Loss of smell is a warning sign of Alzheimer’s.  What if you lose your sense of smell due to Covid?

Loss of smell is a warning sign of Alzheimer’s. What if you lose your sense of smell due to Covid?

Loss of smell is a warning sign of Alzheimer’s.  What if you lose your sense of smell due to Covid?

One of the strangest symptoms of Covid – loss of smell – is a symptom that, well before the pandemic, was considered a warning sign for dementia.

The big question for researchers now is whether Covid-related loss of smell may also be associated with cognitive decline. About 5% of Covid patients worldwide, around 27 million people, have reported loss of smell for more than six months.

New preliminary results presented Sunday at the Alzheimer’s Association International Conference in San Diego suggest there may be a link, although experts warn that more research is needed.

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Previous research has found that some Covid patients develop cognitive impairment after infection. In the new study, which has not been published in a peer-reviewed journal, Argentine researchers found that loss of smell during Covid may be a stronger predictor of cognitive decline, regardless of the severity of the disease.

“Our data strongly suggest that adults over the age of 60 are more vulnerable to post-Covid cognitive impairment if they have smell dysfunction, regardless of the severity of Covid,” said study co-author Gabriela Gonzalez-Aleman. professor at Pontificia Universidad Catolica Argentina in Buenos Aires, adding that it is too early to tell if the cognitive impairment is permanent.

The study monitored 766 adults between the ages of 55 and 95 for one year after their infection. Nearly 90% have had a confirmed case of Covid, and all have completed regular physical, cognitive, and neuropsychiatric tests over the course of a year.

Two-thirds of the infected people had some kind of cognitive impairment at the end of that year. In half of the participants, the impairment was severe.

The researchers did not have hard data on the state of the patients ‘cognitive function before contracting Covid to compare them with the results at the end, but they asked the participants’ families about their cognitive function before the infection and did not include people who had clear cognitive impairment before the study.

According to Jonas Olofsson, a professor of psychology at Stockholm University who studies the link between the sense of smell and the risk of dementia, and was not involved in the new research, loss of smell is an established precursor of cognitive decline. It is also well known that Covid can lead to lasting loss of smell, he said.

“The question is whether these two lines of research intersect,” Olofsson said. “This study is quite tempting, even if the information I have seen so far does not allow for strong conclusions. “

The smell-brain connection

According to Dr. Claire Sexton, senior director of science and awareness programs at the Alzheimer’s Association, “loss of smell is a signal of an inflammatory response in the brain.”

“We know that inflammation is part of the neurodegenerative process in diseases like Alzheimer’s,” Sexton said. But we have to dig deeper into exactly how they are connected ”.

A separate, unrelated Covid study, published last Thursday in the journal Alzheimer’s & Dementia, investigates this connection further. Researchers at the University of Chicago found that not only can a decline in smell over time predict the loss of cognitive function, but the loss of smell can also be a warning sign of structural changes in brain regions important to Alzheimer’s disease and dementia.

Using data from Rush University’s Memory and Aging project, the researchers tracked loss of smell in 515 seniors over 22 years. They also measured the volume of gray matter in dementia-related and olfactory-related parts of the brain.

They found that people whose sense of smell decreased faster over time found themselves with smaller amounts of gray matter in both of these brain regions. The same was not true of vision-related parts of the brain, suggesting that smell has a unique link to cognition in terms of structural differences.

“Not only can the change in olfactory function over time predict the development of dementia, it can also predict the size of those brain regions that are important,” said study leader Dr Jayant Pinto, director of Rhinology and Allergy. at UChicago Medicine.

‘Critical’ smell for cognition

Covid is not the first virus to cause loss of smell, but virus-related loss of smell was a rare event prior to the pandemic, Pinto said. This means that scientists have only recently been able to conduct extensive studies on how the loss of smell caused by a virus can affect cognition.

“Smell is extremely critical for cognition, particularly for the brain to manage information about the environment. If you disrupt that communication channel with the brain, it will suffer,” said Dr. Carlos Pardo, professor of neurology at Johns Hopkins University, who was not involved in either study.

But it’s unclear whether Covid-related loss of smell can cause cognitive decline.

“This is an open question: does SARS-CoV-2 damage to the olfactory system cause problems not only in the olfactory system, but also in the brain itself?” Pinto said.

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According to Olofsson, the olfactory system – the parts of the brain related to smell, including the olfactory bulb, the part of the brain that processes smell – connects to the parts of the brain that process memory. Although it is possible that Covid disrupts the olfactory bulb and therefore the brain deteriorates around it, Olofsson said this is not likely.

“There are many other ways these two things can be related. The cause could be a disease not related to the Covid effect, “she said.

Or Covid could simply amplify existing loss of smell or cognitive decline that went unnoticed prior to the infection, Olofsson said. Patients may have already experienced some cognitive decline when they contracted Covid, or they may already have had mild impairment of the olfactory system, which made them more susceptible to Covid-related loss of smell.

“It may be that the olfactory function was maintained despite it being atrophied, but when Covid arrived it wiped out,” he said.

If it turns out that Covid loss of smell can cause cognitive impairment, understanding the connection could help doctors intervene early with the loss of smell and potentially prevent cognitive decline in high-risk people.

“We will deal with the endemic circulation of a virus that is not disappearing,” said Pardo. “If we learn more ways in which we are able to quickly recover our sense of smell, we may be able to minimize the damage that loss of smell can cause with cognitive problems in people who are sensitive.”

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