One of the weirdest symptoms of Covid disease – the loss of smell It’s a symptom that, long before the epidemic, was considered a warning sign of dementia.
The big question for researchers now is whether the loss of smell associated with Covid could also be associated with cognitive decline. Around 5% of Covid patients worldwide About 27 million people report loss of smell for more than six months.
See the new preliminary results on Sunday at Alzheimer’s Association International Conference In San Diego, they suggest there may be a link, although experts warn that more research is needed.
the old Look for Some Covid patients have been found to develop cognitive impairment after infection. In the new study – which has not been published in a peer-reviewed journal – Argentinian researchers found that loss of smell during Covid may be a stronger predictor of cognitive decline, regardless of the severity of the illness. sickness.
Study co-author Gabriela Gonzalez Aleman, a professor at the Pontificia Universidad Catolica Argentina in Buenos Aires, said it was too early to say whether the cognitive impairment is permanent.
The study followed 766 adults aged 55 to 95 for one year after infection. Almost 90% have a confirmed case of Covid and all have undergone regular physical, cognitive and neuropsychological tests over the course of a year.
Two-thirds of those diagnosed had some form of cognitive impairment by the end of this year. In half of the participants, the vulnerability was severe.
The researchers did not have solid data on the state of the patients’ cognitive function before they contracted Covid to compare with the outcome at the end, but they asked the families of the participants about their cognitive function before the infection. and did not include people who had them. Perceptual impairment evident prior to study.
According to Jonas Olofsson, professor of psychology at Stockholm University, who studies the association between Smell and risk of dementia – And he wasn’t involved in the new research, loss of smell is a well-established precursor to cognitive decline. It’s also well established that Covid can lead to permanent loss of smell, he said.
“The question is whether these two lines of research intersect,” Olofson said. “This study is very puzzling, although the information I have seen so far does not allow for strong conclusions.”
Connection of scent with the brain
According to the doctor. Claire Sexton, senior director of science and outreach programs at the Alzheimer’s Association, “loss of smell is a sign of an inflammatory response in the brain.”
“We know Inflammation is part of the neurodegenerative process in diseases such as Alzheimer’s diseasesaid Sexton. But we need to dig deeper into their exact relationships. »
A separate study – unrelated to Covid – was published last Thursday in the journal Alzheimer’s disease and dementia This contact probes further. Researchers at the University of Chicago have found that not only can a decrease in sense of smell over time predict loss of cognitive function, but loss of sense of smell could also be a harbinger of changes structures in brain regions important in Alzheimer’s disease and Alzheimer’s disease. .
Using data from the Rush University Memory and Aging Project, researchers tracked the loss of sense of smell in 515 older adults over a 22-year period. They also measured volume of gray matter In parts of the brain that have been linked to dementia and those linked to smell.
They found that people whose sense of smell declined faster over time ended up with smaller amounts of gray matter in both regions of the brain. The same was not true of parts of the brain associated with vision, suggesting that smell has a unique association with perception in terms of structural differences.
“The change in olfactory function over time can not only predict the development of dementia, but can also predict the size of important brain regions,” said Dr. Jayant Pinto, Director of Rhinology and Allergology at UChicago Medicine.
“Critical” smell for perception
Pinto said Covid is not the first virus to cause smell loss, but virus-associated smell loss was a rare event before the outbreak hit. This means that scientists have only recently been able to carry out major studies on how the loss of smell caused by the virus affects cognition.
“Smell is essential for cognition, especially for the brain to process information about the environment. If you disable this channel of communication with the brain, you will suffer,” said Dr. Carlos Pardo, professor of neuroscience at Johns. Hopkins University, which was not involved in any of the studies.
But if the loss of smell associated with Covid can cause cognitive decline remains uncertain.
“It’s an open question – damage to the olfactory system from SARS-CoV-2 leads to problems not only in the olfactory system, but also in the brain itself?” said Pinto.
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According to Olofson, the olfactory system — the parts of the brain associated with smell, including the olfactory bulb, the part of the brain that processes smell — communicates with the parts of the brain that process memory. While it’s possible that Covid disrupts the olfactory bulb and then damages the brain around it, Olofsson said that’s unlikely.
“There are several other ways these two things can be linked. The cause could be an illness unrelated to the impact of Covid.
Or, Covid could simply amplify the current loss of smell or cognitive decline that went unnoticed before infection, Olofson said. Patients may have already experienced some cognitive decline when they contracted Covid, or they may already have had a slight impairment in their sense of smell, which made them more susceptible to Covid-related loss of smell.
“It could be that the olfactory function was preserved despite his atrophy, but when the Covid arrived, it ended,” he said.
If Covid loss of smell can lead to cognitive impairment, understanding the link could help clinicians intervene in early loss of smell and potentially prevent cognitive decline in people at high risk.
“We are going to face an epidemic of a virus that is not going away,” Pardo said. “If we learn more ways to quickly regain the sense of smell, we may be able to reduce the damage that loss of smell can cause to cognitive problems in sensitive people.”