While cognitive conditions like dementia and Alzheimer’s are often associated with older age, some risk factors—like ADHD and recurring nightmares—may be lifelong and thus diagnosed decades earlier. According to new research from Massachusetts General Hospital, however, there may also be a middle ground: certain early symptoms could signal cognitive decline 15 to 20 years before it begins.
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One such example? The loss of a particular sense—and no, it’s not vision (though that is another early predictor). This isn’t just a potential clue for early detection; it could also pave the way for earlier testing and intervention, which is exactly what this study set out to explore.
Published in Scientific Reports in March 2025, the study involved 127 cognitively healthy participants, 34 individuals who had noticed changes in their memory (but hadn’t received a diagnosis) and 19 people with mild cognitive impairment (MCI), a clinical condition often considered an early stage of Alzheimer’s disease.
As for which sense they were testing? Smell, since changes in the brain's ability to process odors may begin long before more obvious signs of cognitive decline, according to the researchers.
Each participant received a scratch-and-sniff test kit and was asked for odor identification (what smell it was), odor memory (if they had smelled it before or not) and odor discrimination (whether two scents were the same were different). They also ranked how strong each smell was on a scale from zero to 10.
The Connection Between Brain Health and Smell
The results? Older age was indeed linked to a decline in olfactory abilities, and especially especially in identifying and remembering odors. What's more, people with mild cognitive impairment (MCI)—which again, is considered an early stage of Alzheimer’s—demonstrated a "significantly worse performance" on smell tests than those without memory issues. This was especially the case for smell identification and discrimination, seemingly confirming the connection.
Finally, participants who had no sense of smell performed at "chance level," or demonstrated that they were guessing at random, confirming the test's accuracy.
According to the researchers, this research has tremendous potential for advancements in Alzheimer’s treatment—especially since early detection tends to equate with better prevention. “Early detection of cognitive impairment could help us identify people who are at risk of Alzheimer’s disease and intervene years before memory symptoms begin,” said senior author Dr. Mark Albers, MD, Ph.D., of the Laboratory of Olfactory Neurotranslation, the McCance Center for Brain Health, Department of Neurology at Massachusetts General Hospital and an assistant professor of neurology at Harvard Medical School.
“Our goal has been to develop and validate a cost-effective, noninvasive test that can be performed at home, helping to set the stage for advancing research and treatment for Alzheimer’s," he contined. Hopefully, this research will allow them to do just that.
Finally, this study proves that smell loss is not something to ignore. If you notice a gradual loss of smell, especially if you’re over the age of 55, it may be worth investigating or telling your doctor.
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Related: This Simple Habit May Be Quietly Raising Your Risk of Dementia and Alzheimer’s
Sources
"The AROMHA brain health test is a remote olfactory assessment to screen for cognitive impairment." Scientific Reports."Early detection of Alzheimer's may start with simple test." The Harvard Gazette. Read More Details
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