· Lee Chee Cheow, M.Sc. Dip CMP · Cognitive Health · 5 min read
Loss of Smell and Dementia: An Early Warning Sign Worth Knowing
A 12-year study following older adults found that losing your sense of smell alongside mild cognitive changes was linked to a dramatically faster path to dementia. Here is what the data actually shows.
Of all the early-onset dementia signs, loss of smell is probably the one people least expect. It sits alongside more familiar changes — misplacing items, losing track of dates, difficulty finding words — but smell loss is now considered one of the earliest detectable warning signs of Alzheimer’s disease, preceding memory symptoms by years in some cases.
The study: tracking smell loss and cognitive impairment over 12 years
A population-based study published in GeroScience in May 2025 followed older adults for up to 12 years, tracking two things separately and in combination: cognitive impairment with no dementia (CIND) and olfactory dysfunction (OD) — a reduced or absent sense of smell. The researchers then measured how each group’s “dementia-free survival” declined over time, essentially charting how quickly people in each category went on to develop dementia.
The pattern that emerged was striking. People with neither issue (the “unimpaired” group) had the slowest decline in dementia-free survival. People with isolated olfactory dysfunction alone had a moderately faster decline. But people with both mild cognitive impairment and olfactory dysfunction together saw their dementia-free survival probability drop the fastest of any group — falling below 25% by around year 12 to 13 of follow-up.
The study’s event data over time makes the same point. Looking at the number of dementia events recorded among participants at each follow-up point:
| Follow-up | Unimpaired | Isolated CIND | Isolated OD | CIND + OD |
|---|---|---|---|---|
| 3-year | 5 of 1,403 | 5 of 326 | 20 of 474 | 35 of 203 |
| 6-year | 18 of 1,164 | 11 of 244 | 23 of 336 | 16 of 106 |
| 9-year | 24 of 962 | 8 of 191 | 28 of 249 | 6 of 60 |
| 12-year | 28 of 852 | 7 of 157 | 21 of 175 | 4 of 42 |
Even accounting for the smaller sample sizes in the combined group, the trend is consistent across the follow-up periods: adding olfactory dysfunction to existing mild cognitive impairment was associated with a faster rate of progression to dementia than either factor alone.
Why smell loss might come before memory loss
The biological reasoning behind this finding relates to where in the brain early Alzheimer’s-related changes tend to appear. The structures involved in processing smell are closely connected to — and in some cases overlap with — regions involved in memory formation. If degenerative changes begin in or near these regions before they spread to areas more directly tied to memory, a decline in the ability to identify or distinguish smells could plausibly show up on testing before memory symptoms become noticeable to the person or their family.
This is consistent with why researchers describe smell loss as a potential early marker rather than a symptom in its own right that “causes” further decline — it is a signal that may reflect changes already under way elsewhere in the brain.
What this does — and does not — mean for you
It is worth being precise about what this research supports and what it does not. A single episode of a blocked nose, a cold, or age-related dulling of smell is common and does not indicate dementia risk. The research described above is about a pattern — objectively measured olfactory dysfunction, generally identified through smell testing, occurring alongside other signs of mild cognitive impairment, tracked over many years in a large study population.
In other words, smell loss on its own is not a diagnosis, and it is not something to become alarmed about after one instance of “food tasting different.” But as part of a broader picture — particularly if it appears alongside other early warning signs such as increasing confusion, word-finding difficulty, or disorientation — it is a legitimate data point that clinicians and researchers are increasingly paying attention to.
Frequently asked questions
Does losing my sense of smell mean I have dementia? No. Smell can be affected by many common, unrelated causes — sinus issues, colds, medications, ageing, or nasal injuries. The research above is about smell loss measured formally and tracked over years alongside other cognitive signs, not a single instance of reduced smell.
How much earlier can smell loss appear compared to memory symptoms? Research describes smell loss as potentially preceding memory symptoms “by years,” though the exact timeline varies between individuals and studies. It is best understood as an early signal worth noting rather than a precise countdown.
Should I get a smell test if I’m worried about dementia risk? If you are also noticing other early warning signs — memory lapses that interfere with daily life, disorientation, or word-finding difficulty — it is worth discussing all of these with a doctor together, rather than focusing on smell testing in isolation.
What made the combined CIND + OD group different in this study? The study found that having both mild cognitive impairment and olfactory dysfunction together was associated with a substantially faster decline in dementia-free survival than either factor alone, suggesting the two together may be a stronger signal than each considered separately.
This article is for general information only and does not constitute medical advice. If you have noticed changes in your sense of smell alongside memory or thinking changes, consult a doctor for a proper assessment.