When we think about dementia, memory loss typically comes to mind first. Forgotten names, misplaced keys, repeated questions — these are the signs most of us associate with cognitive decline. But emerging research reveals that one of the earliest indicators of dementia often appears years before memory problems become noticeable, and it has nothing to do with forgetting things.
This unexpected early warning sign relates to a change in sensory perception, specifically your sense of smell. A declining ability to identify common odors may signal the very earliest stages of neurodegeneration, offering a potential window for intervention long before more obvious cognitive symptoms develop.
The olfactory connection to brain health
Your sense of smell, while often underappreciated, is intimately connected to brain function in ways that other senses aren’t. The olfactory system has direct neural connections to the brain regions first affected by Alzheimer’s disease and other dementias, particularly the entorhinal cortex and hippocampus.
Unlike your other senses that pass through the thalamus (the brain’s relay station) before reaching the cerebral cortex, smell information travels directly to key memory and emotion centers. This direct pathway makes your sense of smell uniquely vulnerable to the earliest stages of neurodegeneration.
When protein abnormalities like tau tangles and amyloid plaques — hallmarks of Alzheimer’s disease — begin accumulating in the brain, they often appear in these olfactory-connected regions first, sometimes decades before clinical symptoms emerge. This explains why changes in smell function can precede memory problems by 5-10 years or more.
Beyond normal aging: When smell changes signal concern
Our sense of smell naturally declines somewhat with age, but the changes associated with early neurodegeneration are different in both pattern and severity. Normal age-related changes typically reduce smell sensitivity gradually, meaning you might need a stronger concentration of an odor to detect it.
The smell changes associated with early dementia are more specific, affecting your ability to identify and distinguish between different odors, even when you can detect something is present. This difference is crucial—many people with early neurodegeneration can still sense that an odor exists but increasingly struggle to recognize what that smell represents.
Research has demonstrated that difficulty identifying common scents like lemon, peppermint, or chocolate correlates significantly with higher risk for developing dementia later. Multiple studies have found that older adults who fail smell identification tests have a 2-5 times greater risk of developing dementia within the next 5 years compared to those with normal smell function.
The smell test that predicts cognitive decline
Standardized smell identification tests have become valuable tools for assessing dementia risk. Tests like the University of Pennsylvania Smell Identification Test (UPSIT) present various common odors, asking participants to identify each from multiple-choice options.
Performance on these tests has proven remarkably predictive of future cognitive decline. In one landmark study following nearly 1,400 cognitively normal older adults, those who couldn’t identify at least 34 out of 40 common odors had more than twice the risk of developing dementia within 5 years. Those who identified fewer than 30 had nearly five times the risk.
What makes this finding particularly significant is that these participants showed no memory problems or other cognitive symptoms at the time of testing. Their smell difficulties preceded detectable cognitive changes by years, potentially offering a crucial early warning.
Why most people miss this warning sign
Despite its predictive value, declining smell function typically goes unnoticed or unreported for several reasons. Unlike vision or hearing changes that immediately impact daily functioning, smell loss often occurs gradually enough that people adapt without realizing what they’ve lost.
Many people attribute declining smell to normal aging or sinus issues rather than considering it a potential neurological warning sign. Even when people do notice changes, they rarely mention them to healthcare providers, who traditionally haven’t included smell assessment in routine evaluations.
The social aspects of smell also contribute to its overlooked status. We rarely discuss how things smell in daily conversation, making it difficult to recognize when our perception differs from others. Without external validation, many people don’t realize their olfactory abilities are declining until the loss becomes severe.
Beyond Alzheimer’s: Smell changes in other dementias
While extensively studied in Alzheimer’s disease, smell dysfunction appears across various neurodegenerative conditions, albeit with different patterns. In Parkinson’s disease, smell loss is often more severe and occurs even earlier in the disease process, sometimes decades before motor symptoms develop.
In frontotemporal dementia, smell identification may remain relatively preserved early on while other smell processing abilities decline. Lewy body dementia typically shows intermediate smell impairment between Alzheimer’s and Parkinson’s patterns.
These varying patterns suggest that specific aspects of smell dysfunction might eventually help differentiate between types of neurodegeneration, potentially leading to earlier and more accurate diagnosis of different dementia subtypes.
When smell changes are accompanied by taste alterations
Because smell and taste are intimately connected sensory systems, changes in smell function often affect flavor perception. Many people with early neurodegeneration report that food “doesn’t taste the same” long before they recognize specific smell difficulties.
This flavor perception change can lead to altered eating habits that family members might notice. Increased preference for very sweet or highly spiced foods, sudden dislike of previously enjoyed dishes, or complaints about food tasting bland might reflect underlying neurological changes rather than simple preference shifts.
Weight loss often accompanies these changes, as eating becomes less pleasurable and appetite diminishes. Unexplained weight loss combined with complaints about food flavor changes represents a particularly concerning combination that warrants medical evaluation.
Other unusual early signs that accompany smell changes
While smell dysfunction can independently predict future cognitive decline, it rarely occurs in isolation. Other subtle changes typically develop in the same early timeframe, creating a constellation of symptoms that together suggest increased dementia risk.
Changes in sleep patterns, particularly reduced REM sleep or new sleep disturbances, often accompany early smell dysfunction. The brain regions involved in both smell processing and sleep regulation overlap significantly, with both affected by early neurodegeneration.
Subtle mood changes, especially increased anxiety or apathy, frequently develop alongside smell dysfunction. These aren’t typically severe enough to meet clinical criteria for depression or anxiety disorders but represent noticeable shifts from the person’s baseline emotional state.
Visual-spatial processing difficulties, like decreased ability to judge distances or navigate in familiar environments, sometimes emerge concurrently with smell changes. Together, these seemingly unrelated symptoms reflect the spreading pattern of early neurodegeneration affecting multiple brain regions.
What to do if you notice smell changes
If you or someone you care about experiences persistent changes in smell function, particularly difficulty identifying common odors, consider these steps:
- Consult a healthcare provider about smell assessment options. While not yet standard in most medical practices, formal smell testing can provide valuable information about potential neurological health.
- Rule out common non-neurological causes of smell dysfunction, including chronic sinus conditions, certain medications, smoking, and COVID-19 (which can cause temporary or sometimes persistent smell disturbances).
- Pay attention to other subtle changes that might accompany smell alterations, such as sleep disturbances, mood shifts, or minor difficulties with complex tasks that were previously effortless.
- Consider lifestyle modifications shown to support brain health and potentially slow neurodegeneration, including regular physical exercise, cognitive stimulation, social engagement, Mediterranean-style diet, quality sleep, and stress management.
- Explore opportunities to participate in research studies focused on early-stage neurodegeneration, which might provide access to advanced assessments and emerging interventions not yet available in standard clinical practice.
The hopeful side of early detection
While discovering potential early signs of neurodegeneration might seem frightening, early awareness creates valuable opportunities. The decades-long progression of conditions like Alzheimer’s disease means that interventions started at the earliest stages have the greatest potential to preserve cognitive function.
Emerging research suggests that multi-domain lifestyle interventions implemented at the first signs of neurodegeneration can significantly influence disease trajectory. Some studies indicate that aggressive management of modifiable risk factors might delay symptom progression by years or even decades in some individuals.
Additionally, pharmaceutical treatments being developed specifically for early-stage neurodegeneration show more promise than those targeting advanced disease. Clinical trials increasingly focus on presymptomatic or very early-stage participants, making early identification crucial for accessing cutting-edge treatments.
Understanding the link between smell function and brain health transforms an overlooked sense into a valuable monitor of neurological wellbeing. This knowledge doesn’t just offer earlier detection of potential problems—it provides motivation for brain-healthy lifestyle choices that benefit everyone, regardless of current cognitive status.
The next time you can’t quite place a familiar smell, consider it a reminder of how intricately your senses connect to your brain health. That strange symptom of smell dysfunction, while easy to dismiss, might be telling you something important about what’s happening in your brain years before more obvious signs appear—giving you the chance to take action when it matters most.
