The study builds on previous research on diabetic patients.

One-in-10 COVID-19 patients with diabetes died in French hospitals, a far higher proportion than for patients without the condition, a May study in the same journal found.

One-in-10 COVID-19 patients with diabetes died in French hospitals, a far higher proportion than for patients without the condition, a May study in the same journal found. Exactly why high blood sugar increases COVID-19 death rates remains clear

Exactly why high blood sugar increases COVID-19 death rates remains clear.

The authors of Friday's study suggested that blood clotting, the weakening of blood vessel linings, and cytokine storm syndrome -- an overreaction of the immune system -- could all play a role.

The authors of the report urged hospitals to test all COVID-19 patients for glucose levels, as opposed to only those known to have diabetes.

The study, which looked at hospital patients admitted in January and February, had some limitations, experts not involved in the research said.

"This is a nice report but it is fully in line with expectations," Naveed Sattar, a professor of metabolic medicine at the University of Glasgow who was not one of the study's authors, said.

"What the authors cannot confirm is whether differential targeting of blood sugar levels in those admitted leads to differences in outcomes."

More research involving randomised controlled trials is needed, Bernard Khoo, a professor of endocrinology at University College London, commented.