101 Facts About Ageing #22: The Ageing Sense of Smell

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As Daniel Patrick Moynihan, an American sociologist, politician, and diplomat once said: “Everyone is entitled to his own opinion, but not his own facts”. And we wholeheartedly agree. A shared set of facts is the first step to building a better world with longevity for all. In that spirit, we are creating a series that covers 101 indisputable facts about ageing, health and longevity.

Sense of smell (olfaction) declines with age, with the most common manifestation being a loss of sensitivity and ability to identify different odours. Odour identification usually remains relatively stable until the age of 50-60, after which a steep decline occurs. Females usually retain better olfactory sensitivity compared with males. Over the age of 85, 40% of men and 26% of women are anosmic (they have no sense of smell at all).

University of Pennsylvania Smell Identification (UPSIT) scores as a function of age and sex. In this test, subjects are tasked with identifying the smell of 10 odorants from a list of alternatives.
Doty and colleagues.17 Copyright 1984 American Association for the Advancement of Science.
Source

Our knowledge of how the olfactory system ages in humans is quite sparse. Changes in olfaction with age are thought to be the result of many factors, involving both the olfactory receptors that convert chemical signals into electrical impulses, and the processing of these impulses by the brain. In rodents, the number of olfactory receptors in the nasal cavity decreases with age, as may the number of synapses connecting these cells to those in the olfactory bulb in the forebrain. Loss of cells in regions of the cortex involved in olfactory processing may also occur.

The importance of sense of smell when it comes to quality of life is often neglected. Smell is, of course, necessary for a a correctly functioning sense of taste, the loss of which may lead elderly people to become disinterested in food. Loss of smell makes it harder to detect dangers such as gas leakages, fires and and spoiled foods. Interestingly, much like hearing loss, olfactory deficits are associated with memory loss and the development of neurological diseases including Alzheimer’s and Parkinson’s. In some cases, olfactory dysfunction may precede the onset of classic symptoms of these diseases by years or even decades.