As the world’s population continues to age, the risk of dementia is also growing. Finding and evolving ways to prevent the disorder are a focus of researchers. One perhaps surprising way to possibly reduce the risk of dementia is through routine adult vaccinations. The results of a new study, recently published in Nature, show the strongest evidence yet that a vaccine can lower the risk of dementia.

What the study showed

Led by Stanford Medicine, researchers analyzed the health records of older adults in Wales and found that those who received the shingles vaccine were 20% less likely to develop dementia over the next seven years than those who did not receive it.

Previous research has shown that those who get vaccinated against common viruses, including flu, shingles, pneumonia, and tetanus and diphtheria, with or without pertussis, have been associated with a reduced risk for dementia. One theory some experts have is that infections may have an impact on the nervous system and brain, either through inflammation or other neurological complications, which can contribute to cognitive decline.

The data collected from this most recent study supports this theory. With further confirmation, these findings illustrate that the shingles vaccine and other routine vaccinations could be used as a preventive measure for dementia.

What’s different about this study

The results from this latest study are unique because previous research based on health records linking vaccines with lower dementia rates could not account for a major source of bias: People who are vaccinated also tend to be more health-conscious in many ways that are hard to measure. This includes specific behaviors that are known to lower the risk of the disease, such as diet and exercise, but this information is not included in health records.

This research is promising because it evolved from a natural experiment which bypasses the bias. A shingles vaccination program began in Wales on Sept. 1, 2013. The program specified anyone who was 79 on that date was eligible for the vaccine for one year; the following year those who turned 79 would be eligible for one year and so on. People who were 80 years or older would never become eligible for the vaccine.

While these rules were created to ration the limited supply of the shingles vaccine, the circumstances created as close to a randomized controlled trial without conducting one.

Researchers looked at the health records of more than 280,000 older adults who were 71 to 88 years old and didn’t have dementia at the start of the vaccination program. By focusing their analysis on those closest to either side of the eligibility threshold, it allowed them to compare people who turned 80 in the week before with those who turned 80 in the week after. It’s likely that the same proportion of both groups would have wanted to get the vaccine. But because of the eligibility rules, only half of those almost 80 were able to get it.

To provide further validation of this research, the next step would be a large, randomized controlled trial, which would provide the strongest proof of cause and effect.

The big picture about vaccines

While research will continue to identify the correlation between routine adult vaccinations and protecting brain health, it’s important to also remember the broader implications when deciding about whether to get vaccines.

In addition to individual protection and prevention, vaccines also contribute to community health. When a large portion of the population is vaccinated, it creates herd immunity, making it less likely for the virus to spread. This is particularly important for protecting those who cannot be vaccinated, such as infants under six months or individuals with certain medical conditions. Vaccination efforts contribute to a safer environment for everyone.