The Instruments.
Your Senses Are Measuring You Back.
The five channels you experience the world through are also five readouts on the state of your nervous system. One of them predicts five-year mortality better than heart failure does. Another is the single largest modifiable risk factor for dementia. Two of them have treatments that work and are not being used.
We talk about the senses as if they were windows. Passive openings. Light comes in, sound comes in, and somewhere behind them the real business of being a person happens.
That framing is wrong in a way that has consequences. Each sense is an organ system with its own cells, its own turnover rate, its own ageing curve, and its own relationship to the brain. And because each one is wired into the brain differently, each one fails in a way that reports something specific about what is happening upstream.
The clearest example is smell, so let me put it plainly and then justify it for the rest of the post. In a study of three thousand older adults, the ones who could not identify basic odours at baseline were dead five years later at nearly four times the rate of those with normal smell. Anosmia predicted five-year mortality more strongly than heart failure, lung disease, or cancer did. [1]
Nobody thinks to test it. It costs almost nothing and takes about five minutes.
So this is a post about using your senses fully, in a more literal sense than that phrase usually gets. Not as an aesthetic instruction. As a set of instruments that report on the machine, some of which can be repaired, and most of which are being ignored.
Five Instruments, Five Clocks
Each sense declines on its own schedule and reports on something different. Tap through.
Every figure here comes from the numbered sources at the foot of the post. Where a claim is mechanism rather than measurement, it says so. [1][2][3][4][5][8]
Of the five, smell is the one that behaves least like the others, and the one worth understanding first.
The olfactory system is one of the very few places in the adult human nervous system where neurons are continuously replaced. Olfactory receptor neurons sit in the roof of the nasal cavity, exposed directly to the outside world, and they are regenerated from a stem cell population throughout life. That arrangement makes the sense of smell unusual: it is a neural tissue that depends on ongoing regeneration to keep working.
It also means that when smell fails, there are several quite different things it could be telling you.
The Five-Year Signal
3,005 adults aged 57 to 85, tested on five odours, followed for five years. Tap a group.
Pinto and colleagues, National Social Life, Health and Aging Project. Observational: smell loss predicted death, it did not cause it. [1]
Smell is the most striking finding. Hearing is the most actionable one, and the gap between those two facts is where this post turns from interesting to irritating.
Hearing loss is the largest single modifiable risk factor for dementia in the Lancet Commission's list. The 2024 update identifies fourteen modifiable risk factors that together account for around 45 percent of dementia cases worldwide. Hearing loss is assigned 7 percent of that total, one of the largest individual contributions, and vision loss was added as a risk factor in this update. [2]
The longitudinal data behind it. Frank Lin and colleagues followed 639 adults in the Baltimore Longitudinal Study of Aging for nearly twelve years. Compared with normal hearing, the risk of incident dementia rose with severity of baseline hearing loss: mild, moderate and severe hearing loss carried hazard ratios of 1.89, 3.00 and 4.94 respectively. [3]
And then somebody ran the trial. ACHIEVE randomised 977 adults aged 70 to 84 to a hearing intervention or a health education control and followed them for three years. In the study population as a whole, the primary result was negative: no significant difference in cognitive decline. In the subgroup recruited from an existing cardiovascular cohort, who had more risk factors and were declining faster to begin with, the hearing intervention was associated with a 48 percent slowing of three-year cognitive decline. [4]
What to do with a result like that is a real question rather than a rhetorical one. A prespecified subgroup showing a large effect in the people most at risk is not nothing. It is also exactly the shape a false positive takes. The honest reading is that hearing intervention looks promising in higher-risk older adults and has not been demonstrated in the general older population.
Vision has a similar story with a better piece of design in it. Cecilia Lee and colleagues followed 3,038 participants in the Adult Changes in Thought study and found that cataract extraction was associated with a lower risk of dementia, hazard ratio 0.71. [5]
The clever part is the control. If this were simply healthier people being more likely to have elective surgery, then any eye surgery should show the same protection. So they looked at glaucoma surgery, which does not restore vision in the same way. Hazard ratio 1.08, no association. [5] That does not prove causation. It does remove one of the two most obvious alternative explanations.
Restoring the input is associated with protecting the brain. Operating on the same organ without restoring the input is not. That is about as close to a mechanism as observational data gets.
What Can Actually Be Trained or Restored
Six interventions, sorted honestly. Filter by how good the evidence is.
Grades reflect study design and replication, not how much I like the intervention. [4][5][6][7][8]
Two things are true about women and the senses, and one of them is not what you would expect.
The first is unsurprising. A meta-analysis by Piotr Sorokowski and colleagues pooled studies of olfactory performance and found that women outperformed men across olfactory tasks, a difference that shows up consistently enough to be treated as real, though the authors are careful about its size. [9]
The second is stranger. Sharon Curhan and colleagues followed 80,972 women in the Nurses' Health Study II from 1991 to 2013 and looked at menopause, hormone therapy and hearing loss. Older age at natural menopause was associated with a higher risk of hearing loss, not a lower one. And longer duration of oral hormone therapy was associated with increasing risk. [10]
That runs against the intuition almost everyone brings to this, including me: more oestrogen for longer, better tissue, better hearing. The data did not say that. I am flagging it as one observational cohort rather than a settled result, and it is the kind of finding that should make anyone cautious about reasoning from what oestrogen ought to do to what it does.
Two of the fourteen dementia risk factors have a device sitting on a shelf that fixes them.
Most of the modifiable dementia risk factors are hard. Hypertension, diabetes, physical inactivity, air pollution, depression, education. Each one requires changing something large and slow about a life or a country.
Hearing loss and vision loss are different. The interventions are a hearing aid and a twenty-minute operation. They are among the best understood, most standardised procedures in medicine, and between them they account for a meaningful share of a 45 percent figure. [2]
And they are treated as optional. Hearing aids are widely uncovered or poorly covered, sold at consumer prices rather than dispensed as a treatment for an established risk factor. Sensory decline gets filed under things that happen to old people, alongside grey hair, rather than under things we intervene in. People wait years between noticing and acting, partly on cost and partly because nobody has told them it is a brain question rather than a volume question.
For women there is a second layer. Reporting a sensory change, especially one that comes with fatigue or brain fog in midlife, is an excellent way to be told it is hormonal and sent home. The Nurses' Health Study finding above exists precisely because somebody bothered to ask whether the hormonal story was true in a cohort large enough to answer it, and what came back was not the tidy answer. [10] Most women asking the same question in a consulting room do not get a cohort. They get the tidy answer.
If hearing loss is 7 percent of dementia worldwide, then a hearing test belongs in routine midlife care in the same way a blood pressure cuff does. It is not there. That is the thing worth being angry about.
Four things to hold lightly
The smell and mortality finding is observational and it establishes prediction, not cause. Losing your sense of smell does not kill you. It appears to be a signal from systems that are failing for other reasons, and the study cannot tell you which ones in any given person. [1]
The ACHIEVE trial's primary endpoint was negative. The 48 percent figure comes from one subgroup. Treat it as a reason to run the next trial in higher-risk people, not as an established treatment effect. [4]
Olfactory training has a real meta-analysis behind it, and its effects are measured on smell tests in people with smell disorders. It has not been shown to protect cognition, slow ageing, or do anything beyond improving olfactory function. Anyone extending it further is extending it past the data. [6][7]
And the hormone therapy and hearing association is a single observational cohort with self-reported hearing loss. It is interesting and it is not a reason to change anything about hormone therapy, which is a decision made on a completely different set of trade-offs and belongs with your doctor rather than with a blog post. [10]
Not when you start asking people to repeat themselves. Earlier, as a baseline, the way you would get a first blood pressure reading. Hearing loss at the mild end carries a measurable association with dementia risk, and mild is exactly the stage nobody notices. [3]
A sudden or progressive loss of smell with no obvious cause is worth mentioning to a doctor, because of what it can sit alongside rather than because of itself. This is one of the cheapest pieces of information about your nervous system available, and it is almost never collected. [1]
Cataract surgery is routinely deferred, framed as cosmetic, waited out. The ACT data suggests the deferral may not be neutral, and the glaucoma control makes the healthy-patient explanation less likely than it would otherwise be. [5]
Smell is the one sense with decent evidence that deliberate exposure improves function, and it was tested in people with measurable loss rather than as a wellness practice. [6][7] Everything else in this category, the slow eating, the walking without headphones, the touch that is slow rather than brisk, has good reasons and thin evidence. Do it because it is a better way to be awake, not because a study told you to.
The thing that stayed with me is not the mortality number, striking as it is. It is the asymmetry.
We have built enormous infrastructure around measuring things that are hard to measure and hard to change. Cholesterol panels, blood pressure, glucose. Meanwhile there are four or five instruments attached to every person's head, reporting continuously on the state of their nervous system, and we check them only when someone complains loudly enough.
And when they do fail, two of the failures have fixes that already exist, are already made, and are sitting behind a price tag and a cultural assumption that this is simply what getting older looks like.
So the instruction to use all your senses to the fullest turns out to be two instructions that got compressed into one. Pay attention with them, which is good for reasons nobody needs a citation for. And pay attention to them, which is a medical act that almost nobody performs.
The pattern in this post, that a system's decline gets read as inevitable ageing rather than as a treatable finding, and that women get told it is hormonal before anyone measures anything, is the pattern The Art of Female Health was written around. nammu.academy/book
References
- Pinto, J. M., Wroblewski, K. E., Kern, D. W., Schumm, L. P., & McClintock, M. K. (2014). Olfactory dysfunction predicts 5-year mortality in older adults. PLoS ONE, 9(10), e107541. https://doi.org/10.1371/journal.pone.0107541
- Livingston, G., Huntley, J., Liu, K. Y., et al. (2024). Dementia prevention, intervention, and care: 2024 report of the Lancet standing Commission. The Lancet, 404(10452), 572–628. https://doi.org/10.1016/S0140-6736(24)01296-0
- Lin, F. R., Metter, E. J., O’Brien, R. J., Resnick, S. M., Zonderman, A. B., & Ferrucci, L. (2011). Hearing loss and incident dementia. Archives of Neurology, 68(2), 214–220. https://doi.org/10.1001/archneurol.2010.362
- Lin, F. R., Pike, J. R., Albert, M. S., et al. (2023). Hearing intervention versus health education control to reduce cognitive decline in older adults with hearing loss in the USA (ACHIEVE): A multicentre, randomised controlled trial. The Lancet, 402(10404), 786–797. https://doi.org/10.1016/S0140-6736(23)01406-X
- Lee, C. S., Gibbons, L. E., Lee, A. Y., et al. (2022). Association between cataract extraction and development of dementia. JAMA Internal Medicine, 182(2), 134–141. https://doi.org/10.1001/jamainternmed.2021.6990
- Hummel, T., Rissom, K., Reden, J., Hahner, A., Weidenbecher, M., & Huttenbrink, K.-B. (2009). Effects of olfactory training in patients with olfactory loss. The Laryngoscope, 119(3), 496–499. https://doi.org/10.1002/lary.20101
- Sorokowska, A., Drechsler, E., Karwowski, M., & Hummel, T. (2017). Effects of olfactory training: A meta-analysis. Rhinology, 55(1), 17–26. https://doi.org/10.4193/Rhino16.195
- Löken, L. S., Wessberg, J., Morrison, I., McGlone, F., & Olausson, H. (2009). Coding of pleasant touch by unmyelinated afferents in humans. Nature Neuroscience, 12(5), 547–548. https://doi.org/10.1038/nn.2312
- Sorokowski, P., Karwowski, M., Misiak, M., et al. (2019). Sex differences in human olfaction: A meta-analysis. Frontiers in Psychology, 10, 242. https://doi.org/10.3389/fpsyg.2019.00242
- Curhan, S. G., Eliassen, A. H., Eavey, R. D., Wang, M., Lin, B. M., & Curhan, G. C. (2017). Menopause and postmenopausal hormone therapy and risk of hearing loss. Menopause, 24(9), 1049–1056. https://doi.org/10.1097/GME.0000000000000878