Herpes Zoster May Reduce Dementia Risk

Despite scientific speculation that inflammation may increase risk of dementia, a new study published in Neurology has found that herpes zoster is not associated with an increased risk of dementia. 

“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. “Herpes zoster 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.”
 
Data for this study came from Danish medical registries over a 20-year period for 247,305 people who visited a hospital or were prescribed antiviral medication for herpes zoster and 1,235,890 people who did not have the disease. These individuals were an average age 64.
 
Up to 21 years later, 9.7% of those with vs 10.3% of those without herpes zoster developed dementia. After adjustment for confounding comorbid conditions (traumatic head injury, diabetes, or cancer), those who had herpes zoster had a 7% lower risk of dementia.

“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 herpes zoster in people with undiagnosed dementia. Vaccination for herpes zoster is encouraged for older people because it can prevent complications from the disease, but our study suggests it is unlikely to reduce dementia risk.”
 
Among those who had herpes zoster spread to the central nervous system there was nearly twice the risk of developing dementia, but that was rare (<0.1%).
 
A limitation of the study is that data came from individuals with hospital visits or prescriptions for herpes zoster, which may not occur in mild cases, these results may be subject to selection bias.