is loss of smell a sign of alzheimer's?

recent study linking loss of smell with brain diseases raises questions about covid-related side effects.

by dave yasvinski

published aug 02, 2022

4 minute read

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4 minute read

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loss of smell could be a sign of brain disease

a research team found that a rapid decline in one’s sense of smell during a period of normal cognition is, in fact, a predictor of multiple aspects of alzheimer’s disease. getty

a rapid decline in a person’s ability to smell not only predicts an impending loss of cognitive function, it may also indicate structural changes in areas of the brain associated with dementia and alzheimer’s disease, according to a new study. the research, published in alzheimer’s & dementia: the journal of the alzheimer’s association, may eventually lead to the creation of smell-test screening to assist in the earlier detection of alzheimer’s and other forms of cognitive impairment. “this study provides another clue to how a rapid decline in the sense of smell is a really good indicator of what’s going to end up structurally occurring in specific regions of the brain,” said jayant m. pinto, senior author of the study and a professor of surgery at the university of chicago.

alzheimer’s disease is a chronic condition that is believed to be the result of the accumulation of certain proteins in the brain that leads to the slow death of neurons, according to the alzheimer’s association. this process eventually produces symptoms of memory loss, difficulty thinking or changes in mood and behaviour. the disease is the most common cause of dementia, accounting for 60 to 80 per cent of all cases, and more than 747,000 canadians are currently living with alzheimer’s or another form of dementia. roughly 65 per cent of people diagnosed with the disease after the age of 65 are women.

researchers have long been aware of a link between dementia and one’s sense of smell because of the key role memory plays in our ability to recognize certain odours. the plaques and tangles that form in the tissues of people with alzheimer’s disease usually appear in areas of the brain associated with olfactory and memory before spreading to other regions, but it isn’t clear whether or not this damage is what compromises a person’s ability to smell.

the study comes at an interesting time as scientists study the covid-related loss of smell — according to nbc news, five percent of covid patients worldwide, which amounts to about 27 million people, have reported loss of smell lasting more than six months. it’s been found that some covid patients go on to develop cognitive issues after infection, nbc reports, noting that researchers caution that more research is needed.

does loss of smell mean you have alzheimer’s?

the university of chicago team set out to discover if it was possible to detect alterations in the brain that correlate to the loss of smell and cognitive function.

“our idea was that people with a rapidly declining sense of smell over time would be in worse shape — and more likely to have brain problems and even alzheimer’s itself — than people who were slowly declining or maintaining a normal sense of smell,” said rachel pacyna, lead author of the study and a fourth-year medical student at the university of chicago pritzker school of medicine.

by studying anonymous patient data contained in the rush university memory and aging project (map), a study group tested annually for, among other things, their ability to identify certain smells, the team found that a rapid decline in one’s sense of smell during a period of normal cognition is, in fact, a predictor of multiple aspects of alzheimer’s disease. this includes smaller gray matter volume in regions of the brain that deal with smell and memory, poorer cognition and a higher risk of dementia. the rapid loss of smell was found to be as significant to the development of alzheimer’s as carrying the apoe-e4 gene, the strongest known risk factor for the disease.

“we were able to show that the volume and shape of grey matter in olfactory and memory-associated areas of the brains of people with rapid decline in their sense of smell were smaller compared to people who had less severe olfactory decline,” pinto said.

one limitation of the study was that participants had only been given one mri scan, making it difficult to determine when structural changes in the brain actually began. as most participants were white, more work needs to be done to confirm if other populations are similarly affected.

still the team hopes that they will soon be able to explore the value of testing a patient’s sense of smell in clinics — similar to hearing and eye tests — as a way to provide early warning of impending cognitive impairment.

“we have to take our study in the context of all of the risk factors that we know about alzheimer’s, including the effects of diet and exercise,” pinto said. “sense of smell and change in the sense of smell should be one important component in the context of an array of factors that we believe affect the brain in health and ageing.”

dave yasvinski is a writer with healthing.ca

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