Prevent memory loss with smell training? Olfactory enrichment proven effective in new research.
Study: Inflammation and loss of smell are associated with at least 139 medical conditions. Image credits: fizkes/Shutterstock.com
In a recent review article published in Frontiers in molecular scienceresearchers discussed the links between genetic, physical and neurological disorders and smell loss and inflammation.
They concluded that inflammation, the environment and neuroanatomy may link the loss of smell to several conditions and that stimulating the sense of smell may be useful in treating and preventing these health problems by reducing inflammation in the brain and body.
Health conditions and loss of smell
Olfactory disorders are linked to 139 medical conditions, including genetic or hereditary, physical and neurological disorders. Extensive research supports links to conditions such as rhinitis, depression, Parkinson’s disease, Alzheimer’s and coronavirus disease-2019 (COVID-19).
In many cases, loss of smell can occur before symptoms of the condition are experienced. This indicates that loss of smell could predict future cognitive decline and even mortality.
Olfactory senses are correlated with cognitive abilities such as decision-making, verbal fluency and memory. They are also a strong indicator of mortality and perform better as a predictor of cardiovascular disease.
There are differences between men and women, with olfactory thresholds in men highly correlated with executive function and language, but in women, olfactory discrimination is linked to visuospatial skills.
Causal mechanisms and underlying processes
The olfactory system can be affected by conditions that affect both the brain and the body. Neurological and somatic disorders can damage the olfactory system, while olfactory disorders can increase the risk of developing certain diseases. Olfactory disorders are often related to inflammation, which occurs in conditions such as hereditary and neurological disorders.
Inflammation can damage the olfactory system through inhaled substances (such as odors or pollution) or blood.
Conditions such as Parkinson’s disease show sniffing problems linked to airway inflammation, while loss of sense of smell in people with COVID-19 is also thought to be due to inflammation. However, some conditions, such as Kallmann syndrome, cause loss of smell without inflammation.
COVID-19 patients receive variable benefits from treatments, and nasal steroids effectively reduce inflammation in young adults. Olfactory training demonstrates age-dependent efficacy, especially in younger individuals with olfactory disorders. Animal studies show that certain scents (ginger, lavender and eucalyptus) have anti-inflammatory effects, indicating a possible therapeutic role.
Diet can also be a risk factor, with diets high in healthy fats linked to an increased risk of cognitive and smell loss. In mice, omega-3 supplementation prevented memory and smell loss.
Loss of smell is associated with memory loss, especially in dementia, due to direct brain pathways between smell and memory centers.
Brain areas involved in memory (the amygdala and hippocampus) deteriorate with loss of smell. Factors such as infections, stress, pollution and smoking can affect both the sense of smell and memory.
Longitudinal studies show that COVID-19-related smell loss predicts damage in memory-related brain regions, and that COVID-19 is associated with cognitive decline and an increased risk of Alzheimer’s disease.
Benefits of olfactory enrichment
Olfactory enrichment, or the process of stimulating the sense of smell, improves cognitive symptoms. Exposure to essential oils can improve brain health by balancing neurotransmitters, reducing oxidative stress and inflammation, and boosting cognition, memory, and neuroprotection.
There are also benefits for memory in older adults, as olfactory stimulation improves memory in healthy adults, especially older adults, through daily exposure to essential oils for months. Minimal nighttime olfactory enrichment (2 hours/night for 6 months) significantly improved memory scores in older adults.
In dementia patients, studies have shown that frequent exposure to scents helps improve memory, depression symptoms, attention and language skills. A rich olfactory environment, combined with education and social activities, can promote cognitive reserve and potentially protect against symptoms of dementia, even when the disease itself is present.
Researchers hypothesize that these benefits may be due to three mechanisms.
First, olfactory dysfunction and cognitive decline are linked to inflammation, and pleasant smells can reduce inflammation, potentially helping with memory and cognitive symptoms in neurological disorders.
Second, daily exposure to olfaction can expand the olfactory processing areas of the brain, potentially boosting memory and cognitive function. The third could be due to electrical stimulation, as stimulating the olfactory bulb has shown promise in animal models in reducing beta-amyloid plaque (associated with Alzheimer’s disease) and improving working memory.
Conclusions
Olfactory disorders are linked to at least 139 medical conditions. Often, loss of smell occurs before the symptoms of the medical condition, suggesting that it may increase vulnerability to these conditions and predict memory loss and an increased risk of mortality.
Inflammation may play a key role in linking olfactory disorders to memory problems and other medical symptoms, but environmental and neuroanatomical influences also contribute, potentially creating a bidirectional relationship.
Olfactory enrichment may improve memory in both healthy and dementia-affected adults, possibly due to its anti-inflammatory effects. Pleasant scents can help reduce inflammation and possibly alleviate symptoms of several medical conditions.