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Postgrad Med J. 2006 Apr; 82(966): 239–241.
PMCID: PMC2579627
Effects of ageing on smell and taste
This article has been cited by other articles in PMC.
Abstract
Disorders
of taste and smell commonly present diagnostic dilemmas to the medical
profession. This may be secondary to the lack of knowledge and
understanding of these conditions. There seems to be a low level of
interest in the disorders, when compared with disruption of the other
senses such as sight and hearing. Nevertheless, impairment of these
senses are common and may be life threatening, especially when they
involve the elderly patient. The aetiology of the conditions is
widespread, and extend beyond the content of this article. This article
will relate only to how the ageing process may contribute to sensory
dysfunction. It will focus on how the ageing process changes the normal
anatomy and physiology of the senses, how this effects the person's
quality of life, and the current management of these conditions.
Keywords: aged, olfaction disorders, taste disorders
The effects of ageing on smell
The sense of smell is often taken for granted, that is until it deteriorates. As we get older, our olfactory function declines.1,2
Not only do we lose our sense of smell, we lose our ability to
discriminate between smells. It has been reported that more than 75% of
people over the age of 80 years have evidence of major olfactory
impairment, and that olfaction declines considerably after the seventh
decade.1 A more recent study found that 62.5% of 80 to 97 year olds had an olfactory impairment.3 However, it is widely accepted that taste disorders are far less prevalent than olfactory losses with age.4
There
are numerous theories on why the sense of smell deteriorates as we age,
I shall attempt to outline a few of these. Various anatomical and
physiological theories have been presented. We are aware that both the
number of fibres in the olfactory bulb, along with olfactory receptors
decrease noticeably with age.1
The bulb losses may well be secondary to sensory cell loss in the
olfactory mucosa, along with a general deterioration in central nervous
system cognitive processing functions. Even in the absence of disease,
olfactory receptor neurones undergo apoptosis at a baseline rate in each
person. Mammals have the ability to replace these cells, however this
process degenerates with ageing.5
This results in a reduction in the surface area of olfactory
epithelium, along with reduced numbers of olfactory receptor neurones.
In addition, it is thought that age related olfactory dysfunction is
related to an increase in receptor cell death.2
Activation of the piriform/amygdalar region and the orbitofrontal
cortex has been shown to be reduced in older subjects when exposed to
stimulation.6
In some cases, olfactory loss may be secondary to age related
appositional bone growth resulting in the pinching off of the olfactory
fila as they traverse the ethmoid bone.7
Certain general diseases such as liver disease and non‐otolaryngological cancers seem to influence olfactory function.8
Another contributing factor when considering age related olfactory
deterioration is mild cognitive impairment and Alzheimer's disease.
Electrophysiological results of patients with Alzheimer's disease and
pre‐clinical Alzheimer's disease confirm olfactory dysfunction.9
The effects of ageing on taste
Gustatory
dysfunction may indeed be related to the normal ageing process.
However, in many cases, what is perceived as a taste defect is truly a
primary defect in olfaction. Other than smell dysfunction, the most
frequent causes of taste dysfunction are prior upper respiratory
infection, head injury, drug use, and idiopathic causes.10,11,12
Chewing problems associated with tooth loss and dentures can also
interfere with taste sensations, along with the reduction in saliva
production. When presenting to the clinician, older patients with
impaired taste should be thoroughly evaluated for oral and pharyngeal
disease such as candidiasis. One theory is that normal ageing produces
taste loss because of changes in taste cell membranes involving altered
function of ion channels and receptors.13 Taste bud loss is thought to contribute less to this problem with no relation between taste acuity and number of papillae.14
Rather than whole mouth gustatory dysfunction, regional deficits are
much more common. It has been reported that there is a higher prevalence
of localised losses on the tongue in elderly subjects than in young
subjects.4 Despite their wide prevalence, most elderly people are unaware of regional taste deficits.
Smell and taste disorders: the consequences
The
theory behind the deterioration of these senses in the elderly person
has been covered, however effects on the person's lifestyle along with
the dangers associated with such disorders needs to be considered. The
world is a different place without the sense of smell. Pleasant
experiences such as the smell of flowers in spring, the aroma of fresh
coffee, or even a Sunday roast are lost forever. Contrast this with the
smell of garlic on an acquaintance's breath cutting a conversation
short.
Unfortunately,
smell and taste disorders in the elderly person are commonly
overlooked, as they are not considered critical to life. However, this
may not be the case. Decreased smell function is a contributory factor
in the age related increases in accidental gas poisonings and explosions
that can endanger public safety. Decreased smell and taste results in
appetite suppression resulting in weight loss, malnutrition, impaired
immunity, and deterioration in medical conditions.1,4,15 Nutritional problems are an important sequelae from smell and taste disorders.17
It has been reported that the elderly person requires a twofold to
threefold higher concentration of salt to detect it in tomato soup.17 The tendency toward higher salt and sugar intake in the elderly diet can aggravate health hazardous conditions.18 When the sense of smell is decreased or distorted, disability and decreased quality of life are reported.19
In addition to these problems, such conditions may be responsible for a
high degree of anxiety and depression in the elderly person. Anxiety in
the inability to taste and enjoy food, and fears that the symptom is
indicative of an underlying disorder. There is also a higher incidence
of depression in those who develop anosmia.11
Investigation of smell and taste disorders
When
a patient presents with a problem with their smell and taste, it is
important to fully investigate the problem regardless of their age.
Investigation is focused on the possible causes of such disorders as
outlined in the box. This includes a detailed history and examination
that may often lead to the cause of the problem, as is the case with
local causes such as nasal polyposis.
More extensive
testing with haematological and biochemical investigations are
frequently required to discover the various nutritional and endocrine
causes of smell and taste disorders.21 Radiological investigation such as computed tomography is necessary to detect neurological causes for the disorder.
It
is only when other causes have been ruled out that the ageing process
may be suspected as the important contributor to a smell and taste
disorder.
Management of smell and taste disorders
When
a patient presents with such a disorder, they initially need
counselling and reassurance that they do not have a malignant disease or
infection. Once diminished smell is diagnosed, the goal of management
entails preventing injury related to this. Visual stimulating gas
detection devices are good for those with a gas stove, as the person may
not be able to smell gas leaks. Relatives or neighbours need closer
involvement to check for spoiled food that if eaten could lead to food
poisoning. People who have taste disorders may benefit from flavour
enhancement of their foods. Flavours are mixtures of odorant molecules
that can be extracted or blended from natural products, or synthesised
based on chromatographic and mass spectrographic analysis of natural
products. Flavour enhancers supplement, enhance, or modify the original
taste or aroma of a food but do not have a characteristic taste or aroma
of their own. Salt is the most widely used additive in flavour
enhancement, but others such as monosodium glutamate are also commonly
used. Flavour enhancement for the elderly and sick can improve food
palatability and acceptance, increase lymphocyte counts, reverse or slow
functional decline, and improve overall quality of life. It also has
the potential to compensate for anorexia.22
An additional study found that flavour enhancement for elderly
retirement home residents resulted in improved immune status as
determined by T and B cell levels and improved grip strength.22 Taste and odour stimulation has also been shown to increase the rate of salivary IgA in the elderly person.23
Summary
This
article has briefly summarised what is known about ageing and smell and
taste disorders. More research is required in this field, along with
increased awareness to discover new management options to benefit those
with these disorders.
Footnotes
This article is part of a series on ageing edited by Professor Chris Bulpitt.
Funding: none.
Conflicts of interest: none declared.
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