Scientists have speculated that shingles could increase the risk of dementia. However, new research has found that shingles is not associated with an increased risk of dementia.
Shingles is a viral infection caused by the reactivation of the chickenpox virus that results in a painful blistering rash along one side of the body or face from nerve inflammation. Because of such inflammation, there has been scientific speculation that shingles may increase a person’s risk of dementia. However, shingles is not associated with an increased risk of dementia according to the results of new research. The study was recently published in Neurology, the medical journal of the American Academy of Neurology.
“As a person’s age increases, so does their risk of dementia, and it’s important to determine which factors may contribute to this risk,” said study author Sigrun Alba Johannesdottir Schmidt, MD, PhD, of Aarhus University Hospital in Denmark. “Shingles most often affects people over age 50. The good news is that our study found it does not seem to increase a person’s risk for dementia.”
Scientists reviewed Danish medical registries for the research. They identified 247,305 people who had visited a hospital for shingles or were prescribed antiviral medication for shingles, and 1,235,890 people matched for age and sex who did not have the disease over a 20 year period. The average age was 64.
Researchers then examined which participants developed dementia up to 21 years after their shingles diagnosis. 9.7% of the people who had shingles eventually developed dementia. 10.3% of people who did not have shingles developed dementia.
After adjusting for other health conditions such as diabetes, cancer, and traumatic head injury, the scientists discovered that people with shingles had a 7% lower risk of dementia than people who did not have shingles.
“We were surprised by these results,” said Schmidt. “The reasons for this decreased risk are unclear, but it could be explained by missed diagnoses of shingles in people with undiagnosed dementia. Shingles vaccination is encouraged for older people because it can prevent complications from the disease, but our study suggests it is unlikely to reduce dementia risk.”
Researchers did find that people who had shingles that had spread to the central nervous system had nearly twice the risk of developing dementia. However, Schmidt said such complications are rare, affecting below 0.1% of those with shingles.
A limitation of the study was that participants were identified based on antiviral prescriptions or hospital visits for the disease so results may not be the same for people with milder cases and those who are not treated for the disease.
Reference: “Incident Herpes Zoster and Risk of Dementia: A Population-Based Danish Cohort Study” by Sigrun Alba Johannesdottir Schmidt, Katalin Veres, Henrik Toft Sørensen, Niels Obel and Victor W. Henderson, 8 June 2022, Neurology.
The study was supported by the Edel and Wilhelm Daubenmerkls Charitable Foundation.