One of the stranger symptoms of Covid is the loss of the sense of smell – a symptom that was considered a warning sign for dementia even before the pandemic.
A big question for researchers now is whether the loss of smell associated with Covid could also be linked to cognitive decline. Around 5 percent of Covid patients worldwide – about 27 million people – have reported a loss of smell lasting more than six months.
New preliminary results, presented Sunday at the Alzheimer’s Association International Conference in San Diego, suggest that may be the link, but experts caution that more research is needed.
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Previous studies have found that some Covid patients develop cognitive impairment after infection. In a new study – not yet published in a peer-reviewed journal – Argentinian researchers have found that loss of smell during Covid can be a strong predictor of cognitive decline, regardless of the severity of the disease.
“Our data show that adults over 60 years of age are more likely to have post-Covid cognitive impairment if they have olfactory dysfunction, regardless of the severity of Covid,” said study author Gabriela Gonzalez-Aleman, professor. Pontificia Universidad Catolica in Buenos Aires, Argentina added that it is too early to say whether the cognitive impairment is permanent.
The study followed 766 adults between the ages of 55 and 95 for a year after infection. Almost 90 percent had a confirmed case of Covid, and all underwent regular physical, cognitive and neuropsychiatric tests within a year.
Two-thirds of patients had some cognitive impairment by the end of that year. Half of the participants had severe impairment.
The researchers did not have exact data on the patients’ cognitive function before they got infected with Covid to compare the results at the end, but they asked the families of the participants about their cognitive function before the infection and did not include the sick people. obvious cognitive impairment before the study.
Loss of smell is a well-established precursor to cognitive decline, according to Jonas Olofsson, a psychology professor at Stockholm University who studied the link between smell and dementia risk and was not involved in the new study. It’s also well established that Covid can cause permanent loss of smell, he said.
“The question is where these two lines of research intersect,” Olofsson said. “This study is very surprising, but the data I have seen so far does not allow us to draw any strong conclusions. “
According to Dr. “Loss of smell is a signal of an inflammatory response in the brain,” said Claire Sexton, senior director of research programs and outreach at the Alzheimer’s Association.
“We know that inflammation is part of the neurodegenerative process in diseases like Alzheimer’s,” Sexton said. But we need to study more deeply how they are connected.’
A separate study unrelated to Covid was published last Thursday in the journal Alzheimer’s & Dementia. Researchers at the University of Chicago have found that not only does a decline in the sense of smell predict the loss of cognitive function over time, but loss of the sense of smell can also be a warning sign of structural changes in brain regions important in Alzheimer’s disease. dementia.
Using data from Rush University’s Memory and Aging Project, researchers tracked the loss of smell in 515 older adults over the age of 22. They also measured the volume of gray matter in parts of the brain associated with dementia and smell.
They found that people whose sense of smell declined more quickly over time had smaller amounts of gray matter in both of these brain regions. The same was not the case in parts of the brain associated with vision, suggesting that the sense of smell has a unique connection to cognition through structural differences.
“Not only can changes in olfactory function over time predict the development of dementia, but it can also predict the size of important brain regions,” said study leader Dr. Jayant Pinto, director of rhinology and allergy at UChicago Medicine.
A “critical” odor for recognition
Covid is not the first virus to cause smell loss, but viral smell loss was rare before the pandemic, Pinto said. This means that scientists have only recently been able to conduct large-scale studies of how the virus’ loss of smell affects cognition.
“The sense of smell is very important for cognition, especially for the brain to receive information about the environment. If you block that communication channel with the brain, it’s going to suffer,” said Dr. Carlos Pardo, a professor of neurology at Johns Hopkins University who was not involved in either study.
But it remains unclear whether Covid-related olfactory loss leads to cognitive decline.
“It’s an open question — does SARS-CoV-2 damage the olfactory system cause problems not only in the olfactory system, but also in the brain itself?” – said the chick.
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According to Olofsson, the olfactory system—the parts of the brain associated with smell, including the olfactory bulb, the part of the brain that processes smell—connects to the parts of the brain that process memory. While it’s possible that Covid could damage the olfactory bulb and then cause brain damage around it, Olofsson said it’s unlikely.
“There are several other ways to connect these two things. The reason may be a pathology unrelated to the effect of Covid,” he said.
Or, Covid may exacerbate olfactory loss or cognitive decline that went unnoticed before infection, Olofsson said. Patients may have experienced some cognitive decline after contracting Covid or may have experienced some impairment of the olfactory system, making them more susceptible to Covid-related smell loss.
“The olfactory function may have been preserved despite the atrophy, but when Covid came, it took it away,” he said.
If it is found that covid loss of smell can lead to cognitive impairment, understanding the link could help doctors intervene early on smell loss and prevent cognitive decline in people at high risk.
“We’re dealing with an endemic circulation of a virus that hasn’t gone away,” Pardo said. “If we learn more ways to quickly restore smell, we can reduce the damage that loss of smell can cause with cognitive problems in sensitive people.”
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