Survivors of Covid-19, even those who had just mild cases of the virus, can lose gray matter in their brains equivalent to ten years of aging, a new study says.
The study, which was published on Monday in the journal Nature, an effort to pin down the difficult diagnosis of “long Covid,” is thought to be the largest of its kind.
The study showed that the brains of people who had recovered from Covid-19 had suffered a greater loss of gray matter and indicated a larger presence of abnormalities in brain tissue compared with those who had avoided the disease.
Perhaps unsurprisingly, many of the physiological changes noted by the researchers were in the area of the brain that is connected to the sense of smell; this sense is often one of the first symptoms of Covid that patients notice after contracting it.
Clear differences in the brain after mild Covid infection
Gwenaëlle Douaud, an associate professor of neurosciences at the University of Oxford, told CNN in an interview “We were quite surprised to see clear differences in the brain even with mild infection.”
Douaud and her team studied brain imaging from 401 people who recovered from Covid-19 between March of 2020 and April of 2021; images had been taken both before infection and afterward, approximately 4½ months after they had been infected.
The researchers compared what they found with imaging taken of 384 uninfected people who were similar in age, socioeconomics and risk factors, including blood pressure and obesity, which are both complicating factors for Covid-19.
Fifteen of the 401 infected people in the first group had been hospitalized.
All 785 participants in the brain study were adults, between the ages of 51 and 81; they were also part of the UK Biobank, a government-run health database including information from some 500,000 people.
Normally, as part of the aging process, people lose between 0.2% to 0.3% of gray matter every year in the areas of the brain that deal with memory. However, Douaud states that the people studied lost an additional 0.2% to 2% of tissue compared with those who hadn’t suffered from the coronavirus.
And it wasn’t just interpretations of imaging that led to these findings; Douaud and her team also tested study participants for executive and cognitive function using something called the Trail Making Test, which is often used in the diagnosis of cognitive impairments that may be a part of dementia. It also tests the processing speed and function of our brains, according to the CNN report.
And the findings confirmed the suspicions of the researchers; they found that the patients who had undergone the greatest amount of brain tissue loss also had the worst scores on this exam.
Despite the areas of the brain being most affected related to the olfactory system, Douaud maintains that the reason for this is not clear.
“Since the abnormal changes we see in the infected participants’ brains might be partly related to their loss of smell, it is possible that recovering it might lead to these brain abnormalities becoming less marked over time.
“Similarly, it is likely that the harmful effects of the virus (whether direct, or indirect via inflammatory or immune reactions) decrease over time after infection. The best way to find out would be to scan these participants again in one or two years’ time,” she said.
Unclear why there is a connection between infection and brain function
The researchers plan to have the participants undergo additional imaging and retesting after one or two years.
Much remains unclear after the study, which raises tantalizing questions. It is still unknown why there is some connection between infection and brain function.
In addition, while studies have shown people with significant, repeated loss of smell also suffer from a loss of gray matter, the new study did not evaluate whether or not the subjects actually suffered from a loss of smell.
Still, the findings raised alarm bells in the medical world, with the authors of the paper saying that they “raise the possibility that longer-term consequences of SARS-CoV-2 infection might in time contribute to Alzheimer’s disease or other forms of dementia.”