Study finds loss of smell linked with inflammation in 140 conditions, could be early sign of disease

A loss of smell — once a telltale sign of COVID-19 — has been linked with inflammation in nearly 140 medical conditions, including those related to ageing and menopause, and therefore, could be an early sign of neurological and bodily diseases, according to a study.

Researchers said the results highlighted the role that our sense of smell plays in maintaining physical and mental health.

“The data are particularly interesting because we had previously found that olfactory (smell-related) enrichment can improve the memory of older adults by 226 per cent,” Michael Leon, a professor emeritus at the University of California-Irvine, US, and lead author of the study published in the journal Frontiers in Molecular Neuroscience, said.

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

The findings could have implications for addressing symptoms and possibly reducing onset of certain disease by treating one’s sense of smell, which can often precede ageing-related conditions such as Alzheimer’s and Parkinson’s diseases, the researchers proposed.

For the study, the researchers tracked 139 medical conditions related to both a loss of smell and heightened inflammation, thereby uncovering insights into a route shared between the two symptoms.

Given that linking a loss of smell with a wide range of disorders is complex, tracking down studies for several medical conditions was difficult, Leon said.

Majority of the studies the team looked at (9,000) pertained to long Covid’s loss of smell, while close to 2,000 looked at olfactory loss due to ageing-related memory loss. About 3,900 studies explored loss of smell in menopause and 3,500 pertained to loss of smell in depression.

“Olfactory loss accompanies at least 139 neurological, somatic, and congenital/hereditary conditions,” the authors wrote.

“Mechanisms that may underlie the connections between medical conditions and olfactory loss include inflammation as well as neuroanatomical and environmental factors, and all 139 of the medical conditions listed here are also associated with inflammation,” they wrote.

The findings about how rehabilitating one’s sense of smell can potentially address inflammation has laid groundwork for future studies aiming to explore the use of scent in treating a range of medical conditions, the researchers said.