The olfactory system, which helps us process smells, has been linked with Alzheimer’s in past research, with one study finding that olfactory inflammation from viruses may hasten the onset of the disease. What about sniffing certain substances as a possible treatment? A new study investigated this, with a specific substance.
Research recently published in Frontiers in Immunology looked at the impact of inhaling menthol in mice with Alzheimer’s disease. The team found that repeated short exposures to menthol was linked with immune system modification and improved cognitive ability.
Dr. Noelia Casares, the study’s first author and researcher at the Immunology and Immunotherapy Program at Cima University of Navarra, says, “This study is an important step toward understanding the connection between the immune system, the central nervous system and smell, as the results suggest that odors and immune modulators may play an important role in the prevention and treatment of Alzheimer’s and other diseases related to the central nervous system.”
Through their research, the team found that smelling menthol reduced the level of interleukin-1-beta, a protein that moderates the inflammatory response. When they then hindered the protein with a medication used to treat some autoimmune diseases, there was also an improvement in the mice’s cognitive ability.
Dr. Juan José Lasarte, principal author and director of the Immunology and Immunotherapy Program at Cima, says, “We have focused on the olfactory system’s role in the immune and central nervous systems, and we have confirmed that menthol is an immunostimulatory odor in animal models. But, surprisingly, we observed that short exposures to this substance for six months prevented cognitive decline in the mice with Alzheimer’s and, what is most interesting, also improved the cognitive ability of healthy young mice.”
The team also observed that blocking the activity of T regulatory cells, which have immunosuppressive capabilities, had the same effect. Both the menthol exposure and this cell blocking decreased the level of interleukin-1-beta.
The research was part of the INNOLFACT project, which is investigating how the olfactory system functions as we age and aims to develop new immunomodulatory treatments to slow the development of neurodegenerative diseases.
While this research showed the brain impacts of smelling certain substances, other research has shown that not being able to smell may be a sign of looming brain issues, as rapid olfactory decline during aging has been linked with dementia.