Common cold symptom ‘could be an early warning sign of 139 diseases’ – see the full list

A SYMPTOM often triggered by the common cold has been linked to a staggering 139 different diseases.

A study found it could be an early sign of everything from Alzheimer’s to Parkinson’s.

Losing your sense of smell is a common side effect of ailments such as colds and allergies.

It also served as an indicator of Covid-19 in the early days of the pandemic, with many left unable to smell for weeks after picking up the virus.

But scientists from UC Irvine Charlie Dunlop School of Biological Sciences in California, US, say the seemingly harmless symptom is not something to be sniffed at – as persistent smell loss could be an early sign of several different diseases.

“There is reason to believe that the relationship between olfactory loss and medical conditions may be more than coincidental,” they wrote in the journal Frontiers in Molecular Neuroscience.

“First, there are many instances where both are present, with at least 139 medical conditions showing associations with olfactory dysfunction.

“Second, olfactory loss precedes the expression of the medical condition, raising the possibility that olfactory loss makes the brain or body vulnerable to expressing the symptoms of these medical conditions.

“Third, olfactory loss prospectively predicts both memory loss and all-cause mortality.”

Analysing a number of different studies, scientists were able to link smell loss to hundreds of different diseases.

They also found that it may be an early symptom of a few key conditions.

“Olfactory loss appears well before any other Parkinson’s symptoms and similarly, an early symptom of Alzheimer’s disease is the loss of olfaction, with the first part of the brain to deteriorate in that disease being the olfactory pathway,” the researchers wrote.

A poor sense of smell has been linked to schizophrenia, with the symptom seen in young people who go on to develop the mental health condition.

“Olfactory loss also precedes depression, major cardiac events and multiple sclerosis,” the scientists went on – indicating that the sign can appear before other recognised symptoms of the conditions.

Professor emeritus Michael Leon, who led the study, said: “It was difficult to track down the studies for so many medical conditions.”

But he said the findings around smell loss may also pave the way for treating certain diseases, through methods such as “therapeutic olfactory stimulation“.

Previous research by Prof Leon and his team found that “olfactory enrichment” – exposing people to new scents on a daily basis – could improve memory.

Prof Leon added: “The data are particularly interesting because we had previously found that olfactory enrichment can improve the memory of older adults by 226 per cent.

“We now know that pleasant scents can decrease inflammation, potentially pointing to the mechanism by which such scents can improve brain health.”

The study authors said their research has laid a foundation for future studies aiming to explore the therapeutic use of scent to address a broad range of medical conditions.

“It will be interesting to see if we can ameliorate the symptoms of other medical conditions with olfactory enrichment,” Prof Leon said.

He and his team are now working on a device to deliver olfactory therapy.

They said it could work as a non-invasive way of improving health outcomes of people with various conditions.

It comes after a study, published by the University of Chicago, found a rapid decline in sense of smell can be an early indicator of dementia.