As recently as 1987, British coal mines used caged canaries to act as sentinels, warning miners of toxic gases. Birds are more sensitive to them than we are, so they can suffer before the gas reaches levels dangerous to humans, allowing miners to avoid evacuation and suffocation.
The sense of smell is the canary in the coal mine of human health, according to new research. A study published today in the journal PLOS ONE shows that losing your sense of smell is a good predictor of death within five years, suggesting that the nose knows when it’s dying, and that smell is a bellwether for a person’s overall state. as a marker of exposure to toxic substances in the body or environment.
The study included more than 3,000 participants aged 57 to 85 from the National Social Life, Health, and Aging Project (NSHAP), a longitudinal study of factors affecting well-being among older Americans.
In 2005-2006, Jayant Pinto of the University of Chicago and his colleagues asked all participants to perform a simple test to identify five common odors (rose, leather, fish, orange, and mint) using a number of misidentified odors. by odor severity score.
Five years later, the researchers wanted to identify as many participants as possible and conduct this odor test a second time. During the five-year interval between the two trials, 430 of the original participants died (12.5% of all participants). Of these, 39% of those who failed the first olfactory test died before the second test, compared to 19% of those with moderate loss of smell at the first test, and only 10% of those with a healthy sense of smell.
In other words, participants who failed the initial olfactory test were four times more likely to die within five years than those who correctly identified all five odors. This was true when controlling for other factors that affect smell, such as race, gender, mental illness, and socioeconomic status, and milder smell loss was associated with a slightly increased likelihood of impending death.
Loss of smell was a more accurate predictor of death than a diagnosis of cancer, heart failure, or lung disease, and the only common cause that predicted it more accurately was severe liver damage. But the researchers point out that this is unlikely to be the cause of death itself, arguing that it is only a sign of things to come, and offer two possible reasons why.
The olfactory nerve endings, which contain olfactory receptors, are the only part of the human nervous system that is continuously regenerated by primary cells. The production of new olfactory cells declines with age, as our ability to detect and distinguish odors gradually declines. Loss of smell indicates that the body is in a damaged state and is unable to repair itself.
The olfactory nerve is also the only part of the nervous system exposed to open air. Therefore, it allows poisons and pathogens to enter the brain more quickly, so loss of smell can be an early warning of something that will eventually lead to death.
Pinto and his colleagues did not examine the actual cause of death in the 430 participants, but said the information is important for further research into the link. The 3-minute smell test they used is less reliable than long-term clinical assessments, so they believe the link may be even stronger than their results suggest. They don’t know if the results apply to younger people, but if they do further testing, they may be able to quickly identify older people who are at risk.