The study provides additional evidence of the effects of COVID throughout the body, some of which may have permanent repercussions on a patient’s health.

The study of 785 volunteers, aged 51 to 81, was conducted in conjunction with U.K. Biobank—an initiative to catalog the health information of half a million U.K. residents. Researchers compared two MRI scans of each subject’s brain, taken 38 months apart, with the first scan conducted before the pandemic began. In the intervening period, 401 of the volunteers had tested positive for COVID, providing a test and control group for the effects of the coronavirus on the brain.

Under normal circumstances, people lose about 0.2 to 0.3% of their brain matter each year through aging. Yet the study found that COVID patients experienced an additional loss of anywhere between 0.2 to 2% of their brain size in the three years between MRI scans. At worst, that is a loss equivalent to your brain shrinking over 10 years.

Only 15 of the volunteers who tested positive for COVID needed to be hospitalized due to the virus, meaning that even mild cases led to noticeable loss of brain matter. 

Researchers also found damage in the areas of the brain responsible for smell, which may help to explain one of the most commonly reported COVID symptoms: the loss of smell and taste.

“This is pretty convincing evidence that something changes in the brains of this overall group of people with COVID,” Dr. Serena Spudich of the Yale School of Medicine, who was not involved in the study, told the New York Times. 

Despite being known primarily as a respiratory illness, COVID attacks several parts of the body besides the lungs. A study late last year found that the coronavirus could attack fat cells directly, perhaps explaining why overweight and obese patients have been more susceptible to severe COVID. 

COVID patients can suffer from a wide range of chronic conditions months after testing positive, including depression, hair loss, and fatigue. COVID has also been correlated with higher rates of cardiovascular disease and heart attacks. Even mild cases appear to trigger instances of “long COVID,” contributing to a public health phenomenon that threatens to drag on economies post-COVID.

Still, scientists cautioned against linking a reduction in brain matter to cognitive decline. Spudich said to Bloomberg, “We are fortunate to have extremely resilient brains that can function with many potential insults without experiencing any impairment.” 

More research is required to determine whether the shrinking effects of COVID on human brains is permanent too. As neuroscientist Gwenaëlle Douaud, one of the authors of the study, said, “The brain is ‘plastic’ and can heal itself.”