Loss of smell may be an early sign of Parkinson's and Alzheimer's

Smell is strongly associated with memory and emotion, and in fact the limbic system, including the amygdala and hippocampus, is responsible not only for memory and emotion, but also for olfactory processing. It has been pointed out that this deterioration and loss of smell may appear as an early symptom of neurodegenerative diseases such as Parkinson's disease and Alzheimer's disease .

Why Loss of Smell Can Be an Early Sign of Brain Diseases Like Alzheimer's.
https://nautil.us/loss-of-smell-may-be-an-early-sign-of-brain-diseases-354483/

Humans can obtain the sense of smell by detecting molecules that cause odors with the olfactory bulb in the nose and processing them in the limbic system. Although the mechanism of olfactory impairment has been roughly elucidated, the fundamental part is not clearly understood.

Human short-term memory seems to peak at the age of 25, but the sense of smell peaks around the age of 40 and then gradually begins to decline. In addition, a 2019 study showed that there is a gender difference in the sense of smell, and it seems that women have more olfactory cells, and men experience a greater decline in olfactory sense with age.

In a paper published in 2014, a four-year longitudinal study was conducted on 1162 healthy elderly people. The study reported that those with the lowest baseline olfactory scores had a 45% mortality rate over four years, compared with 18% for those with the highest scores. In addition, it seems that 70% of people who live in a state where they have lost their sense of smell do not realize that they have lost their sense of smell until they undergo an examination.

Olfactory impairment is also known as an early sign of various other diseases and is considered a marker of disease progression and cognitive impairment. There is also increasing evidence that it is actually an early sign of neurodegenerative diseases such as Huntington's disease , multiple sclerosis , and mild cognitive impairment .

In addition, a study published in 2022 showed that olfactory impairment develops as a symptom of the new coronavirus infection (COVID-19). The research team that published this paper argues that neuronal degeneration caused by the aggregation of defective proteins in COVID-19 and local inflammatory processes is the cause of olfactory impairment.

In addition, the research team said that the medulla oblongata, where the olfactory bulb and olfactory nerve are located, is the site where early onset is seen in Parkinson's disease, and this is the place where inflammation is seen even in infection with COVID-19. Therefore, the research team points out that both Parkinson's disease and COVID-19 may cause olfactory impairment as an early symptom due to neurodegeneration due to protein aggregation.

A study published in May 2023 also pointed out that olfactory disorders appear as an early symptom of Parkinson's disease.

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The sense of smell has not yet been clearly elucidated, and the principle of how olfactory disorders occur has not been identified. However, many studies have shown that olfactory disorders are an early symptom of various neurodegenerative diseases, so there is a good chance that olfactory disorders will trigger early detection. Christian Barbato, a researcher at the Institute of Biochemistry and Cell Biology at the University of Rome Sapienza, and his colleagues said, 'Highlighting the importance of the biological underpinnings of olfaction and molecular pathways is important for neuroprotection and therapy. It could be the basis for improving our strategy.”