sensory input. Particularly during the pandemic’s early waves, COVID-19 commonly caused people to lose their sense of smell.
Hellmuth cautions against seeing alarm in the findings. She notes that the average brain changes were “small,” and do not mean that people with mild COVID-19 face the prospect of brain “degeneration.”
The study, published online March 7 in the journal Nature, included 785 British adults aged 51 to 81. All had undergone brain scans before the pandemic, as part of a research project called the UK Biobank. They came back for a second scan during the pandemic.
In that group, 401 contracted COVID-19 at some point between the two brain scans, while 384 did not. Nearly all who fell ill — 96% — had a milder case. The second scan was taken an average of 4.5 months after their illness.
On average, Douaud’s team says, the COVID group showed greater tissue loss in specific brain areas related to smell, plus a bigger reduction in overall brain size.
The effect amounted to an extra 0.2% to 2% tissue loss, the investigators found.
Douaud agrees that a lack of sensory input might explain the changes in smell-related brain areas. But, she says, her team did not know whether participants had, in fact, lost their sense of smell. So they could not look for correlations between those symptoms and brain changes.
The researchers were able to look at participants’ performance on some standard tests of