that the analysis by Thirunavukkarasu and colleagues was also limited to patients in hospital, so it wasn’t clear if the cases of diabetes persisted as they recovered, or whether the rise in sugar levels puts patients at risk for diabetes.
A rise in sugar levels could have nothing to do with diabetes and everything to do with the body’s response to infection. In addition, steroids that are used to treat certain patients with Covid-19 are also known to raise blood sugar levels, doctors have highlighted.
Other recent studies have linked Covid-19 with new-onset diabetes to varying degrees. Researchers in China who tracked 2,469 Covid-19 patients after they were discharged from hospital for six months recorded 58 (roughly 2.35%) cases of new-onset diabetes. A separate still to be peer-reviewed study that looked at the outcomes of 47,780 Covid-19 patients within five months of hospital discharge in England found that 4.9% of patients were diagnosed with diabetes post-discharge.