A new study suggests a single episode of shingles can predict the onset of dementia years in advance.
Shingles is an infection that causes a painful red rash. It can appear as blotches on your skin, on one side of your body only.
It's caused by the varicella zoster virus (VZV), the same virus that causes chickenpox. After a person has chickenpox, the virus stays in their body for the rest of their life. Most of the time, our immune system keeps the virus at bay. Years and even decades later, the virus may reactivate as shingles.
Previous studies of shingles and dementia have been conflicting. Some research indicates that shingles increases the risk of dementia, while others indicate there's no association or a negative association.
There's a growing body of evidence that herpes viruses, including VZV, can influence cognitive decline, the earliest sign of Alzheimer's disease.
The blotches become itchy blisters that ooze fluid
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Researchers from Brigham and Women’s Hospital investigated whether the same can be said for shingles.
Corresponding author Sharon Curhan and her team used data from three large, well-characterised studies of men and women over long periods:
The study, published in Alzheimer's Research & Therapy, included 149,327 participants who completed health status surveys every two years, including questions about shingles episodes and cognitive decline. They compared those who had shingles with those who didn't.
The researchers found that a history of shingles was significantly and independently associated with a higher risk—approximately 20 per cent higher—of subjective cognitive decline in both women and men.
That risk was higher among men who were carriers of the gene APOE4, which is linked to cognitive impairment and dementia. That same association wasn't present in the women.
Researchers don't know the mechanisms that link the virus to cognitive health, but there are several possible ways it may contribute to cognitive decline.
There is growing evidence linking VZV to vascular disease, called VZV vasculopathy, in which the virus causes damage to blood vessels in the brain or body. Curhan’s group previously found that shingles was associated with higher long-term risk of stroke or heart disease.
Other mechanisms that may explain how the virus may lead to cognitive decline include causing inflammation in the brain, directly damaging the nerve and brain cells, and the activation of other herpesviruses.
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Several mutations in components of the spike protein raise concerns over vaccine efficacy Getty Images What the study does make clear is that getting vaccinated against shingles is critical.
In recent studies, the shingles vaccine was associated with a reduced risk of dementia.
"Our findings show long-term implications of shingles and highlight the importance of public health efforts to prevent and promote uptake of the shingles vaccine," Curhan said.
The limitations of this research include that it was an observational study, information was based on self-reporting, and included a mostly white, highly educated population. In future studies, the researchers hope to learn more about preventing shingles and its complications.
“We’re evaluating to see if we can identify risk factors that could be modified to help reduce people’s risk of developing shingles,” Curhan said. “We also want to study whether the shingles vaccine can help reduce the risk of adverse health outcomes from shingles, such as cardiovascular disease and cognitive decline.”
