Although diabetes is a known risk factor for mortality from Covid-19, that risk is decreased threefold among diabetes patients who were taking metformin prior to contracting the virus, researchers from the University of Alabama at Birmingham found.

Their study looked at more than 25,000 Covid-19 cases that came to their university’s hospital from February through June. Consistent with other studies, they found a higher ratio of Covid-19 patients were Black, obese or had hypertension or Type 2 diabetes. They also found that diabetes was associated with “a dramatic increase in mortality,” but with an exception.

“Interestingly, we found that metformin treatment prior to diagnosis of Covid-19 was independently associated with a significant reduction in mortality in subjects with diabetes and Covid-19,” they wrote. “This risk is dramatically reduced in subjects taking metformin prior to diagnosis of Covid-19, raising the possibility that metformin may provide a protective approach in this high risk population.”

Confirms studies done elsewhere

In fact, they found the mortality risk was reduced roughly threefold in patients who had been taking metformin before being diagnosed with Covid-19, a finding similar to ones reported in China, France and in a study done in the US that looked at 6,256 patients from all 50 states.

“The fact that such similar results were obtained in different populations from around the world suggests that the observed reduction in mortality risk, associated with metformin use in subjects with T2D and COVID-19, might be generalizable,” they wrote.

Why it works is unclear

Why or how metformin provides this protection is unclear, although the authors noted that the common diabetes drug has previously been found to have an anti-inflammatory and anti-thrombotic effect. An excessive inflammatory response have been a deadly complication from Covid-19. They note, too, that metformin has previously been associated with reduced mortality in medical and surgical intensive care patients with Type 2 diabetes who were taking it prior to admission.

In its analysis of Covid-19 patients, the University of Alabama researchers found that prior metformin use reduced patients’ risk of dying to 11 percent, similar to a general Covid-19-positive population.

That’s “dramatically lower” than the 24 percent mortality it found for Covid-19 patients with diabetes who were not on metformin.