New York, Oct 2 (IANS): Covid-19 infection triggers hyperglycemia, or high blood sugar levels, by disrupting key fat cells, bringing high risks of severe disease and death in many patients, according to a new study.

Hyperglycemia, the core feature of diabetes, is associated with inflammation and weakened immunity against infections, and was recognised as a significant risk factor for severe Covid-19 early in the pandemic.

However, doctors later began finding evidence that Covid-19 is associated with hyperglycemia in patients who have no history of diabetes.

In the study, reported in the journal Cell Metabolism, the researchers found that the deadly infection induces hyperglycemia by disrupting fat cellsa¿ production of adiponectin -- a hormone produced by fat cells which normally has a protective effect against diabetes by enhancing insulin sensitivity.

"We normally don't think that fat cells are very active, but in fact they synthesise many protective proteins for your body -- and it appears that SARS-CoV-2 may disable that protection in many patients," said James Lo, Associate Professor of medicine and cardiologist at the New York-Presbyterian/Weill Cornell Medical Centre.

For the study, the team analysed the records of 3,854 patients who were hospitalised with Covid-19 in the first few months of the pandemic in the US.

They found that a remarkably high proportion (49.7 per cent) of these patients presented with hyperglycemia or developed it during their hospital stays.

Compared to patients with normal blood sugar levels, the patients with hyperglycemia were nine times more likely to develop severe lung dysfunction (acute respiratory distress syndrome, or ARDS), 15 times more likely to be given mechanical ventilation, and three times more likely to die.

Further tests also revealed that the Covid-19 ARDS patients had severe declines in blood levels of adiponectin.

Hyperglycemia also occurs in patients with severe influenza or bacterial pneumonia, majorly by the death or dysfunction of beta cells that produce insulin, which is the principal hormone that regulates blood sugar levels.

"In contrast, hyperglycemia in Covid-19 patients is mainly caused by insulin resistance, in which insulin is present but the tissues it normally acts upon are no longer sensitive to it," said first author Moritz Reiterer, a postdoctoral fellow at the Centre.

"Patients with obesity, for example, may be more vulnerable to Covid-19 because they may already have some degree of insulin resistance and fat cell dysfunction, and possibly their fat cells are more susceptible to infection," added Lo.