Getting sick often feels terrible in the moment, but recent research suggests that severe infections may have longer-term effects on our brain health.
A new study published in Nature Aging adds to growing evidence that serious infections—like the flu, herpes, and respiratory tract infections—are linked to faster brain shrinkage (or atrophy) and a higher risk of developing dementia later in life. This research also offers insights into the biological reasons why infections could contribute to neurodegenerative diseases like Alzheimer’s.
According to experts, this study marks an important step forward in understanding the connection between infections and dementia. While earlier research had already pointed to a link between infections and Alzheimer’s disease, this new study offers a more detailed look at how infections may lead to brain changes that affect memory and thinking abilities.
Interestingly, other studies have shown that vaccines for the flu and shingles (a condition caused by the herpes virus) can reduce the risk of dementia in those who receive them. This highlights the importance of vaccinations not just for protecting against infections but also for preventing the long-term effects these infections may have on brain health.
Severe Infections and Brain Health
The idea that infections can affect brain health isn’t new, but this study provides clearer evidence that infections can have long-lasting effects on cognitive function. Even mild infections can alter our thinking and behavior temporarily, while more severe infections can lead to short-term confusion or delirium, which may be linked to long-term cognitive problems.
As infection severity increases, so does the immune system’s response. According to the study, a strong immune response to a severe infection can have negative effects on the brain. Although the idea that infections could play a role in neurodegenerative diseases has been around for some time, it wasn’t widely accepted. However, the COVID-19 pandemic brought this hypothesis into the spotlight, as long-term cognitive issues, often referred to as “long COVID,” became a more visible concern.
Research now suggests that the connection between infections and brain health is not limited to just one type of infection, whether it be bacterial or viral. In other words, different kinds of infections may all contribute to cognitive decline in some way.
What the Study Found
To investigate this link, researchers used data from the Baltimore Longitudinal Study of Aging, one of the longest-running studies on aging in the U.S. They tracked brain volume changes in nearly 1,000 adults who were cognitively normal, both with and without a history of infection, using repeated brain scans starting in 2009. About 43% of participants had no history of infections.
The researchers examined 15 types of infections and found that six of them—including the flu, herpes, respiratory tract infections, and skin infections—were linked to faster brain atrophy. The brain shrinkage was especially noticeable in the temporal lobe, an area crucial for memory and often affected in Alzheimer’s disease.
The results showed that infections are not only linked to brain atrophy but also to an increased risk of dementia. Using data from the UK Biobank, which included nearly half a million people, and a Finnish dataset with over 270,000 subjects, the researchers found that individuals with a history of infections had a higher risk of developing Alzheimer’s disease years later. The risk was even greater for vascular dementia, the second-most-common form of dementia after Alzheimer’s, which is caused by reduced blood flow to the brain.
How Are Infections and Dementia Connected?
While the connection between infections and dementia is becoming clearer, scientists are still trying to understand the biological mechanisms behind it. The immune system seems to play a significant role. In the study, participants who had a history of infections also showed changes in certain proteins related to the immune system.
Out of 942 proteins examined, 260 were found to be linked to infections, and 35 of these proteins were also associated with changes in brain volume. Some of these proteins appeared to be harmful, contributing to brain atrophy, while others seemed to offer some protection.
In general, infections were associated with an increase in harmful proteins and a decrease in protective ones. This could mean that infections either reduce the brain’s ability to protect itself, or that some form of brain protection was lacking from the start. Although the exact biological processes are still unclear, this study sheds light on potential pathways that might explain how infections increase the risk of dementia.
However, researchers emphasize that this study shows only correlations between infections, immune-related proteins, and brain health. It doesn’t prove that infections directly cause dementia. The study also doesn’t explore how key markers of Alzheimer’s, such as amyloid beta plaques and tau tangles, fit into this link between infections and dementia.
Another important point is that the data was drawn from patients who had been hospitalized for their infections, meaning these were likely more severe cases. Minor infections shouldn’t be a major cause for concern, as previous research suggests they only slightly increase dementia risk. In contrast, infections that require hospitalization nearly double the risk of dementia.
How to Reduce Your Risk of Dementia
Experts advise that preventing serious infections is crucial for maintaining both short-term and long-term health. The 2024 Lancet Commission report on dementia highlights 14 modifiable risk factors that account for nearly half of all dementia cases. These include lifestyle changes like staying socially active, limiting alcohol consumption, and addressing hearing loss.
One of the most effective ways to lower the risk of both severe infections and dementia is through vaccination. Getting vaccinated against the flu and COVID-19 can significantly reduce the risk of complications, hospitalizations, and deaths. The Centers for Disease Control and Prevention (CDC) also recommends the Respiratory Syncytial Virus (RSV) vaccine for everyone over 75 and for those over 60 who are at higher risk of severe RSV. The CDC expects around 800,000 hospitalizations from flu, COVID-19, and RSV this year alone.
In addition, the CDC recommends that everyone aged 50 and older receive two doses of the shingles vaccine, which can also help reduce the risk of dementia. Beyond vaccinations, other preventive measures like wearing masks and washing hands regularly can help lower the risk of infections.