Infection That Causes Cold Sores Could Be Linked To Alzheimer’s, Study Suggests

A new study published in BMJ suggests that the herpes simplex virus type 1 could have a role in the development of Alzheimer’s disease.

Herpes simplex virus type 1, also known as HSV-1, is a common virus that causes cold sores.

This new research follows previous studies suggesting a link between HSV-1 and Alzheimer’s disease.

However, experts have called for more research to better understand the findings. Read on to find out more about what we still don’t know around infections and Alzheimer’s risk.

In this new research, scientists examined medical records from over 300,000 people aged 50 and over, splitting them into two equally numbered groups: those who had been diagnosed with Alzheimer’s disease, and those who had not.

The two groups were carefully matched by age, sex, region, and frequency of healthcare visits to ensure fair comparison.

The researchers then looked at whether those with a history of HSV-1 infection were more likely to go on to develop Alzheimer’s.

A total of 1,507 (0.44%) people diagnosed with Alzheimer’s disease had a history of HSV-1 infection, compared with 823 (0.22%) without an Alzheimer’s diagnosis.

People who had an HSV-1 infection had an 80% increased risk of Alzheimer’s, even when other factors, like carrying two copies of the APOE4 gene – a known risk factor for Alzheimer’s – were taken into account.

Using the health record data, the researchers found that people who had taken medication to treat the virus were 17% less likely to develop Alzheimer’s compared with those not taking any medication.

However, there are limitations with this study, and Dr Sheona Scales, Director of Research at Alzheimer’s Research UK explains more: “Despite the large sample size, this research is based on information gathered from using health records and administrative claims data, which often are based on people self-reporting their conditions. Most people infected with HSV-1 don’t have any symptoms so some infections might not have been recorded. Infections predating the information recorded are also not available. Although cases were matched with controls, diagnosing Alzheimer’s disease, especially in the early stages, remains a challenge.”

The authors state that medicines used to treat HSV-1 infections could protect people from developing Alzheimer’s disease, but a lot more work needs to be done to explore this. And we still don’t know why viral infections could lead to a higher risk of someone developing Alzheimer’s.

Researchers are still trying to build more of a picture around how infections could be contributing to an increased risk of developing Alzheimer’s and other types of dementia. One of the reasons could be that infections are causing inflammation in the brain, potentially causing damage. But at the moment, there’s still a lack of understanding around this link.

Dr Scales explains further: “We know there are 14 lifestyle and environmental risk factors for dementia, and there’s not enough evidence to include infections in this list. This study doesn’t tell us if infections are causing the risk, it only shows an association. Further research is needed to understand what the underlying biology around this is.”