Sasun Bughdaryan
By Stephen Beech
A common infection raises the risk of dementia, warns new research.
Cystitis increases the danger of developing the debilitating condition independently of other ailments and conditions, according to the study.
The urinary tract infection (UTI) is very common, particularly in women, with up to 60% experiencing it at least once in their lifetime.
Data shows around one-in-10 women suffer an annual bout of cystitis.
Severe infections had been previously linked to an increased risk of dementia.
But it had been unclear whether the association could be explained by other non-infectious diseases that predispose people to both infections and dementia.
For the new study, researchers used health registry data from Finland covering more than 62,000 people aged 65 or older who were diagnosed with dementia between 2017 and 2020, along with more than 312,000 matched dementia-free people.
Associations between dementia-related diseases. For clarity, the figure illustrates associations between 14 of the 29 dementia-related diseases identified in the study (all 29 diseases are shown in Fig 4 of the paper in PLOS Medicine). (Sipilä PN, et al., 2026, PLOS Medicine, CC-BY 4.0 via SWNS)
The international team examined all hospital-treated diseases recorded during the previous 20 years, identifying 29 diseases that were "robustly associated" with increased dementia risk.
Nearly half of dementia cases (47%) had at least one of the 29 identified diseases before their diagnosis.
Of those diseases, two were infections: cystitis and bacterial infection of an unspecified site.
Among the non-infectious diseases, the strongest associations with dementia were seen for mental disorders due to brain damage or physical disease, Parkinson’s disease, and alcohol-related mental and behavioural disorders.
When the researchers then adjusted for all 27 non-infectious dementia-related diseases identified, the association between both infections and dementia remained largely intact.
Less than one-seventh of the excess dementia risk among people with hospital-treated cystitis or bacterial infections was attributable to pre-existing conditions, according to the findings published in the journal PLOS Medicine.
Mayra Camargo
The link between infections and dementia was even stronger for early-onset dementia - diagnosed before age 65, where five types of infection - including pneumonia and dental caries—were associated with elevated risk.
Study leader Pyry Sipilä, of the University of Helsinki in Finland, said: “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.
"We found 27 diverse severe, hospital-treated diseases that were robustly associated with an increased risk of dementia.
"Two of these diseases were infections, namely urinary tract infections and unspecified bacterial infections.
“In our study, dementia-related infections occurred on average five to six years before dementia diagnosis.
"Given that the development of dementia often takes years or even decades, these findings suggest that severe infections might accelerate underlying cognitive decline.
"However, as these findings were observational, we cannot exclude the possibility that some unmeasured confounding factors might also have affected our findings. Thus, we cannot prove cause and effect.”
He added: “Ideally, intervention trials should examine whether better infection prevention helps reduce dementia occurrence or delay the onset of this disease.”
