Viruses are pesky and inconvenient. They might cause us to sneeze and sniffle for a few days or cause more serious symptoms, as in the case of COVID-19 or influenza. But could they also play a role in more serious health problems, like Alzheimer’s disease?
A troubling link between viral infections and brain health has come to light, based on a new study published in the journal Neuron. Led by Mike Nalls at the National Institutes of Health, the 15-year study uncovers how common illnesses like the flu, stomach bugs, or even the common cold could silently increase one’s risk for neurodegenerative diseases like Alzheimer’s and Parkinson’s later in life.
The Scope of the Study
Examining medical records from over 450,000 people living in Finland and the United Kingdom, Nalls, and his research team set out to uncover if there could be a link between past viral infections and one’s likelihood of developing neurodegenerative diseases down the road. Specifically, they wondered whether contracting any of twelve common viral infections earlier in life might be linked to later developing one of six major neurodegenerative brain diseases. These include the infamous memory-destroying Alzheimer’s, the movement-impairing Parkinson’s, and the nerve-degenerating multiple sclerosis.
By closely analyzing the extensive records tracking major illness episodes over the decades in these individuals, the scientists wanted to know whether coming down with a common cold, flu, or other virus at a young age correlates with or even contributes to the odds of suffering these devastating neurological conditions further down the road.
The researchers were eager to identify any early risk factors, subtle though they may be, that might one day help us better predict, prevent, or treat these presently incurable conditions. Could they subtly contribute to diseases like Alzheimer’s and Parkinson’s in some people, either initiating the disease process or accelerating its emergence? By uncovering whether viral exposures are linked to neurodegenerative disease onset, Nalls’ team hopes to open new possibilities for understanding brain health decline while also pointing to preventative approaches people could take to safeguard cognitive wellbeing over the long term.
What The Scientists Found about Viruses and Neurodegenerative Diseases
Among the viral illnesses analyzed, pneumonia triggered by flu virus emerged as a leading risk factor for multiple neurodegenerative diseases later in life. Study participants who had come down with flu-related pneumonia showed higher rates of developing Alzheimer’s, Parkinson’s and other neurodegenerative conditions down the road compared to those without pneumonia in their medical history. It’s as if severe viral respiratory infections are causing irreparable damage that alters disease trajectories much later on for some people.”
The research team also found that past viral infections directly affecting the brain – specifically encephalitis and meningitis – posed the highest future risk for Alzheimer’s disease out of the neurodegenerative conditions examined.
Viral infections like encephalitis and meningitis that make their way into brain tissue can leave behind inflammatory changes that increase the risk of degenerative brain changes later. Individuals with past viral infections like herpes, and gastroenteritis have markedly higher chances over the long term of developing the array of neurodegenerative diseases examined in the study, including Alzheimer’s, Parkinson’s, and multiple sclerosis.
The findings illuminate how even common viruses tend to leave behind physiological changes in some people that make the brain more vulnerable to degeneration as they age. The data underscores how viral exposures silently alter neurological disease trajectories in ways we are only beginning to understand. Now, scientists need to determine what’s driving these changes, so we can limit the damage and avoid viruses that trigger these changes.
Could Vaccination Make a Difference?
Could vaccinating against common viruses lower the risk of brain diseases like Alzheimer’s and Parkinson’s disease? There is some evidence that vaccination may help protect against certain neurodegenerative brain diseases like Alzheimer’s disease and Parkinson’s disease.
Several studies found associations between routine adult vaccinations like the flu shot and vaccines for shingles, tetanus, diphtheria, and pneumonia and a reduced risk of developing Alzheimer’s disease later in. The mechanisms behind this protective effect are still being investigated, but hypotheses include that vaccines may:
- Prevent infections that can cause inflammation in the brain.
- Enhance the immune system’s ability to clear toxic proteins like amyloid beta that build up in Alzheimer’s.
- Modulate the immune response to prevent over-activation against Alzheimer’s proteins.
This is an area that still needs more research.
Is the Severity of a Viral Infection a Factor?
Several studies have uncovered links between viral infections, particularly those that attack the nervous system, and a heightened risk for neurodegenerative diseases down the road, like Alzheimer’s, Parkinson’s, ALS, and multiple sclerosis. The most robust association was between viral encephalitis and Alzheimer’s disease, with a whopping thirty times higher risk compared to the general population.
Other culprits include influenza strains that make people sick enough to be hospitalized. Experts believe the inflammation and immune assault triggered by these viruses may contribute to later nerve cell damage. Fortunately, we have vaccines for some of these viruses. Getting vaccinated could be one way to potentially curb neurodegenerative disease risk.
Additional viruses like herpes simplex and Epstein-Barr have been tied to Alzheimer’s and multiple sclerosis, respectively. The virus may directly damage nerve cells or spark damaging neuroinflammation. The danger seems greatest around the time of infection but stays elevated for years for some viruses, indicating both immediate and chronic effects are at play.
In a nutshell, there is evidence that coming down with certain viral illnesses, especially ones that infiltrate the nervous system, can stoke neuroinflammation and neurodegeneration later in life. Vaccination may offer one route to mitigating those risks, based on the associations discovered so far. But more study is still required to fully understand the precise mechanisms linking viruses and neurodegenerative disease.
Conclusion
The connection between viral infections and brain health is complex, and degenerative brain diseases are triggered by multiple factors, including genetics, lifestyle, and traumatic events, like head injuries. But these studies show that viruses could also trigger cascading effects in the brain that contribute to brain degeneration and health issues like Parkinson’s and Alzheimer’s
So, prioritize brain and immune health! While you can’t avoid all viral infections, lifestyle strategies like managing stress, getting sufficient sleep, following a nutritious diet, exercising, and staying socially and mentally active could help your immune system better fight off those annoying viruses. Plus, it could equip your brain to better handle viral-induced changes, thereby reducing the likelihood of developing neurodegenerative conditions. Taking these steps is beneficial for your health too.
References:
- Levine KS, Leonard HL, Blauwendraat C, Iwaki H, Johnson N, Bandres-Ciga S, Ferrucci L, Faghri F, Singleton AB, Nalls MA. Virus exposure and neurodegenerative disease risk across national biobanks. Neuron. 2023 Apr 5;111(7):1086-1093.e2. Epub 2023 Jan 19 PubMed.
- Nothing to Sneeze At: Viruses Raise Risk of Neurodegenerative Disease | ALZFORUM. Alzforum.org. Published February 2, 2023. Accessed February 24, 2024. https://www.alzforum.org/news/research-news/nothing-sneeze-viruses-raise-risk-neurodegenerative-disease?utm_source=pocket_saves
- ”NIH-funded study finds new evidence that viruses may play a role in ….” 21 Jun. 2018, https://www.nih.gov/news-events/news-releases/nih-funded-study-finds-new-evidence-viruses-may-play-role-alzheimers-disease.
- “Harder Evidence Builds That Viruses Play a Role in Alzheimer’s.” 21 Jun. 2018, https://www.scientificamerican.com/article/harder-evidence-builds-that-viruses-play-a-role-in-alzheimers/.
- Verreault R, Laurin D, Lindsay J, De Serres G. Past exposure to vaccines and subsequent risk of Alzheimer’s disease. CMAJ. 2001 Nov 27;165(11):1495-8. PMID: 11762573; PMCID: PMC81665.
- “Viral role in Alzheimer’s Disease discovered | University of Oxford.” 02 Aug. 2022, https://www.ox.ac.uk/news/2022-08-02-viral-role-alzheimers-disease-discovered.
- https://www.facebook.com/NIHAging. Could a viral illness increase the chances of developing Alzheimer’s or other neurodegenerative diseases? National Institute on Aging. Published January 19, 2023. Accessed February 24, 2024. https://www.nia.nih.gov/news/could-viral-illness-increase-chances-developing-alzheimers-or-other-neurodegenerative-disease
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