Lost your sense of smell? What does it mean?


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Lost your sense of smell? What does it mean?

A decreased sensitivity to smell is common as you get older, especially after the age of 70i. However, a moderate to complete loss of smell, known as anosmia, may predict an increased likelihood of death within five yearsii. Anosmia has been shown to be a much stronger predictor of mortality rates than other diseases such as heart failure, cancer or diabetesiii.

Anosmia is linked to a wide range of factors including physical trauma, viral infections, certain medications and exposure to environmental toxins such as pesticidesiv,v. New research from the University of Chicago shows anosmia can foreshadow a host of other health problems that patients may not be aware of yet, especially in older adults.

A moderate or complete loss of smell may indicate serious health concerns.

The research team initially surveyed 3,005 people aged 57 to 85 to determine whether or not they suffered from an impaired or lacking sense of smell, known as olfactory dysfunctionii. People who took part in the research were asked to correctly identify five common scents - rose, leather, orange, fish and peppermint. The participants were classified as "normosmic", having a normal sense of smell if they correctly identified at least four of the scents; "hyposmic", having a deficient sense of smell if they were able to correctly identify at least two of the scents; or "anosmic", having no sense of smell if they were unable to correctly identify at least one scent. Factors such as lifestyle, socioeconomic status, age group, and diseases such as heart failure, stroke or diabetes were also accounted for during the study. Five years after the initial survey, 430 of the respondents had passed away. The causes of death of the 430 people were not included in the study, however, the anosmic group had the most deaths, with 39 per cent of the total fatalities.

The study is not claiming that olfactory dysfunction is the primary factor in the increased mortality rates, but it does show that it is a strong predictor of death. Olfactory nerves have the ability to regenerate after physical trauma or sickness. Anosmia occurs when these nerves lose the ability to repair themselves, which can indicate a higher probability of an underlying condition impairing the ability for damaged nerves or tissues to regenerate later in lifeii.

The researchers who conducted the University of Chicago study recognised that their study, while comprehensive, does have its limitations and most likely underrepresents the association between anosmia and mortality.

What's in a smell?

The nasal and sinus cavities contain between 10 and 20 million olfactory neurons which bond to odour molecules from the airv. These neurons then send signals to the brain via the nervous system where the signals are processed as the scents that we recognise. However, much of the science behind how the sense of smell works remains unknowniv, such as how the brain distinguishes and identifies different scents.

Research has shown that scent plays a role in how we bond with and recognise family members.

What scientists do know is that the human sense of smell is directly related to a number of behavioural and physiological processes including memory, emotion and tasteiv. In fact, only 30 per cent of taste sensation comes from tastebudsiv. Odour molecules from the foods we eat contribute to the majority of what we taste, which is why foods often taste bland when we are sickiv. Even though the human sense of smell is significantly less developed than other mammals, it still plays an important role in how we interpret our environment, identify threats and to some degree, bond with and recognise friends and family membersiv.


iMedline Plus, Aging changes in the senses, viewed on 23 January 2014
http://www.nlm.nih.gov/medlineplus/ency/article/004013.htm

iiPinto, J et al 2014, "Olfactory dysfunction predicts 5-year mortality in older adults", PLoS One, ed. 107541, viewed on 4 November 2014,
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0107541

iii'The scent of death', The Economist, 4 October 2014, viewed 28 January 2015,
http://www.economist.com/news/science-and-technology/21621702-low-olfactory-acuity-portends-curtailed-lifespan-scent-death

ivState Government of Victoria, Anosmia - loss of smell, viewed on 4 November 2014,
http://www.betterhealth.vic.gov.au/bhcv2/bhcarticles.nsf/pages/Anosmia_loss_of_smell

vHarvey, R and Bou-Haider, P 2013, "Anosmia and parosmia", Australian Doctor, viewed on 5 November 2014,
http://www.australiandoctor.com.au/getmedia/247d536e-e25c-4e4b-9a78-47d416873e3c/HTT_027_034___18OCT_13.aspx