Severe infections are associated with a higher risk of developing dementia, regardless of the presence of other coexisting illnesses, according to a study published March 24 in PLOS Medicine by Pyry Sipilä and colleagues from the University of Helsinki.
The findings are significant because they suggest that infections themselves may play an independent role in increasing dementia risk, rather than simply being linked through shared underlying health conditions. This could influence future prevention strategies for dementia.
Researchers analyzed nationwide Finnish health registry data involving more than 62,000 people aged 65 or older diagnosed with late-onset dementia between 2017 and 2020. They compared these individuals to over 312,000 matched controls without dementia. The study examined all hospital-treated diseases recorded during the previous twenty years and identified 29 diseases strongly linked to increased dementia risk. Of these, two were infections: cystitis (a urinary tract infection) and bacterial infection at an unspecified site. Nearly half of those who developed dementia had at least one of the identified diseases before their diagnosis.
After adjusting for all non-infectious diseases related to dementia, researchers found that the association between both types of infection and later development of dementia remained strong. Less than one-seventh of the excess risk among people with hospital-treated cystitis or bacterial infections was explained by pre-existing conditions. The connection was even stronger for early-onset cases (diagnosed before age 65), where five types of infection—including pneumonia and dental caries—were linked to elevated risk.
The authors said that limitations included lack of baseline cognitive assessments prior to diagnosis and missing data on how infections were treated. "Overall, our findings support the possibility that severe infections increase dementia risk; however, intervention studies are required to establish whether preventing or effectively treating infections yields benefits for dementia prevention," they say.
"Ideally, intervention trials should examine whether better infection prevention helps reduce dementia occurrence or delay the onset of this disease," they add.
