by Dementia can be accurately predicted five years before symptoms develop with a simple smell test, according to recent research. A study of nearly 3,000 elderly people found that those unable to identify at least four out of five common smells were more than twice as likely to develop the disease.
And the more they smell, the greater the risk, the scientists said. The aromas in order of increasing difficulty were peppermint, fish, orange, rose and leather and could be used as an early warning system.
This would make drugs and lifestyle changes, such as a healthy diet and more exercise, more effective before the condition becomes destructive. The findings add to growing evidence that the first damage to the brain occurs in olfactory neurons, which distinguish between different aromas.
Five years after the initial test, almost all participants, aged between 57 and 85, who could not name a single smell, were diagnosed with dementia. And almost 80 percent of those who only gave one or two correct answers did as well.
Overall, there was a significant link between the amount of smell and the frequency of the disease. Professor Jayant Pinto, of the University of Chicago, said: “Our test just makes someone pay closer attention.
“A lot more work would need to be done to make it a clinical trial. But it could help find people who are at risk. Then we could enroll them in early-stage prevention trials.
“Of all the human senses, smell is the most undervalued and overlooked – until it’s gone. These findings show that smell is closely related to brain function and health, “
“We think that the ability to smell specifically, but also wider sensory function, could be an important early sign, making people more at risk for dementia.”
Almost eight out of ten (78%) of those were normal, and at least four out of five smells were correctly identified. But 14 per cent could only name three, five per cent two, two per cent one – and one per cent could not smell a single smell.
The ear, nose and throat surgeon who studies the genetics and treatment of olfactory and sinus disease said: “We need to understand the underlying mechanisms, so we can understand neurodegenerative disease and hopefully new treatments and interventions develop preventive measures.
“Loss of smell is a strong signal that something is wrong and significant damage has been done. This simple smell test could provide a quick and inexpensive way to identify those who are already at high risk.”
The study published in the Journal of the American Geriatrics Society follows a related 2014 paper in which olfactory dysfunction was associated with an increased risk of death within five years. In that study, losing the sense of smell was a better predictor of death than a diagnosis of heart failure, cancer or lung disease.
For both studies the researchers used a well-validated tool called a “Sniffin’Stick” which looks like a felt-tip pen and has a distinct smell.
Participants smell each item and then identify that smell, one at a time, from a set of four choices. Those who got two or three right were considered “hyposmic,” defined as a reduced sense of smell, while those who managed one or none were labeled “anosmic,” having lost it completely.
The olfactory nerve is the only cranial nerve that is directly exposed to the environment. The cells that sense smell connect directly to the olfactory bulb at the base of the brain.
This may expose the central nervous system to environmental hazards such as pollution or pathogens. Olfactory problems are often an early sign of Parkinson’s or Alzheimer’s disease that gets worse as the disease progresses.
Professor Pinto said losing the ability to smell could have a significant impact on lifestyle and well-being. He explained: “Smell affects nutrition and mental health.
“People who cannot smell face everyday problems, such as knowing if food is spoiled, detecting smoke during a fire or assessing the need for a shower after exercise.
“Depression is closely related to not being able to smell because people don’t get that much pleasure in life.”
One of the early signs of dementia is the loss of smell and is only diagnosed after death. Professor of Psychology Martha McClintock at the University of Chicago said: “This ancient special sense may also be a key mechanism underlying human cognition.”
She also noted that the olfactory system contains stem cells that regenerate themselves. Professor McClintock added: “A reduction in the ability to smell may reflect a reduction in the brain’s ability to rebuild key parts that deteriorate with age, leading to pathological changes in many different dementias.”
Last month a Canadian study of 300 people at high risk of developing Alzheimer’s found that those who struggled to distinguish between the smells of bubblegum, petrol and lemon were more likely to have dementia-related proteins in their cerebrospinal fluid .
Around 850,000 people in the UK have dementia, a figure expected to rise to one million by 2025 and two million by 2050, due to the aging population.
