PEOPLE who have Covid may suffer a “substantial drop” in their intelligence, a study has found.
It may explain why survivors battle “brain fog” in the weeks or months following, which causes people to think clearly or find the right words.
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Brain fog is one of the many symptoms reported by so-called long haulers of Covid, of which there are some one million currently in the UK.
It can also cause ongoing fatigue, breathing issues, muscle aches and heart palpitations.
The recent study examined the intelligence of more than 81,300 people, average age 46 years old, between January and December 2020 – mostly the first wave of Covid.
Of the participants, almost 13,000 had caught the coronavirus and five per cent said they had persistent symptoms.
The Great British Intelligence Test examines things like memory, reasoning, planning and problem solving but does not give an IQ score.
For example one task tests your ability to remember a certain number of items flashed on a screen, then pick them out from dozens of other items.
You can take the test yourself here, which will take around 30 minutes.
Researchers found those who had been diagnosed with Covid struggled more with tasks compared to those who never had the disease.
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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.
Their score fell “greater than the average 10-year decline in global performance between the ages of 20 to 70”, and more than in people who had suffered a stroke.
This was even after the researchers – including from the universities of Imperial College London and Cambridge – accounted for other factors that may influence intelligence, like education level.
People who had stayed at home showed a smaller but still significant deficit in their performance, as the researchers said even those with milder disease were implicated.
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.”
It could be that people are finding cognitive tasks difficult because of their other long Covid symptoms.
A high temperature or fatigue may make it harder to think clearly.
What’s more, the scientists claim brain fog could last for several years.
“Previous studies in hospitalised patients with respiratory disease not only demonstrate objective and subjective cognitive deficits but suggest these remain for some at 5-year follow-up”, the authors warned.
More research is needed to confirm the findings because the researchers can’t say with absolute certainty that Covid is the reason for the intelligence drop.
Only a small 275 participants took the test before and after contracting Covid.
This limits the ability to draw firm conclusions about “cause and effect”.
But the researchers are still confident in their findings, noting in their paper that the thousands of participants came from varying backgrounds.
The paper, published in The Lancet, is backed by other research using brain imaging which suggests “significant effects of Covid-19 in the brain”.
The preprint study, which has yet to be peer-reviewed, claimed diseases like Parkinson’s and dementia could be more likely to develop after Covid spreads through nerves in the brain.
The findings were based on scans of 782 participants before and after the Covid pandemic, of which 394 had tested positive for Covid.
“We identified significant effects of Covid-19 in the brain with a loss of grey matter in the left parahippocampal gyrus, the left lateral orbitofrontal cortex and the left insula”, the researchers wrote.
Grey matter is tissue that processes information in the brain.
Losing neurons that make up the grey matter lead to brain diseases like dementia.
Dr Rebecca Dewey, Research Fellow in Neuroimaging, University of Nottingham, supported the findings, telling Metro.co.uk: “This is incredibly good quality work, and I see no reason not to conclude that their findings are backed up by the data.”
But she added: “It absolutely does not show any cognitive differences. The authors state that and suggest that the research would be worth doing, but that is a different study.”
