Longevity

Longevity Briefs: Could Picking Your Nose Really Give You Dementia?

Posted on 15 November 2022

Longevity briefs provides a short summary of novel research in biology, medicine, or biotechnology that caught the attention of our researchers in Oxford, due to its potential to improve our health, wellbeing, and longevity.

Why is this research important: Do you pick your nose? Sorry if that’s a probing question. Research suggests that nose-picking, or rhinotillexis if you want to get fancy, is common among adults. Random surveys have estimated that up to 90% of adults are nose-pickers. Yet picking your nose could be far worse than just a gross habit. That’s because the olfactory nerve, which is responsible for carrying sensory information from the nose to the brain, can act as a kind of ‘back door’ allowing certain pathogens to bypass some of the protective mechanisms that protect the central nervous system from infection. SARS-CoV-2 is one example of a virus that might use this backdoor, potentially resulting in short or long-term loss of one’s sense of smell.

The existence of this pathway has led some scientists to wonder whether nose-picking might increase the risk neurodegenerative diseases. Damage to the lining of the nostrils could help pathogens to enter the brain via the olfactory nerve, resulting in increased inflammation and deposition of amyloid plaques, both of which are thought to be involved in dementia.

What did the researchers do: In this study, researchers wanted to investigate the effects of damage to the lining of the nostrils on the ability of a specific pathogen, called Chlamydia pneumoniae, to enter and damage the brains of mice. C. pneumoniae is a bacteria that can infect humans, and has been found in the brains of deceased late-onset dementia patients at around 8 times the frequency of control patients.

Researchers inoculated mice with C. pneumoniae via the nostrils, or gave them a sham inoculation. Some mice were treated with a medication called methimazole, which injures the lining of the nostrils. These mice were then euthanised at various stages up to 28 days later, and their brains were studied.

Key takeaway(s) from this research: C. pneumoniae was able to infect the cerebral cortex within three days of inoculation, but the amount of C. pneumoniae infecting the olfactory nerve and olfactory bulbs (located in the brain) were significantly higher in mice treated with methimazole after 7 days. Amyloid beta deposits, which are a key feature of Alzheimer’s disease, were found to be more concentrated around regions infected with C. pneumoniae. C. pneumoniae was also able to infect glial cells, which are the immune cells of the brain and are involved in preventing the build-up of amyloid plaques.

Graphs showing the infectious load in various locations 3 days (left) and 7 days (right) after infection in injured and uninjured mice. The bracket lines indicate values for which there was a significant difference.
Chlamydia pneumoniae can infect the central nervous system via the olfactory and trigeminal nerves and contributes to Alzheimer’s disease risk

So, does this mean that picking your nose makes you more at risk of neurodegenerative disease? We’d need to see human evidence to be sure, evidence that we currently lack. The structures of the mouse nose, olfactory nerve and brain are obviously not the same as their human counterparts, though there are parallels. It’s worthy of note that the mice used in this study weren’t genetically predisposed to develop amyloid plaques, which makes the findings concerning amyloid a little more relevant for human disease. Regardless, there’s a good argument to be made that nose-picking is a bad idea as it can damage the inner lining of the nostrils, which is likely to increase your risk of infection from various pathogens.


References

Chlamydia pneumoniae can infect the central nervous system via the olfactory and trigeminal nerves and contributes to Alzheimer’s disease risk: https://doi.org/10.1038/s41598-022-06749-9

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