Longevity Briefs: More Than A Respiratory Disease – Measuring Cognitive Problems In Long Covid

Longevity briefs provides a short summary of novel research in biology, medicine, or biotechnology that caught the attention of our researchers in Oxford, due to its potential to improve our health, wellbeing, and longevity.

Why is this research important: Though classfied as a respiratory disease, it has become clear that COVID-19 affects many organs throughout the body, including the brain. Loss of the sense of smell (anosmia) is one of the most common neurological symptoms of COVID-19, and is sometimes the very first symptom to appear. However, many people report neurological symptoms such as difficulty concentrating, memory difficulties and fatigue that persist many months after their initial infection. These, along with other long term symptoms, are loosely termed ‘long COVID’.

While long COVID is most certainly real, the fact that most symptoms are self-reported, combined with disagreements over the exact symptoms and duration required to count as long COVID makes it difficult to measure just how common it is. Estimates suggest it occurs in around 10% to 25% of patients (more in those whose initial illness was severe) and that cognitive problems occur in around 70% of long COVID patients. However, important questions still need to be answered: how accurate are self-reported symptoms, and are the type/severity of the symptoms in long COVID related to those experienced during the initial infection?

What did the researchers do: In this study, researchers recruited 421 participants aged 18 and over. Of these, 181 had experienced COVID-19, 185 had not, and 55 had unknown infection status (they didn’t think they had had the disease, but had experienced a similar illness at some point). Of those who had had COVID, a majority (119) said that they continued to experience mild to severe symptoms. The participants then completed an online questionnaire and a series of cognitive tests designed to assess cognitive functions like memory, concentration and reasoning. Participants were followed up and the tests repeated at intervals, however this article concerns only the initial tests as the results of the follow-up have not been published yet.

Key takeaway(s) from this research: In the memory tasks, participants who had not had COVID-19 scored significantly higher after controlling for confounding factors (such as age and education) when compared to those who had had COVID-19. They also had faster reaction times in some of the memory tests. However, there were no significant differences in performance in any of the other tasks that could not be explained by confounding factors.

When comparing the performance amongst participants who had had COVID-19, the researchers found a significant association between reported severity of ongoing symptoms and poor performance. Once again, such associations were not found for the other tasks once confounding factors were controlled for.

There was also no significant association between the severity of the symptoms in the initial infection and poor cognitive function at the time of testing. However, there were some associations between the types of symptom experienced and subsequent cognitive function. Interestingly, the symptoms most strongly predictive of future reduced cognitive performance were skin-related (such as rashes and foot sores), with fatigue and body pains coming in second. Neurological symptoms were surprisingly less well correlated with reduced cognitive performance, with the notable exception of disorientation.

This study provides further evidence of measurable memory impairment in long covid, and suggests that while the severity of the initial infection was not linked to worse cognitive performance, the nature of the symptoms was. All in all, the findings are quite concerning as we don’t know how long-lasting these changes are, or whether there are other long-term consequences. The biggest concern would be that long covid might increase the risk of neurodegenerative disease in the future – a grim prospect given that as many as 1.3 million people in the UK alone (around 2% of the population) may have long covid according to a survey from the beginning of 2022.