Loss of Smell May Be an Early Sign of Alzheimer’s Disease

May 26, 2022

A declining sense of smell may be an early sign of Alzheimer’s disease, a new report confirms. The study found that in some older adults, a loss of the ability to smell was tied to an increase in brain changes typical of Alzheimer’s disease. 

Researchers tracked 364 older men and women who were part of the Baltimore Longitudinal Study of Aging, a long-running study of seniors living in the Baltimore area. All were free of serious memory problems at the start of the study period. 

Over the next two-and-a-half years, the study participants underwent tests of their ability to detect a range of aromas. They also underwent memory assessments as well as PET scans of the brain, which allow doctors to identify the telltale beta-amyloid plaques and tau tangles of Alzheimer’s disease. 

During that time, about 5 percent of the study participants developed mild cognitive impairment, or MCI, a clinical stage marked by faltering memory that may eventually lead to full-blown Alzheimer’s disease.  

The researchers found that those who showed declines in the odor tests were more likely to develop MCI. They considered various risk factors associated with Alzheimer’s disease, including age, depression, whether participants smoked, and whether they carried the APOE-e4 gene. A decline in the sense of smell was independently linked to an increased risk of developing memory problems. 

PET scans revealed that people who were losing their sense of smell also had brain changes typical of Alzheimer’s disease. As the ability to smell declined, the numbers of plaques and tangles in areas of the brain critical for learning and the sense of smell rose. The study was published in the Journal of Alzheimer’s Disease, 

The findings confirm earlier research in people and animals showing that a declining sense of smell may be a sign of impending memory problems and an increased risk of developing Alzheimer’s disease. Some Alzheimer’s clinics now administer “sniff tests,” in which patients are asked to identify various odors like bananas, smoke, cloves or garlic. An impaired sense of smell may lead to more extensive follow-up tests to look for signs of Alzheimer’s. Some, but not all, people with Alzheimer’s also have a poor sense of smell and are unable to detect common odors like natural gas or roses. 

It’s important to note, however, that losing your sense of smell does not mean that you will ultimately develop Alzheimer’s disease. As many people are now aware, Covid may impair the sense of smell, and other viral infections may also have this effect. Medications, aging, head injuries or sinus conditions can also impair the ability to smell.  

If you detect changes in your ability to smell, your doctor can help determine potential causes. Changes in the sense of smell may help to detect Alzheimer’s at its earliest stages, when potential treatments may be most effective.  

By ALZinfo.org, The Alzheimer’s Information Site. Reviewed by Marc Flajolet, Ph.D., Fisher Center for Alzheimer’s Research Foundation at The Rockefeller University.  

Source: Qu Tian; Murat Bilgel; Abhay R. Moghekar; et al: “Olfaction, Cognitive Impairment, and PET Biomarkers in Community-Dwelling Older Adults.” Journal of Alzheimer’s Disease. April 5, 2022. National Institute on Aging, National Institutes of Health. 


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