A sudden loss of smell could signify a larger problem, according to new research. The connection between smell and memory is strong, but a decline in your sense of smell can not only predict waning cognitive function but also signal changes in areas of the brain involved in dementia and specifically Alzheimer’s.
Changes in the brain with loss of smell
University of Chicago researchers discovered that a rapidly failing sense of smell could come just before a similar decline in cognition, as well as other known facets of Alzheimer’s disease and dementia—such as the shrinking of gray matter in parts of the brain dedicated to smelling and memory.
“We were able to show that the volume and shape of gray 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,” Dr. Jayant M. Pinto, MD, senior researcher for the study, told Neuroscience News.
Researchers were able to see neurodegeneration in subjects with the most severe olfactory decline via MRI. Those whose sense of smell decreased the fastest saw the biggest cognitive declines, with the connection between loss of smell and cognitive changes being stronger the younger a subject was when that sense began to break down.
This research could lead to new, affordable screenings for dementia and Alzheimer’s that might be able to predict a person’s risk long before they experience cognitive decline. Such smell tests could result in earlier intervention and therefore slow that decline.
This research could lead to new, affordable screenings for dementia and Alzheimer’s that might be able to predict a person’s risk long before they experience cognitive decline.
The link between smell and memory
So how are cognition and sense of smell connected anyway? It has to do with their proximity to each other in the brain. The olfactory bulb – which processes smells – sits right up front, passing data on to the limbic system. The limbic system uses that information to activate the parts of the brain involved in learning, memories and emotions, often acting as the impetus for some sort of action. For example, waking up to the smell of gas or smoke should elicit a feeling of danger and perhaps a desire to escape. Likewise, encountering the perfume or cologne a lost loved one used to wear might bring on overwhelming feelings of longing or sadness.
Recognizing smells is a function of memory, so it makes sense that losing one might tell us something about losing the other. Interestingly, the structural changes that occur with Alzheimer’s disease can be found not just in regions of the brain related to memory, but in olfactory regions as well.
What about COVID-19-induced loss of smell?
If you or someone you care for is one of the 15 million people around the world who have not regained their sense of smell after recovering from the coronavirus, you might be worried about potential long-term effects on cognition.
“This is a major question,” Pinto said. “We don’t know if injury to the olfactory nerve from viruses will cause brain problems in the future. But the loss of olfactory input could potentially be harmful to the brain (it certainly is to quality of life). We also don’t know if some of the brain effects from COVID are direct (injury to the brain itself from the virus) or indirect (due to effects on blood supply, the immune system, from being in the ICU, etc). The olfactory nerve is however a potential conduit for viruses to reach the brain. Our study did not address these issues, but shows rapid loss has consequences for brain structure in the context of aging. And that may be important for AD.”
Leslie M. Kay, PhD, the author of a recent study on the topic, shares this concern as she told Neuroscience News:
“The review offers evidence that suggests inflammation introduced to the olfactory nerve and damage to the olfactory bulb via COVID-19 infection and immune response may also cause degeneration of brain structures connected to the olfactory system and cognitive impairment.”
Likewise, Gabriela Gonzalez-Aleman, a professor at Pontificia Universidad Catolica Argentina conducted a study that demonstrated a connection between cognitive decline and loss of smell after recovering from COVID and shared her opinion with NBC News:
“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.”
What we know about COVID-19 and loss of smell
- About 80 to 90% of people who test positive will experience at least some loss of smell.
- This symptom generally kicks in on the fourth or fifth day of illness, but this can vary.
- Most people recover their sense of smell within a week or two.
- A total of 16% took longer than six months.
- About 12% are estimated to have an ongoing issue with their sense of smell.
- Seniors have more than double the risk for long-term loss of smell.
What can caregivers do?
Loss of smell is one of the earliest and most often overlooked symptoms of Alzheimer’s and dementia. Early intervention means that treatments can begin sooner, which could delay some cognitive loss and put the family in a better position to plan for the future. Caregivers can also be better prepared for what’s to come.
There are also possible fixes for a decline in a sense of smell that might be worth trying. Smell training has been shown to help elderly people restore not only which odors they can identify, but some of their cognition as well. The training consists of sniffing a series of at least four strong scents multiple times per day. Recommended fragrances include:
Surgery is another possible option as it can restore a sense of smell lost to nasal polyps—along with eliminating other symptoms of chronic allergies. Even more impressive, researchers noted that polyp removal was associated with improved cognition. For seniors who don’t require surgery but tolerate nasal irrigation, a neti pot can help by removing built-up allergens and mucus so they can breathe – and smell – freely once again.