Olfactory enrichment offers promise as a therapeutic tool

By Stephanie Feuer

A groundbreaking study from the University of California, Irvine has revealed a startling connection between loss of smell and more than 130 different medical conditions, suggesting that our sense of smell plays a far more crucial role in our health than previously understood. The extensive range of conditions suggests a deeper, more fundamental connection between our sense of smell and overall health.

The study, which appears in Frontiers in Molecular Neuroscience,  categorizes these conditions into three main groups: neurological conditions, somatic (body-wide) disorders, and congenital/hereditary disorders. 

Smell Loss as an Early Warning for Neurological Conditions

The neurological conditions linked to smell loss paint a particularly compelling picture. Beyond the well-known connections to Alzheimer's and Parkinson's disease, researchers found links to multiple sclerosis, schizophrenia, epilepsy, and various forms of dementia. The data shows that olfactory dysfunction often appears before other symptoms, making it a potential early warning system for these conditions.

Smell Loss Linked to Conditions in Virtually Every Body System 

In the realm of somatic disorders, the connections are equally diverse and surprising. The study found links between smell loss and conditions affecting all our major body systems including:

- Cardiovascular: Heart disease and major cardiac events

- Respiratory: Various types of lung diseases

- Metabolic: Diabetes and thyroid disorders

- Autoimmune: Lupus and rheumatoid arthritis

- Psychiatric: Depression and anxiety disorders

Smell Loss a Symptom of Genetic Disorders

Even congenital and hereditary conditions, including Bardet-Biedl syndrome, Cystic fibrosis, Down Syndrome, Gaucher disease and others show connections to olfactory dysfunction, suggesting that smell loss might be an underappreciated symptom of genetic disorders.

Three Possible Reasons for the Connection Between Smell Loss and Medical Conditions

The study proposes three possible mechanisms behind these connections. First, there might be a common factor affecting both the olfactory system and various body systems. Second, certain medical conditions might produce substances that damage the smell system. Third, the olfactory system itself might generate compounds that increase vulnerability to disease.

 

Inflammation and Olfactory Enrichment as a Therapeutic Tool

The inflammation connection is particularly intriguing. All 139 medical conditions identified in the study share increased inflammation as a common factor. The study suggests that olfactory enrichment may be a way to attenuate symptoms or even stave off the onset of some of these conditions by addressing inflammation. 

 “We now know that pleasant scents can decrease inflammation, potentially pointing to the mechanism by which such scents can improve brain health,” said UC Irvine’s Professor Emeritus Michael Leon, the lead researcher. “The data are particularly interesting because we had previously found that olfactory enrichment can improve the memory of older adults by 226%.”

The concept is particularly promising because the olfactory system has direct connections to memory centers in the brain—the only sensory system with such direct neural pathways. This might explain why smell loss often precedes memory-related conditions.

Smell and Cognitive Reserve

The study also sheds light on the concept of cognitive reserve—the brain's resilience to neurological damage. Some individuals can have the physical markers of Alzheimer's disease without showing memory loss symptoms, thanks to this reserve. The research suggests that the olfactory system might play a crucial role in building and maintaining this cognitive resilience, particularly for memory-related conditions.

 

The researchers cite multiple studies which indicate that olfactory ability can predict all-cause mortality up to 17 years in advance—with higher accuracy than predictions based on heart disease. In older adults, doctors can even predict the probability of developing mild cognitive impairment or even Alzheimer's disease based on their sense of smell.

This study opens several promising avenues for future investigation. These include examining the relationships between smell, inflammation, and specific medical conditions, as well as conducting longitudinal studies of individuals with olfactory dysfunction. The researchers are furthering their work on the promise of olfactory enrichment as a potential key to mitigating the symptoms or onset of a range of diseases.