Inflammation and loss of sense of smell have been linked to 139 diseases

A research team from the University of California (USA) and the University of Oxford (UK) has identified a link between olfactory loss, inflammation and 139 different diseases, including neurological, somatic, congenital or hereditary pathologies.

The sense of smell plays an important role in human life, and its loss, or anosmia, is associated with Alzheimer's, Parkinson's and depression, acting as a precursor to pathologies, allowing their early detection. Anosmia was also considered a key symptom of coronavirus infection during the Covid-19 pandemic.

The results of the study, published in the journal Frontiers in Molecular Neuroscience, however, revealed that this is just the tip of the iceberg. It turned out that the loss or deterioration of the sense of smell may indicate the development of 139 different diseases characterized by increased levels of inflammation in the body. The latter can directly damage the olfactory system due to external factors such as infections or air pollution. In some cases, inflammation accompanies the ailment and participates in its development.  

After reviewing 139 medical conditions in which there is a loss of smell and increased levels of inflammation, the team of scientists found that damage to the olfactory system is directly linked to areas of the brain responsible for processing memory and emotion. Specifically, loss of the sense of smell is seen in dementia, which led the researchers to raise questions about exactly what role it plays in memory loss.

“The olfactory system is anatomically unique among all sensory organs in that it has a 'superhighway' that bypasses the thalamus and projects directly to brain regions involved in memory processing,” the authors of the research paper wrote. 

While disruption of certain parts of the brain may be linked to the loss of the sense of smell, the study authors did not rule out that causes of anosmia, such as air pollution, stress, smoking, taking medications and chronic sinusitis, contribute to damage in other areas of the brain. 

Having identified inflammation as a possible factor linking anosmia, disease and mortality (as well as neuroanatomical factors contributing to memory, cognitive function and olfactory decline), the researchers suggested that each individual's specific life experiences could activate such links. 

The results of the new study also demonstrated that stimulating the olfactory system with a variety of odors can lead to reduced levels of inflammation and improved olfactory abilities. For this reason, the team hypothesized that stimulating the olfactory system reduces inflammation levels in the body, but there is no direct evidence of this effect in the paper.

Nevertheless, the discovery lays the groundwork for future research to explore olfactory therapy (a wide range of techniques aimed at restoring and improving olfactory and cognitive abilities, including aromatherapy and psychological counseling) as a way to treat a wide range of conditions associated with anosmia and inflammation in the body. 

The results also emphasize the important role of olfaction in assessing overall physical and mental health and may lead to the development of new methods for diagnosis and prevention of various medical conditions.