Study Finds Link Between Severe Infections and Dementia

Do serious infections increase the risk of developing dementia on their own, or is that risk actually due to other health conditions that often occur alongside infections? A new study published in PLOS Medicine shows that preventing infections may play a role in protecting long-term brain health.

A team of investigators from Finland analyzed nationwide health data from more than 62,000 adults aged 65 and older who were diagnosed with dementia between 2017 and 2020, comparing them with more than 300,000 similar individuals without dementia. They looked back over a period of up to 21 years to identify medical conditions people had before developing dementia.

The study found that many different health conditions, 29 in total, were linked to a higher risk of dementia. These included a wide range of illnesses, such as mental health conditions, heart and metabolic diseases, neurological disorders, digestive issues and even injuries. Nearly half (47%) of the people who developed dementia had at least one of these conditions beforehand, showing how interconnected overall health and brain health can be.

“We found 27 diverse severe, hospital-treated diseases that were robustly associated with an increased risk of dementia,” investigators said.

Importantly, the team focused on two types of infections: urinary tract infections (including cystitis) and other serious bacterial infections. Even after accounting for all the other health conditions that could influence dementia risk, these infections were still linked to an increased risk of developing dementia. In other words, the connection between infections and dementia could not be explained away by other illnesses.

For patients, this suggests that serious infections may play an independent role in long-term brain health. While the increase in risk was modest (about 19% to 22% higher), it was consistent across different groups, including men and women and people with different education levels. The link was even stronger in people who developed dementia at a younger age.

However, it’s important to understand what this study does (and does not) show. Because it is observational, it cannot prove that infections directly cause dementia. There may still be other factors involved, such as lifestyle, immune system health or access to care, that were not captured in the data. The team said unmeasured confounding factors may have also affected the results.

Still, the study has several important strengths that make its findings more reliable. It included a very large number of people from across Finland, which helps ensure the results are accurate and not due to chance. The team also looked broadly at many different health conditions over a long period, up to 20 years before a dementia diagnosis, rather than focusing only on a few known risk factors. This wide approach allowed them to identify connections that may not have been recognized before. In addition, the study used medical records instead of relying on people to remember and report their own health history, which helps reduce errors or bias in the data.

The findings highlight a key takeaway: Preventing and properly treating infections may be more important than we realize — not just for short-term health, but potentially for long-term brain health as well. It also reinforces the importance of managing overall health, since many conditions appear to work together to influence dementia risk.

Investigators said further research is needed to determine whether reducing infections could actually lower the number of dementia cases, but this study adds to growing evidence that protecting your body may also help protect your brain.

“In our study, dementia-related infections occurred on average 5 to 6 years before dementia diagnosis,” investigators noted. “Given that the development of dementia often takes years or even decades, these findings suggest that severe infections might accelerate underlying cognitive decline.”