Sniffing out good health
Losing your sense of smell has been added to the list of Covid-19 symptoms that should prompt people to self-isolate. Jane Symons reveals how the sense we think about least has a profound impact on physical and mental health
Whether it’s newly mown grass, freshly brewed coffee or the lavender scent a much-loved grandmother used to wear, there are aromas that instantly transport us to another time and place.
Compared to our other senses, such as sight or hearing, the sense of smell is probably the one we think about least. Yet our ability to smell – and what odours we can identify – has a big impact on our health and wellbeing.
The importance of smell has been pushed into the spotlight by Covid-19. As the coronavirus began to spread, doctors were puzzled that so many patients were saying they had lost their sense of smell.
Similar stories were shared on social media. By March, ear, nose and throat specialists were advising that anosmia (the medical term for losing your sense of smell) should be added to the list of Covid-19 symptoms.
UNIQUE
Professor Vincent Deary, an olfactory expert based at Northumbria University says: “What is unique is that the smell loss occurs early in the infection and there is no nasal obstruction, so it could be a really important marker of Covid-19.”
This was brought home to him when his sister, a community nurse, mentioned that both she and her husband had lost their sense of smell. Professor Deary warned his sister it might mean they had Covid-19, so she and her husband played safe and self isolated. A few days later, both developed a fever and cough and were diagnosed with the coronavirus.
As Professor Deary points out: “If it hadn’t been for that chance conversation, my sister would have continued to work and could have passed the infection on to so many vulnerable patients.”
The association between aromas and our physical and mental health can be explained by anatomy says Professor Nancy Rawson, a cellular neurobiologist based at the Monell Chemical Senses Centre in Philadelphia.
She says: “Our sense of smell is directly connected to the parts of our brain associated with memory and emotion.
“Odours activate receptors in the olfactory bulb, a structure near the bridge of the nose, which is only two connections away from the hippocampus and the amygdala – the learning and memory parts of the brain.”
Scientists recently discovered that these olfactory receptors – once thought to be only related to smell – are also found in almost every part of the body including the heart, lungs, gut, skin and sperm. And they are now known to influence a range of crucial functions including blood pressure, breathing, blood sugar levels and wound healing.
Mind the scent
Our ability to recognise smells fades as we get older, in much the same way that our sight and hearing deteriorate with age, but it can also be an early sign of dementia and other neural disorders.
A study involving 3,000 adults, aged 57 to 80, found that 80% of those who could not identify at least two of five distinct odours – peppermint, fish, orange, rose and leather – were diagnosed with dementia within five years.
Lead researcher Professor Jayant Pinto, from the University of Chicago, says: “Loss of the sense of smell is a strong signal that something has gone wrong and significant damage has been done to the brain.
“A simple smell test could provide a quick and inexpensive way to identify those who are at high risk.”
There is an even stronger connection with Parkinson’s disease. The combined data from seven large studies showed the loss of smell almost quadruples the risk of developing the condition.
The nose knows
Scientists at the University of Manchester found that some people can also sniff out Parkinson’s disease before there is any hint of a problem.
The discovery came when Joy Milne, an ex-nurse, attended a patient support
By sniffing T-shirts, she identified the ones worn by people with Parkinson’s
group and noticed the other Parkinson’s sufferers had the same distinctive smell her husband Les had developed 12 years before his diagnosis.
Researchers confirmed Joy was right by having her sniff T-shirts worn by both healthy people and those with Parkin- son’s. She identified every one of the shirts worn by the Parkinson’s patients, and said one from the healthy control group had the same smell. Eight months later, the wearer was diagnosed with Parkinson’s.
Diabetes can also be spotted through a sniff test. Sweet, slightly fruity smelling urine is a sign of poorly controlled blood sugar levels. But scientists believe the pong many people notice after eating asparagus is a harmless quirk of genetics.
Detection dogs
Dogs are even better disease detectives as they have smell receptors that are 10,000 times more accurate than ours. A study published last year showed they can be trained to detect blood samples from people with cancer with 97% accuracy.
An earlier trial at Amersham Hospital in Buckinghamshire showed that dogs can be trained to identify urine samples from patients with bladder cancer. And there are dozens of reports in medical journals of cancers being diagnosed because a family pet refused to leave someone’s side or kept licking their
owner.
Smell cells
When the olfactory receptors we use to detect smells are found in high numbers in other parts of the body, it can be a clue to cancer. Researchers from Dresden University discovered there are much higher concentrations of these scent cells in prostate cancer samples than there are in healthy tissue.
Love is in the air
Smells are an essential element of the bond between mother and child; babies can recognise their mother’s smell and trials confirm mothers are so tuned into the scent of their infants they can identify which clothes they have worn.
Brain imaging confirms the scent of their baby activates dopamine pathways, which are linked to reward, in a mother’s brain.
Studies have also shown that a women’s natural scent changes around the time they ovulate and this makes them more attractive to men.
Olfactory bulb moment
It’s common for people suffering from depression to lose their sense of smell and brain scans confirm that the olfactory bulb of people with a history of mood problems is, on average, 15% smaller than normal.
However, this offers a solution, too. Thomas Hummel, the expert in chemosensory systems at Dresden University, who made the discovery, says: “If you expose yourself to odours in a regular way, for four or five minutes twice a day, your sense of smell will improve and this will lead to a slight improvement in depressive symptoms.”
Con-scent-ration
Dr Chris Etheridge, a research chemist and medical herbalist, says the impact that smells can have on brain activity explains why essential oils can alter mood. “Rosemary and basil both have a stimulating effect on areas of the brain associated with learning and memory,” he says.
Trials at Northumbria University confirmed that when school pupils aged 10 and 11 worked in a room scented with rosemary oil, their scores on memory tests improved by up to 7%. A similar study in slightly older children confirmed exposure to rosemary oil also improved memory and concentration across a range of tests.
Scent to sleep
Lavender has long been recognised as a soothing scent, and Dr Etheridge says a number of studies confirm its effectiveness as a sleep aid.
One, which measured brain activity of volunteers who stayed overnight in a sleep laboratory, showed lavender oil increased deep, slow-wave, sleep. Another, published in the American Journal of Critical Care, found that when a small bottle of lavender oil was placed beside patients’ beds it reduced their blood pressure and improved the duration and quality of sleep.
Lavender is a key ingredient in Puressentiel’s Rest & Relax spray, which has been clinically proven to improve sleep. Sleep duration was increased by an average of 21 minutes after just four weeks and quality of sleep improved by 18%.
Volunteers woke feeling more energised and refreshed, and, at the end of the trial, there were no reports of rebound insomnia – a common side-effect of prescription medicines.