Even a mild Covid-19 infection may cause brain damage, a study by Oxford University has found.
The study by Gwenaelle Douaud, associate professor with the Nuffield Department of Clinical Neurosciences, and her colleagues was based on a study of brain scan data from UK Biobank, a large databank of in-depth health information from more than half a million adults in Britain.
With the UK Biobank records, researchers identified 401 participants who had undergone brain MRI scans on an average of 38 months apart and whose health records showed they were infected with Sars-CoV-2, the virus that causes Covid-19.
The researchers also included a control group of 384 slightly older participants, who underwent the same MRI protocol but tested negative for Covid-19. The study participants were between 51 and 81 years old and the vast majority of the infected participants had not been admitted to the hospital or even showed symptoms.
To no surprise, the study revealed a “significant, deleterious” impact associated with Sars-CoV-2, mainly in brain areas that are responsible for emotions, memory and smell.
The group that had been infected with Sars-CoV-2 had a 1.3 to 1.8% loss of grey matter in the brain, compared to an estimated 0.2 to 0.3% loss of brain volume per year in normal middle-aged individuals.
The study also found that the overall size of the cerebellum, a brain region linked to cognition, had shrunk more in the infected participants.
These changes are associated with decline in cognition, which might lead to individuals taking longer to answer questions in standard cognitive tests.
The researchers also used people who developed pneumonia as a control group and concluded the brain change was specific to Covid-19 survivors.
Commenting on the findings, Douaud said that it is possible that these brain abnormalities might become less marked over time if the sense of smell was recovered.
“It is likely that the harmful effects of the virus, whether direct, or indirect via inflammation or immune reaction, decrease over time after infection. There is some indication, from small previous studies, that issues seen in functional brain imaging may improve in part more than 6 months after infection,” she said.
The overlapping smell and memory-related functions of the regions shown to alter significantly over time in Sars-CoV-2 raise the possibility that longer-term effects of Sars-CoV-2 infection might in time contribute to Alzheimer’s disease or other forms of dementia.
But the Oxford study, which involves subjects with mainly mild symptoms, did not show signs of memory impairment. The memory-related region in the brain did not show any change at a functional level.
“It remains to be determined whether the loss of grey matter and increased tissue damage seen in these specific limbic regions may in turn increase the risk for these participants developing memory problems,” the author wrote.