THURSDAY, March 26, 2026 (HealthDay News) -- The increased risk for dementia seen in association with infectious diseases is not attributable to comorbid dementia-related diseases diagnosed before infections, according to a study published online March 24 in PLOS Medicine.
Pyry N. Sipilä, M.D., Ph.D., from the University of Helsinki, and colleagues examined the role of noninfectious mental and physical illnesses in the association between severe infections and dementia. The study included 62,555 individuals aged 65 years or older in Finland who were diagnosed with late-onset dementia and 312,772 matched dementia-free controls.
The researchers identified 29 hospital-treated diseases that occurred one to 21 years before dementia diagnosis in cases (or index date in controls) and were associated with increased dementia risk (adjusted rate ratio, 1.20). Two were infectious diseases (cystitis and bacterial infection of an unspecified site) and 27 were mental, behavioral, digestive, endocrine, cardiometabolic, neurological, and eye diseases, as well as injuries. Overall, 47 percent of the dementia cases had at least one of these diseases diagnosed prior to dementia. The associations between the two infectious diseases and dementia risk were not attributable to the 27 comorbid dementia-related diseases. The rate ratio for cystitis was 1.22 and 1.19 before and after adjustment for comorbidities, respectively, and for bacterial infections of an unspecified site, the rate ratio was 1.21 and 1.19, respectively. Across subgroups defined by sex and education, the findings were comparable and were stronger for cases of early-onset dementia.
"Given that the development of dementia often takes years or even decades, these findings suggest that severe infections might accelerate underlying cognitive decline," the authors said in a statement.