COVID survivors have been warned that the brain could be irreversibly harmed by the virus.
The major organ has been shown in dozens of studies to be damaged in even the mildest forms of Covid illness.
A new study by researchers from the University of Oxford looked at people in the UK over the age of 50 who had mild Covid.
All 785 participants were in the UK Biobank, a large database for medical research, and had two brain scans 38 months aparts.
A total of 401 participants had tested positive for Covid in between the two scans.
The study found a number of effects on the brain, on average 4.5 months following infection.
Covid survivors had a greater reduction in grey matter thickness and tissue damage in regions of the brain associated with smell.
They had a reduction in whole brain size and, after performing a number of tests, showed a drop in cognitive function.
The effects ranged from 0.2 to 2 per cent additional change compared with the participants who had not been infected.
Professor Gwenaëlle Douaud, lead author on the study, said: “Despite the infection being mild for 96 per cent of our participants, we saw a greater loss of grey matter volume, and greater tissue damage in the infected participants.
“They also showed greater decline in their mental abilities to perform complex tasks, and this mental worsening was partly related to these brain abnormalities.
“All these negative effects were more marked at older ages.
“A key question for future brain imaging studies is to see if this brain tissue damage resolves over the longer term.”
It is not clear at this stage if the effects on the brain are reversible.
Professor Stephen Smith, senior author on the study, said: “The fact that we have the pre-infection scan helps us distinguish brain changes related to the infection from differences that may have pre-existed in their brains.”
The evidence is stacking up
Researchers at Tulane University reported findings last week based on studying primates, which are used in studies for the likeness to humans.
They found severe brain swelling and injury linked to reduced blood flow or oxygen to the brain.
They also found evidence of small bleeds, neuron damage and death - even in primates that didn't have a severe illness.
Lead investigator Dr Tracy Fischer said: "Because the subjects didn’t experience significant respiratory symptoms, no one expected them to have the severity of disease that we found in the brain.
“But the findings were distinct and profound, and undeniably a result of the infection.”
Meanwhile, researchers - including from the universities of Imperial College London and Cambridge - found that Covid can cause a a “substantial drop” in intelligence.
The findings came from a series of tests on memory, reasoning, planning and problem solving on more than 81,300 people.
People who had been on a ventilator during their Covid sickness were most likely to see a decline in scores.
In a classic intelligence test, they would have lost the equivalent of seven points in IQ, the team claimed.
The study said: "These results accord with reports of long-Covid, where 'brain fog', trouble concentrating and difficulty finding the correct words are common.
“The deficits were of substantial effect size for people who had been hospitalised.”
Another study reassured that “brain fog” shouldn’t persist for more than a year.
Covid patients scored significantly worse in episodic memory and in their ability to sustain attention on a task over time.
However, Professor Masud Husain, of Oxford University, said it was “encouraging” that most people’s attention and memory return “largely to normal in six to nine months”.
He said: “We still do not understand the mechanisms that cause these cognitive deficit.”
Explain this...
A team in the US suggested brain fog symptoms were the result of the organ being starved of oxygen.
After autopsying Covid victims, scientists at Johns Hopkins University School of Medicine found that large cells called megakaryocytes were taking up space and leaving less room for blood to pass through the brain freely.
According to Professor James Goodwin, the Director of Science and Research Impact at the Brain Health Network, it is thought that Covid gets into the brain through tightly sealed blood vessels which surround the organ.
But there is another explanation, he wrote in The Telegraph, and our own immune systems are to blame.
Sometimes the immune system goes into overdrive in response to a virus, releasing too many inflammatory molecules called cytokines.
This phenomenon, known as a cytokine storm, can injure healthy organs, including the brain, as well as the lungs and heart.
It has led to the death of many Covid victims, and those who survive may have long-term damage.
