Researchers have known for a number of years that people with Alzheimer’s dementia have a poorer sense of smell than persons without dementia. Not having a good sense of odors can reduce enjoyment of life because of the connection between odors and tastes, and it can also be dangerous if a person doesn’t smell smoke or a gas leak. We don’t realize how we process scents all day long and how this contributes to our orientation toward the world.
I remember reading a study a few years ago about a woman who had a brain tumor that destroyed her olfactory bulb. She talked about how disoriented she felt in her own home and in social situations. The sense of smell is so important and yet it is not studied nearing as much as vision and hearing. However, it is the only sense that remains active during sleep!
You have probably had many experiences like the one the French writer, Marcel Proust, described in his book, Remembrance of Things Past, when the odor of a madeleine awakened memories of his childhood. Does thesmell of pine trees bring back memories of being “up north” or do you associate the scent of certain perfumesand after-shaves with particular people? Olfaction is very closely connected to memory.
The connection between olfactory dysfunction and dementia is beginning to get more attention from researchers. A recent paper studied almost 3,000 adults ages 57-85 over a five year period to see whether the inability to identify particular scents was connected to later development of dementia. The researchers used“Sniffin’ Sticks” which are like pens with particular odors. Participants were exposed to an odor and then were given a multiple-choice test with four possible answers. The odors were peppermint, fish, orange, rose, and leather.
After five years, the researchers followed up with the group and found that almost all the people who could not identify any of the odors correctly five years earlier had dementia. Of those who could only identify one or two odors correctly, 80% had developed dementia.
What accounts for this connection? The researchers suggested that the neuropathology that underliesAlzheimer’s dementia (accumulation of amyloid plaques and neurofibrillary tau tangles) may start earlier inthe olfactory system than in the cortex. They offered other possibilities for problems with the olfactory system beginning earlier than related problems in the brain.
The practical implications are that this could be a low-cost, non-invasive screening procedure that primary care physicians could use to identify people at risk of developing dementia. If you know you are at greater risk, you might then change your diet, start exercising more, engage in cognitively stimulating activities, and stay in contact with friends and family members. The “sniff test” would not substitute for a thorough diagnostic work- up but it could indicate that a person should pursue additional testing.
Adams, D. R., Kern, D. W., Wroblewski, K., McClintock, M. K., Dale, W., & Pinto, J. M. (2018). Olfactory dysfunction predicts subsequent dementia in older U.S. adults. Journal of the American Geriatrics Society, 66, 140-144.