The results of a large Finnish study show that cystitis and serious bacterial infections appear to increase a person’s risk for developing dementia even after correcting for the presence of common health conditions known to increase dementia risk like mental health disorders.
“Growing evidence from observational cohort studies suggests that severe, hospital-treated infections are associated with an increased risk of dementia. Several plausible mechanisms have been proposed to explain this association, including disturbed peripheral-central immune crosstalk, which contributes to neuroinflammation,” write lead investigator Pyry Sipilä, MD, PhD, a researcher at the University of Helsinki, and colleagues in PLOS Medicine.
“However, given its typical late-onset, clinically diagnosed dementia rarely occurs in isolation from other age-related diseases…Many of these diseases also increase the risk of infections.”
To try and assess if infections increase the risk of dementia independently from other health conditions or risk factors linked to the disease, the researchers used national health and population registers in Finland to identify over 62,000 people aged 65 and older who were diagnosed with dementia between 2017 and 2020, and more than 312,000 similar people without dementia for comparison.
Looking back up to 21 years before a diagnosis of dementia, the investigators assessed links between 170 other diseases and dementia. Of these, 29 did show an association with the onset of dementia including mental health problems, cardiovascular and neurological diseases, diabetes, and some digestive and eye diseases. Almost half of all those in the study with dementia had at least one of these conditions before their diagnosis.
Notably, the team found that hospital-treated cystitis and bacterial infection at an unspecified site were linked to dementia and the association remained after adjusting for all 27 noninfectious conditions. After correcting for possible confounding factors, the presence of one of these infections increased the risk for dementia by 19% on average, although the risk was higher for early onset dementia.
“In our study, the average time difference between infection diagnosis and dementia was relatively short, 5–6 years. This time frame suggests that the inflammatory insult resulting from infections severe enough to require hospital treatment may accelerate pre-existing preclinical stage of dementia rather than initiate neurodegeneration in a cognitively healthy person,” suggest the authors.
“Evidence from cohort studies and natural experiments indicates that vaccination against infectious diseases might be an effective strategy for reducing or postponing the onset of dementia.”
As this is observational research, it cannot prove that preventing infections will prevent dementia, note Sipilä and colleagues, but it does strengthen the case for testing if better infection prevention and management might help lower dementia risk or delay its onset.
