While Covid-19 no longer poses the urgent public-health threat it once did, recent research points to a good reason to keep the virus in mind: it could leave a lasting stamp on yours, and possibly even be a catalyst for dementia, say experts.
Studies suggest that it is associated with possibly long-lasting changes to the brain, potentially contributing to cognitive problems like brain fog, mental fatigue and memory loss, as well as neurological and mental-health issues, reports TIME.
The virus seems able to damage blood vessels and support cells in the brain and may kickstart changes to the immune system that also affect brain function, said Dr Wes Ely, co-director of the Centre for Critical Illness, Brain Dysfunction, and Survivorship at Vanderbilt University Medical Centre.
What does that mean for the average person as the virus once again circulates widely? Many people of all ages recover just fine, mentally and physically, after a Covid-19 case.
But lingering cognitive effects are a real risk, particularly for older people, Ely said. Older adults are more likely to experience severe Covid, which has long been linked to a higher risk of long-term complications.
And they may have had pre-existing cognitive issues that worsen after infection.
“They don’t have as far to fall before they experience a clinical awareness that they’re having problems,” Ely added.
Research has shown that a Covid-19 case can accelerate mental decline in older adults with dementia. The virus may also raise the chances of developing dementia for the first time, suggests a research review of 11 previous studies that was posted online in February before being peer-reviewed.
Adults over 60 who survived Covid-19 had a significantly higher risk of developing dementia a year later, compared with similar-aged people who hadn’t had a respiratory infection.
Cognitive impairment was almost twice as likely among people who’d had Covid as an uninfected control group.
Dan Shan, co-author of the study and a former junior researcher at Columbia University, said more research was needed to confirm whether the virus was directly causing dementia, but his team was “pretty confident” there’s a connection.
This link may not be unique to the virus that causes Covid-19. “Numerous studies have shown that respiratory infections like flu can lead to greater risks of cognitive deficits or dementia,” Shan said. “However, these findings haven’t captured public attention as much as Covid-19.”
Age may be an important risk factor for cognitive issues, but younger people shouldn’t feel immune from Covid-19’s effects, either, Ely said.
“There are people in their 30s and 40s with neurocognitive deficits that look like mild dementia.”
A large study published in the New England Journal of Medicine in February backs up that warning. It suggests that Covid-19 can hinder cognitive performance among adults of all ages, even those who ostensibly recover fully.
In that study, more than 100 000 adults in the UK took tests meant to measure cognitive skills.
When the researchers compared people who’d had Covid-19 with demographically similar people who’d never had a confirmed case, they found that the Covid survivors, on average, performed worse “across the board, but particularly on measures of memory function, executive function – for example, your ability to decision-make and plan – and reasoning”, said study co-author Adam Hampshire, a professor of cognitive and computational neuroscience at King’s College London.
The study didn’t measure differences in individual participants’ performance pre- and post-Covid, and the results don’t necessarily mean that every single person who catches Covid-19 will experience cognitive decline, Hampshire said.
But when looking at the study group as a whole, there were clear differences between those who’d had Covid-19 and those who hadn’t. The results equated to about a three-IQ-point deficit among people who recovered completely versus those who'd never had the virus.
Among people with unresolved long Covid symptoms and those who’d been admitted to the ICU, the deficits jumped to six and nine IQ points, respectively.
But there are some reasons for optimism. In the study, cognitive differences were not as pronounced among people who’d been vaccinated multiple times, nor those who got Covid later in the pandemic, suggesting risks may be lower now than they were in 2020.
The researchers also didn’t find a dramatic difference between people who’d been infected once versus multiple times. (Other studies, however, have found that repeat infections carry compounding risks of brain complications, as well as other serious health problems.)
And people who had long Covid symptoms but eventually got better “performed at the same [cognitive] level as people who had shorter-duration symptoms”, which suggests some effects of long Covid may be reversible, Hampshire says.
The data on Covid-19 and cognition are worrying, but more research is required to fully assess the long-term effects of the virus.
“These relationships need to be observed over a longer period, potentially five to ten years, to fully understand the impact of Covid-19 on the development of new-onset dementia, a condition that progresses slowly,” Shan said.
Research on if and how Covid-related brain damage can be reversed is ongoing and provides reason for hope, Ely said.
But for now, the cognitive risks of Covid-19 are yet another reason to stay up-to-date on vaccines and avoid infection if at all possible.
Study details
Temporal Association between COVID-19 Infection and Subsequent New-Onset Dementia in Older Adults: A Systematic Review and Meta-Analysis
Dan Shan, Congxiyu Wang, Trevor Crawford et al.
Published online The Lancet Preprint 6 February 2024
Abstract
Background
The relationship between Covid-19 infection and the increased likelihood of older adults developing new-onset dementia (NOD) remains elusive. This review primarily aimed to investigate the potential role of Covid-19 in leading to NOD among older adults aged 60 and older over various time intervals.
Methods
A thorough search was performed across several databases including MEDLINE/PubMed, PsycINFO, Scopus, medRxiv, and PQDT Global for studies published in English from January 2020 to December 2023. We assessed the risk of developing NOD, using Risk Ratio (RR) for measurement. The control groups were categorised as: (i) a non-Covid cohort with other respiratory infections [control group (C1)]; and (ii) a non-Covid cohort with otherwise unspecified health statuses [control group (C2)]. Follow-up periods were divided into intervals of 3, 6, 12, and 24 months post-Covid.
Results
Our review incorporated 11 studies, encompassing 939,824 post-Covid-19 cases and 6,765,117 controls. The overall pooled analysis revealed a significant link between Covid-19 infection and an increased risk of NOD (RR = 1.58, 95% CI 1.21–2.08). In subgroup analyses, NOD risk was significantly higher in the Covid-19 group compared to C2 at 12 months post-Covid (RR = 1.84, 95% CI 1.41–2.38), but not at 3 (RR = 0.87, 95% CI 0.46–1.65) or 6 months (RR = 1.73, 95% CI 0.72–4.14). Compared to C1, the risk increase was not significantly remarkable at 3 (RR = 0.94, 95% CI 0.35–2.57), 6 (RR = 1.13, 95% CI 1.07–1.20), and 12 months (RR = 1.12, 95% CI 0.91–1.38), and overall (RR = 1.13, 95% CI 0.92–1.38). Female had a significantly higher risk of developing NOD in the Covid-positive group (RR = 1.65, 95% CI 1.53–1.78) and C2 group (RR = 1.33, 95% CI 1.22–1.44). Patients with severe Covid-19, as classified by the American Thoracic Society guidelines, were significantly much more prone to developing NOD than those with non-severe infections (RR = 17.58, 95% CI 10.48–29.49). Cognitive impairment was nearly twice as likely in Covid-19 survivors compared to those uninfected (RR = 1.93, 95% CI 1.52–2.43).
Discussion
Covid-19 infection may be linked to a higher risk of NOD in recovered old adults at the subacute and chronic stages following Covid-19 diagnosis. This risk appears to be on par with that associated with other respiratory infections.
See more from MedicalBrief archives:
COVID-19’s cognitive cost may be equivalent to 10-years ageing — UK intelligence test data
Brain health of over-50s slumped during pandemic – UK study
Cognitive problems from severe COVID similar to 20 years of ageing – UK study