It’s been known for some time that already having diabetes can increase your risk of severe illness and death from Covid-19.

A draft study by the University of Oxford and the London School of Hygiene and Tropical Medicine looking at 17 million NHS records suggested that people with “uncontrolled” diabetes (where your blood sugar is too high despite treatment) were 2.5 times more likely to die with coronavirus than people of the same age and sex without diabetes.

But in recent days, there have been reports suggesting coronavirus could actually cause diabetes in previously healthy patients. Researchers say they will look at whether coronavirus might trigger “classic type 1 or type 2 diabetes or a new type of diabetes” as part of a global investigation.

Let’s take a look at what we know – and what we don’t.

What’s the evidence?

On 12 June, sixteen academics from around the world wrote to the New England Journal of Medicine outlining a possible biological mechanism by which Covid-19 might trigger diabetes.

The researchers say that “new-onset diabetes and severe metabolic complications of preexisting diabetes […] have been observed in patients with Covid-19”.

They refer to three papers as evidence of this claim. Only one of them describes possible “new-onset diabetes” in a previously healthy patient – it’s a case study looking at a single patient in China.

The other two reports looked at groups of patients who already had diabetes to see whether coronavirus might make the condition worse.

As Dr Gabriela da Silva Xavier, senior lecturer in cellular metabolism at the University of Birmingham, points out: “none of the studies cited explicitly describe diabetes brought on by Covid-19”.

He says: “it would be unfair to take the cited data to indicate that Covid-19 is causal of diabetes and diabetes complications”. Nevertheless, he says “it is reasonable to propose to look at this carefully”.

Dr Riyaz Patel, associate professor of cardiology and consultant cardiologist at University College London Hospital, said: “There is no robust data yet to indicate that Covid-19 causes new diabetes or worsens existing diabetes.  Some data however suggests there could be a possible link so researchers are seeking to explore this further.”

Dr Patel points out that there are some confounding factors when it comes to diabetes and coronavirus.

“We know that any stress inducing illness can cause blood sugar levels to temporarily rise and we see this for example with heart attacks. Also people who are more likely to get very sick with Covid may be at risk of developing diabetes anyway perhaps because they are overweight.”

That means it’s hard to tell whether someone has diabetes because of a coronavirus infection, or whether it was brought on by other factors – like weight – that can increase the chance of both (Type 2) diabetes and severe Covid-19 illness.

And Lora Heisler, professor of human nutrition at the University of Aberdeen, identifies another possible challenge: “trying to figure out whether the diabetes is actually new before Covid-19 because some people may have undiagnosed diabetes.”

When will we know more?

Naveed Sattar, professor of metabolic medicine at the University of Glasgow, said: “This is definitely an important question that many doctors are watching but we need to see what happens to diabetes rates over the next 1-2 years to confirm or refute such risks.”

The researchers who wrote to the NJEM are establishing a global database with other experts to track cases of “Covid-19-related diabetes”, which they hope will give more insight. They say they will look at whether coronavirus might trigger “classic type 1 or type 2 diabetes or a new type of diabetes” as part of the investigation.

FactCheck verdict

Several media outlets have reported that coronavirus could trigger diabetes in previously healthy patients after a group of scientists wrote to a leading medical journal on the topic.

The scientists did not cite any definitive evidence of this having happened: the closest they got was a paper looking at a single patient in China.

However, they did outline a biological mechanism by which Covid-19 might bring on diabetes and/or aggravate existing diabetes.

Other experts agree that this is a question worthy of investigation, but it could be some time before we get clear answers. The researchers who wrote to the journal have established a global database to track potential cases of “Covid-19-related diabetes”, which they hope will shed more light.