A minty cure? Smelling menthol reduces symptoms of Alzheimer’s disease

PAMPLONA, Spain — Could the right odor hold the secret to curing Alzheimer’s disease? Researchers in Spain have discovered that inhaling menthol — an organic compound created using various types of mints — regulates the immune system and improves the cognitive function of animals suffering from the neurodegenerative disease. Scientists at Cima Universidad de Navarra believe this discovery opens the door to creating new odor-based therapies that can reverse the effects of Alzheimer’s — the most common form of dementia worldwide.

What is menthol?

Many people are probably familiar with menthol being an ingredient in smoking and vaping products, but it actually has several other applications. Menthol is an organic compound made synthetically or obtained from the oils of corn mint, peppermint, or other mints. It is a waxy, crystalline substance, clear or white in color, which is solid at room temperature and melts in warmer air.

Menthol has a minty smell and produces a cooling sensation when people apply it to their skin or ingest it. Some of the products which use menthol include:

• Medicine: It’s an ingredient in non-prescription products for short-term relief of minor sore throats and minor mouth or throat irritation. It is also a part of many cough and cold products, medications for digestive problems, and in some topical pain relievers.
• Cosmetics and personal care products: Manufacturers use menthol in lip balms and glosses, hair care products, and skin care products. The cooling sensation of menthol is especially popular in products used after sun exposure, in foot creams, and in shaving creams.
• Food and drinks: It is a flavoring in several foods and beverages.
• Tobacco products: Menthol is used in some cigarettes and tobacco products, which has been a controversial use due to public health concerns.

Despite stimulating the cold-sensitive thermoreceptors in the skin, menthol doesn’t actually lower body temperature.

So, how does it protect the brain?

Researchers found that smelling this substance even briefly can prevent cognitive deterioration, which is a typical side-effect of Alzheimer’s onset. A detailed study revealed that smelling the aroma lowered levels of interleukin-1-beta (IL-1β), a critical protein that mediates the body’s inflammatory response. When scientists further inhibited this protein with an autoimmune disease drug, mice with Alzheimer’s saw their cognitive abilities improve.

Study authors note that our brains depend on a fragile balance of interactions between nerve cells, immune cells, and neural stem cells in order to function correctly. Studies continue to show that odors can play a key role in regulating these healthy interactions. Moreover, a loss of smell is often one of the first symptoms Alzheimer’s patients experience.

“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,” says Dr. Juan José Lasarte, the director of the Program of Immunology and Immunotherapy at Cima and principal author of the investigation, in a media release.

The team adds that blocking the activity of T regulatory cells (a type of immune cell) also helped to improve the cognitive performance of mice with Alzheimer’s. It also produced a clear benefit for younger, healthy mice as well.

“Both menthol exposure and Treg cell blockade caused a decrease in IL-1β, a protein that could be behind the cognitive decline observed in these models,” notes co-author Dr. Ana García-Osta.

“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,” first author Dr. Noelia Casares concludes.

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The findings are published in the journal Frontiers in Immunology.