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

The symptoms often caused by the common cold have been linked to 139 different diseases.

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

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Loss of sense of smell is a common side effect of illnesses such as colds and allergies.

It also served as a precursor to Covid-19 in the early days of the pandemic, with many remaining unable to smell for weeks after catching the virus.

But scientists from the Charlie Dunlop School of Biological Sciences at the University of California, Irvine, in California, US, say the seemingly harmless symptoms are nothing to sniff at, as persistent loss of smell can be an early sign of many different diseases.

“There is reason to believe that the relationship between anosmia and medical conditions may be more than just a coincidence,” they wrote in the journal Frontiers in Molecular Neuroscience.

“First, there are many cases in which both are present, with at least 139 medical conditions showing an association with olfaction.

“Second, anosmia precedes the expression of a medical condition, raising the possibility that anosmia predisposes the brain or body to the expression of symptoms of these medical conditions.

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

By analyzing a number of different studies, scientists were able to link the loss of the sense of smell to hundreds of different diseases.

They also found that it may be an early symptom of some underlying conditions.

“Anosmia appears before any other symptoms of Parkinson's disease,” the researchers wrote. “Similarly, one of the early symptoms of Alzheimer's disease is anosmia, as the first part of the brain to deteriorate in this disease is the olfactory pathway.”

A poor sense of smell has been linked to schizophrenia, with symptoms appearing in young people who develop the mental health condition.

“Anosmia also precedes depression, major cardiac events and multiple sclerosis,” the scientists continued, noting that the sign could appear before other recognized symptoms of these conditions.

“Studies for many medical conditions have been difficult to track down,” said Emeritus Professor Michael Lyon, who led the study.

But he said the findings on anosmia may also pave the way for treating certain diseases, through methods such as “therapeutic olfactory stimulation.”

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

“The data is particularly interesting because we previously found that olfactory enrichment can improve older people's memory by 226 percent,” Professor Lyon added.

“We now know that pleasant scents can reduce inflammation, suggesting a mechanism by which these scents may improve brain health.”

The study authors said their research has laid the foundation for future Studies aim to explore the therapeutic use of aroma to treat a wide range of medical conditions.

Professor Lyons said: “It will be interesting to see if we can improve the symptoms of other medical conditions by enriching the sense of smell.”

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

They said it could serve as a non-surgical way to improve health outcomes for people with various conditions.

This comes after a study published by the University of Chicago found that a rapid decline in the sense of smell could be an early indicator of dementia.