Scientists have been studying the effects of Covid-19 on the brain (PA/Getty)

The long-term effect of a Covid-19 infection could include a drop in intelligence, according to new research.

Between January and December last year, scientists conducted the Great British Intelligence Test that examined the IQ of 81,337 people.

Among that number were 13,000 who had been infected with the virus.

Once the scientists had factored out things like age, sex, language and education level, they found people recovering from Covid saw the biggest decline.

Tasks requiring problem solving, planning and reasoning were harder for them than for people who hadn’t had the virus.

In the worst cases, when people had been on a ventilator to beat the disease, the researchers recorded a seven-point drop in intelligence.

The data was collected together and published in a study called: Cognitive Deficits In People Who Have Recovered From COVID-19′.

It was published in the medical journal the Lancet and involved researchers from Imperial College London, Kings College and the Universities of Cambridge, Southampton and Chicago.

‘These results accord with reports of long-Covid, where ‘brain fog’, trouble concentrating and difficulty finding the correct words are common,’ the authors wrote.

‘The deficits were of substantial effect size for people who had been hospitalised.’

The scientists suggest that one reason for the intelligence drop was the continued effect of the virus on our ability to think clearly.

For example, it’s much harder to concentrate if you’re suffering from a high temperature or respiratory problems because you’ve got long Covid.

‘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 note.

The researchers urge caution on drawing too many conclusions without brain imaging data. Instead, they say the results should act as a clarion call for further research into the issue.

Interestingly, separate research on the effects of long Covid on the brain has taken imaging into account.

A preprint study, which has yet to be peer-reviewed, has been published suggesting neurodegenerative diseases (for example: Parkinson’s, Alzheimer’s or cancer) could be more likely to develop after Covid spreads through nerves in the brain.

‘UK Biobank scanned over 40,000 participants before the start of the Covid-19 pandemic, making it possible to invite back in 2021 hundreds of previously-imaged participants for a second imaging visit,’ the academics wrote in their paper.

‘Here, we studied the effects of the disease in the brain using multimodal data from 782 participants from the UK Biobank Covid-19 re-imaging study, with 394 participants having tested positive for SARS-CoV-2 infection between their two scans.

‘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.’

Grey matter is the part of the brain containing all its nerve synapses and most of its cell bodies. The latter includes microglial cells which are the brain’s version of white blood cells that help it to fight off diseases.

Therefore, any damage to or loss of grey matter can impair someone’s ability to function.

Interestingly, the authors of this study can’t say for sure that there is any loss of cognitive function, despite damage to grey matter. That seems to go against the findings suggested by the Lancet paper.

Brain scans taken before and after a Covid infection give some clues about the effects of the disease on our nervous system (Getty Images/Cultura RF)

Brain scans taken before and after a Covid infection give some clues about the effects of the disease on our nervous system (Getty Images/Cultura RF)

‘As this study is observational (as opposed to a randomised, controlled, interventional study), one cannot make claims of disease causality with absolute certainty, but interpretational ambiguities are greatly reduced compared with post hoc cross-sectional studies,’ the authors explain.

But despite it being a non-peer reviewed and observational study, the findings have been given backing by other experts.

Dr Rebecca Dewey, Research Fellow in Neuroimaging, University of Nottingham, told ‘This is incredibly good quality work, and I see no reason not to conclude that their findings are backed up by the data.

‘This has been very carefully and meticulously undertaken, and uses the framework set up around Biobank, which was designed and approved by a consortium of some of the best scientists in the relevant fields.

‘Experimentally, I think every potential confound has been controlled for.

‘I guess you could note that the original pool of participants in Biobank (the 40,000 people scanned before the pandemic) is a self-selecting sample, with potential differences in characteristics from those of the general population, but the authors did attempt to correct for background bias.

‘Further the findings are based on longitudinal changes over time that are associated with contracting Covid, and so this is unlikely to impact one group (i.e. Covid or control) any more than the other (i.e. it would be difficult to argue that participants in Biobank are any more or less likely to have mild/severe Covid, or undiagnosed Covid).

‘As such, the results seem pretty robust as they’re in a large sample and any systematic biases have largely been excluded.’

She continued: ‘I have slightly less faith in the differences reported between hospitalised and non-hospitalised due to significant differences between groups (particularly in age) but looking at their control methods and findings, these differences have probably served to muddy the water rather than falsely amplify any reported effects of Covid.

‘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. The brain is highly adaptable and may be able to compensate for any physiological changes reported here.’

The Office of National Statistics reported last month that almost one million people in the UK were living with ongoing symptoms after Covid-19 in the four-week period ending 6 June.

And 33,000 of them are under 16 and another 200,000 are between 17 and 35 years old.

Of those million, almost 400,000 had been living with symptoms – most commonly fatigue, breathlessness, muscle aches and brain fog – for more than a year and over 600,000 said symptoms negatively impacted their daily lives.

Speaking as part of Independent SAGE, Professor Christina Pagel says the UK needs to factor long Covid into future policy decisions.

‘The formal roadmap criteria currently only explicitly considers hospitalisations, and how these are affected positively by current vaccines or negatively by variantseven though Chris Whitty and SAGE have all warned about long Covid’s potential long term awful impact on a generation of young people,’ she wrote in

‘The problem has been that long Covid is hard to measure because it takes several months to establish (by definition), it can appear in so many different ways and there is no simple test for it.

‘Because of this, and because it only started being recognised as a serious problem last summer, it’s not included in any of the Government’s daily or weekly statistics, which typically include new infections, hospitalisations, deaths, vaccinations and demographic data on spread.’

‘But it matters. Almost half a million of those living with long Covid were 17 to 50 years of age – impacting people’s ability to study or work.’

MORE : What is Covid brain fog?

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