News · Brain & Mental Health
Thinking your smell has faded tracked depression best
Pooling 187,056 people across 23 studies, researchers in JAMA Otolaryngology found that people who felt their sense of smell had declined were more likely to be depressed, while measured smell loss showed a weaker and less stable link.
Based on a peer-reviewed systematic review and meta-analysis in JAMA Otolaryngology-Head & Neck Surgery
- 23 studies and 17 independent cohorts, covering 187,056 people at a mean age of 63.6.
- People who felt their smell had declined had 1.56 times the odds of depression (95% CI, 1.19-2.05).
- That held in the lowest-bias studies, across age groups, and for both ways of measuring depression.
- Measured smell loss started at 1.26 but fell to 1.12 once publication bias was corrected for.
- The corrected range for measured loss includes no effect at all, so only the perception held up.
Most people lose some ability to taste and smell as they get older, and most of them never mention it to anyone. A new synthesis in the journal JAMA Otolaryngology suggests that whether they notice may matter more for their mood than whether it is actually happening.
The team pooled 23 studies representing 17 independent cohorts, covering 187,056 individuals at a mean age of 63.6 years. They then did something most reviews of this question have not: they kept the two kinds of smell loss apart.
Two ways of losing your sense of smell
One is what a test finds. The other is what you notice. Researchers call them objective and subjective olfactory impairment, and they overlap far less than intuition suggests.
The distinction is easy to underrate. People with smell disorders may lose their sense of smell, or things may smell different, and both versions are common with age. But a laboratory odor-identification score and a person’s own sense that something has dimmed are separate measurements, and this analysis found they behave separately too.
What people noticed tracked with depression
Subjective smell loss was associated with depression across the 7 studies that could be pooled independently, at 1.56 times the odds.
That association did not fall apart under pressure. It remained robust in low risk of bias studies, where the estimate actually rose, and held across age groups, and for subjective and objective depression. The last part matters most: the link survived even when depression was established by clinical assessment rather than self-report, which rules out the simplest explanation that gloomy people simply answer every question gloomily.
What tests measured mostly did not
The objective side is where the story turns.
Measured smell loss showed an association with objective depression across the 11 studies at 1.26 times the odds, a weaker signal to begin with.
Then the authors did the check that most reports skip. Studies finding nothing are published less often than studies finding something, which inflates any pooled estimate. Correcting for that, the association attenuated after publication bias adjustment to 1.12, and the plausible range now runs from below no effect to above it.
An estimate whose range includes no effect is not a finding. It is a result that has failed to establish itself.
Two exceptions survived. It remained robust in older adults and individuals with anosmia, meaning people aged 65 and over and people whose sense of smell has gone entirely rather than partly.
Why perception might beat measurement
There is a tidy explanation, and the authors offer it carefully. The subjective link likely reflects negative self-perception and/or the evaluation of one’s own olfactory decline rather than comparison with population norms.
Put plainly: what appears to matter is registering a loss in yourself. A test result you never see cannot make you feel diminished. The private observation that food has stopped tasting of much can.
That reading also fits which groups held up on the objective side. Total loss and advanced age are the circumstances where a measured deficit is most likely to be noticed by the person carrying it.
What a pooled analysis of snapshots cannot settle
Direction is the central unknown. Most of the underlying evidence measured mood and smell at the same moment, so nothing establishes which came first. Depression flattens appetite and interest, and a person in the middle of it may report faded smell for reasons that have nothing to do with their nose.
The pooled studies also disagreed with each other considerably, which is expected when combining different populations, odor tests and depression instruments, and which widens the honest uncertainty around every number here.
The authors close on exactly that note, calling for longitudinal and mechanistic studies to sort out causal pathways.
What it is good for
Smell is not a trivial sense to lose. Taste and smell protect us, letting us know when food has gone bad or when there is a gas leak, and they make us want to eat, ensuring we get the nutrition we need.
The useful takeaway is smaller than a screening test and more human than one. When an older person mentions that things have stopped smelling like they used to, that sentence appears to carry information about how they are doing, whatever a laboratory would say about their nose.
People also ask
What is the difference between subjective and objective smell loss?
Subjective means you report that your sense of smell has faded. Objective means a test says so, usually by asking you to identify or detect standard odors. The two agree less often than people expect. Plenty of individuals who fail a smell test report no problem at all, and plenty who report a problem test normally.
So does smell loss cause depression, or the reverse?
This cannot say. Most of the pooled evidence is cross-sectional, meaning smell and mood were measured at the same moment. Depression itself dulls interest in food and blunts self-assessment, so it could easily produce a report of faded smell. The authors call explicitly for longitudinal and mechanistic studies to clarify causal pathways.
Why would the perception matter more than the measurement?
The authors suggest the subjective link likely reflects negative self-perception and the evaluation of one's own olfactory decline, rather than comparison with population norms. Noticing that something about you has diminished is a different psychological event from scoring below average on a test you never took.
Was the measured link real at all?
Partly, and in specific groups. The pooled association for measured loss was 1.26 times the odds, but adjusting for publication bias pulled it to 1.12 with a range that includes no effect. It stayed more robust in adults aged 65 and over and in people with anosmia, meaning a complete loss of smell rather than a partial one.
Should smell testing be used to screen for depression?
Not on this evidence. The authors say clinicians should be aware of the observed associations, although their clinical implications remain to be further established. That is a long way short of a screening recommendation, and this is general information rather than medical advice.