Covid and dementia are linked in devastating ways. As the former ripped through the population in 2020, almost 25 percent (18,420) of those who died also had Alzheimer’s disease or another disease that causes dementia. Now, a new study has found another association and it could have implications for broad swathes of the country.
The newly presented findings, which have not been published in a peer-reviewed journal, found that loss of smell during Covid may be a stronger predictor of cognitive decline, regardless of severity of disease.
The preliminary findings, which experts qualify more research is needed, was presented Sunday at the Alzheimer’s Association International Conference in San Diego.
“Our data strongly suggest that adults over 60 years of age are more vulnerable to cognitive impairment post-Covid if they had a smell dysfunction, regardless of the severity of the Covid,” said study co-author Gabriela Gonzalez-Aleman, a professor at Pontificia Universidad Catolica Argentina in Buenos Aires, adding that it’s too soon to tell if the cognitive impairment is permanent.
The study tracked 766 adults ages 55 to 95 for a year after their infection.
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Nearly 90 percent had a confirmed case of Covid and all completed regular physical, cognitive and neuropsychiatric tests over the course of one year.
Two thirds of those infected had some type of cognitive impairment at the end of that year. In half of the participants, the impairment was severe.
There are some limitations to the study. The researchers did not have hard data on the state of cognitive function of the patients before contracting Covid in order to compare with the findings at the end, but they did ask participants’ families about their cognitive function before infection and did not include people who had clear cognitive impairment before the study.
The link between Covid-induced loss of smell and dementia requires further investigation but evidence published elsewhere suggests it’s not a farfetched notion.
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Alzheimer’s, which is characterised by memory loss, is the most common cause of dementia.
For the study, the team tracked 364 participants from the Baltimore Longitudinal Study of Aging (BLSA) over an average period of about 2.5 years. The NIA-led BLSA is the longest running study of healthy ageing in America.
The participants were initially cognitively normal and given baseline cognitive and odour identification tests and PET scans, a type of brain imaging that can detect amyloid-beta and tau deposits associated with Alzheimer’s and related dementias.
Over the study period, 17 participants, or five percent of the total tracked, were diagnosed with mild cognitive impairment (MCI), of which 11 cases were associated with Alzheimer’s, three with vascular dementia, and one with frontotemporal dementia. Two were unspecified based on clinical characteristics.
The research team found that each point of lower odour identification test performance was associated with a 22 percent higher chance of developing MCI.
This relation remained similar even after the investigators adjusted for age, sex, race, education, olfactory test version, apolipoprotein E gene (APOE ε4) carrier status, smoking, elevated depressive symptoms, and vascular disease.
The PET brain scans of this subset of participants showed that lower olfactory scores were associated with higher levels of Alzheimer’s pathology in the brain, particularly in regions associated with the sense of smell, including parts of the orbital frontal cortex, and regions important to memory and learning, such as the temporal lobe.
Further, participants with greater olfactory decline over time had higher levels of amyloid and tau in some regions related to both smell and memory function.
Amyloid and tau are two main proteins thought to interfere with the communication between brain cells in certain dementias.
