A new study has found that the smell of menthol can improve cognitive abilities and stop some of the brain damage associated with Alzheimer’s disease. Researchers at the Center for Applied Medical Research (CIMA) in Spain discovered that when mice with Alzheimer’s inhaled menthol, there was a reduction in the inflammatory protein Interleukin-1-beta (IL-1β), which leads to harm when not controlled properly. The researchers showed that smelling menthol could improve the cognitive abilities of healthy young mice as well as preventing cognitive decline in the mice with Alzheimer’s. This study shows the potential for particular smells to be used as therapies for Alzheimer’s, pending further investigation.
The study discovered that the smell of menthol was an immunostimulatory odor in animal models, however, it was surprising to find that it had a positive impact on cognitive abilities in mice. Having previously observed that menthol inhalation boosted the immune response of mice, the researchers discovered that the same menthol could also improve the animals’ cognitive abilities in lab tests.
The course of menthol for a six-month-long period was sufficient to stop the cognitive abilities and memory capabilities of mice with Alzheimer’s from deteriorating. In addition, it appears that the menthol pushed the IL-1β protein back to safe levels in the brain. When researchers artificially reduced the number of T regulatory (Treg) cells – known to help keep the immune system in check – some of the same effects were observed, opening a possible route that future treatments could take.
It is already established that there are numerous links between smells and the immune and nervous systems. Researchers know that our olfactory system can strongly influence the brain and that certain smells may trigger certain responses in the brain, leading to chemical reactions that affect memory, emotion, and more. Diseases linked to the central nervous system often come with a loss of smell, including Alzheimer’s, Parkinson’s, and schizophrenia.
The research adds some promising data, but plenty more is needed in humans as well as mice. The study is an important step towards understanding the connection between the immune system, the central nervous system, and smell. 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.
In human volunteers, scientists have previously shown how inhaling certain odors can lead to changes in brain activity. In one study, smelling rosemary essential oil improved cognitive performance and mood in healthy adults, while in another study, inhaling lavender oil reduced anxiety.
It’s thought that the effect inhaling smells has on the brain could be related to the ways in which different scents can interact with neurotransmitters. These are the chemicals in the brain which allow nerve cells to communicate with each other, and are important for memory and learning, as well as regulating mood.
While the new study adds to our understanding of the complex relationship between smell, the immune system, and the central nervous system in Alzheimer’s disease, its findings cannot yet be applied to humans. Nevertheless, it provides hope that a better understanding of how odor affects the immune and nervous systems could shed light on new ways to prevent and treat Alzheimer’s and other diseases related to the central nervous system.
