Emerging research from Stanford University and other leading institutions suggests that the shingles virus, which affects millions of Americans annually, could significantly increase the risk of developing Alzheimer's disease. This potential connection between viral infections and dementia is offering new hope in solving the long-standing mystery of Alzheimer's, a condition affecting millions worldwide.
Shingles, caused by the varicella-zoster virus-the same virus that leads to chickenpox-may be more than just a painful rash. According to a study led by epidemiologist Dr. Pascal Geldsetzer from Stanford University, people who received a shingles vaccine were 20% less likely to develop Alzheimer's compared to those who did not. "We're looking at a causal effect," Dr. Geldsetzer told STAT. "And it's specific to dementia. There is something clearly going on here."
The virus, which remains dormant in the nervous system after an individual recovers from chickenpox, can reactivate later in life, causing shingles. Factors such as aging or illness, which weaken the immune system, can trigger this reactivation. Researchers believe that this reactivation may play a role in the onset of dementia, though the exact biological mechanisms remain unclear.
Dr. Geldsetzer's research, yet to be peer-reviewed but made publicly available by the National Institute of Health, analyzed health records of 300,000 people born in Wales between 1925 and 1942. The study took advantage of vaccination guidelines in Wales, which had an age cutoff that excluded individuals over 80. This allowed for a direct comparison between those who were vaccinated against shingles and those who were not. The results were striking-vaccination appeared to significantly reduce the risk of dementia in the seven years following inoculation.
To validate these findings, the researchers replicated the study in both the United Kingdom and Australia, observing similar trends. Meanwhile, a separate study conducted by Oxford University, published in the journal Nature, examined the health records of 200,000 Americans. This research found that individuals who received a newer shingles vaccine, Shingrix, were 17% less likely to develop dementia in the six years following vaccination compared to those who received older vaccines.
Paul Harrison, the lead author of the Oxford study, highlighted the broader implications of vaccination, saying, "I've always been a vaccine believer, but the COVID vaccine reinforced to me that there may be long-term benefits to vaccination beyond simply stopping short-term effects." His comments reflect growing optimism that vaccines could play a crucial role in reducing the risk of neurodegenerative diseases.
The link between shingles and dementia is still a nascent area of research, but it is generating significant interest. Scientists speculate that while the virus lies dormant in the nervous system, the immune system must work constantly to keep it in check. As people age, their immune system weakens, potentially allowing the virus to impact other parts of the body, including the brain. Researchers from the University of Alabama have suggested that the virus might affect blood vessels, disrupting blood flow to the brain, which over time could lead to cognitive decline and increase the risk of dementia.
The concept that infections could contribute to neurodegenerative diseases is gaining traction. Recent studies, including one published in Nature Aging, have shown that other severe infections, such as the flu and respiratory tract infections, are also linked to an increased risk of dementia and brain atrophy. The study, led by Keenan Walker from the National Institute on Aging, found that individuals with a history of severe infections experienced accelerated loss of brain volume, particularly in areas associated with memory.
Kristen Funk, an assistant professor at the University of North Carolina at Charlotte, emphasized the importance of vaccines in this context. "Vaccines are going to be the most protection against both the acute infection as well as these post-infectious effects," she said. The idea that infections can influence brain health, once considered fringe, has gained momentum, especially after the cognitive impacts observed following COVID-19.
Despite the promising findings, scientists caution that much work remains to be done to establish a definitive causal link between shingles and Alzheimer's. Charlotte Warren-Gash, a professor of epidemiology at the London School of Hygiene and Tropical Medicine, noted that while the studies provide important insights, they primarily show correlation rather than causation. More research is needed to understand the biological pathways, including the role of immune-related proteins and the well-known Alzheimer's biomarkers like amyloid plaques and tau tangles.
Dr. Maria Nagel, a neurovirologist from the University of Colorado, expressed hope that the increasing interest in the role of viruses in Alzheimer's could lead to significant breakthroughs. "I really do believe that in the next 10 years or so we're going to see huge strides in finding new mechanisms and finding new ways to try to slow things down," she said. This shift in focus could lead to innovative approaches for preventing or slowing the progression of Alzheimer's.
