The coronavirus may trigger diabetes in severe cases, research suggests.
In August 2020, scientists from Imperial College London warned the infection can cause type 1 diabetes in children, with new incidences doubling amid the pandemic.
A new study – published in the journal Nature Metabolism – has now revealed just under half (46%) of the 551 patients admitted to an Italian hospital with coronavirus complications developed high blood sugar levels, a common problem among people with diabetes.
These abnormalities persisted "for at least two months in [the] patients who recovered from COVID-19 [the disease caused by the coronavirus]".
With medics unsure how best to treat coronavirus-induced diabetes, one expert has warned "we may see a huge increase in the diabetic population".
In the UK, 3.9 million people had been diagnosed with diabetes in 2019, of whom around 90% had type 2.
Type 2 diabetes' onset is often linked to a patient's lifestyle, which may include carrying excess weight or being too sedentary.
Conversely, type 1 diabetes is an autoimmune disease that occurs when a patient's body mistakenly attacks insulin-producing cells. Insulin is a hormone that helps the body use sugar for energy, lowering levels in the blood.
People with diabetes are known to be more at risk of severe ill health with the coronavirus itself, with research increasingly suggesting the latter can also trigger the disease.
To better understand the emergence of diabetes amid the pandemic, scientists from the Boston Children's Hospital analysed 551 people who were admitted to a Milan hospital between March and May, 2020.
The patients were fitted with a sugar sensor upon admission and followed for up six months.
"These people were not diabetic before, but during admission, about 46% of the patients were found to have new hyperglycaemia," said lead author Dr Paolo Fiorina.
Hyperglycaemia is the medical term for high blood sugar levels. Over time, it can cause permanent damage to a patient's eyes, nerves, kidneys or blood vessels.
A sudden spike in blood sugar levels may trigger diabetic ketoacidosis – when the body breaks down fat for energy, which can lead to a coma – or a hyperosmolar hyperglycaemic state – severe dehydration as the body tries to rid excess sugar.
The hyperglycaemia patients also fared worse than those with normal glucose levels – including a longer hospital stay, more severe symptoms, and a higher need for oxygen, ventilation or intensive care.
Perhaps surprisingly, these patients were also found to be "severely hyperinsulinemic – they produced too much insulin", according to Dr Fiorina.
In addition, the hyperglycaemia patients produced abnormal levels of an insulin precursor and impaired islet beta cells, which make and secrete the blood sugar-lowering hormone.
"Basically, the hormonal profile suggests that the endocrine pancreatic function is abnormal in those patients with COVID-19 and it persists long after recovery," said Dr Fiorina. Insulin is made in the pancreas.
Coronavirus complications have long been linked to a patient's immune system over-reacting to the infection, leading to a cascade of inflammatory molecules that mistakenly attack healthy tissue.
The Boston scientists found blocking inflammatory immune proteins called cytokines improved the patients' blood sugar levels.
Other issues remained, however, with many of the patients enduring abnormally elevated glucose levels after eating.
"This study is one of the first to show that COVID-19 has a direct effect on the pancreas," said Dr Fiorina.
"It indicates the pancreas is another target of the virus affecting not only the acute phase during hospitalisation, but potentially also the long-term health of these patients."
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How these patients should be treated is something of a mystery.
"If you keep targeting and blocking insulin, but you have a strong and chronic inflammation, it may lead to chronic damage," said Dr Fiorina, who is calling for larger studies to test potential therapies.
He added: "When you consider how many patients have been hospitalised with COVID-19, and continue to be worldwide, we may see a huge increase in the diabetic population."
Although it is unclear why this may occur, the pancreas can express high levels of the so-called ACE2 receptor, which the coronavirus uses to enter cells. The virus has also been identified in the pancreas of people who died with the infection.
Inflammation triggered by a coronavirus patient's immune system may also damage the organ, affecting its ability to produce insulin.