A vaccine to fight dementia? It turns out there may already be one – shots that prevent painful shingles also appear to protect aging brains.

A new study found shingles vaccination cut older adults’ risk of developing dementia over the next seven years by 20%.

The research, published Wednesday in the journal Nature, is part of growing understanding about how many factors influence brain health as we age – and what we can do about it.

“It’s a very robust finding,” said lead researcher Dr. Pascal Geldsetzer of Stanford University. And “women seem to benefit more,” which is important as they’re at higher risk of dementia.

The study tracked people in Wales who were around 80 when receiving the world’s first-generation shingles vaccine over a decade ago. Now, Americans 50 and older are urged to get a newer vaccine that's proven more effective against shingles than its predecessor.

The new findings add another reason for people to consider rolling up their sleeves, said Dr. Maria Nagel of the University of Colorado Anschutz Medical Campus, who studies viruses that infiltrate the nervous system.

The virus “is a risk for dementia and now we have an intervention that can decrease the risk,” Nagel said.

With Alzheimer’s and other forms of dementia on the rise in an aging population, “the implications of the study are profound,” Dr. Anupam Jena, a Harvard physician and health economist, wrote in a Nature commentary.

Anyone who’s had ever had chickenpox – nearly everybody born before 1980 – harbors that virus for the rest of their life. It hides in nerves and can break out when the immune system weakens from illness or age, causing painful, blister-like sores typically on one side of the body that last for weeks – what’s called shingles.

About 1 in 3 Americans will get shingles, according to the Centers for Disease Control and Prevention. While most recover, it sometimes causes severe complications. If it infects an eye it can cause vision loss. Up to 20% of shingles patients suffer excruciating nerve pain months or even years after the rash itself is gone.

It’s not clear exactly how Alzheimer’s and other types of dementia form. But certain viruses that sneak inside the nervous system – especially members of the herpes family including the chickenpox virus -- have long been suspected of adding to genetic and other factors that make people more vulnerable.

Last summer, doctors at Boston’s Brigham and Women’s Hospital reported that an episode of shingles could raise someone’s risk of dementia by about 20%.

Partly, it’s because that virus can cause inflammation, bad for organs including the brain. It also can directly infect blood vessels in the brain, causing clots and impeding blood flow, said Colorado’s Nagel, a risk both for strokes and for dementia.

More intriguing, her lab also discovered shingles can spur formation of a sticky protein called amyloid that’s one of the hallmarks of Alzheimer’s.

Adults who get recommended vaccines tend to have other brain-healthy habits including exercising and a good diet, which made it hard to prove an extra benefit.

Stanford’s Geldsetzer took advantage of “a natural experiment” in Wales, which opened shingles vaccinations with an age limit: anyone 80 or older on Sept. 1, 2013, was ineligible but those still 79 could squeeze in. Comparing seniors who just met or just missed that cutoff would mimic a research study that randomly assigned otherwise similar people to be vaccinated or not.

Geldsetzer’s team analyzed more than 280,000 medical records and found evidence that vaccination did offer some protection against dementia. At the time, people received a first-generation vaccine called Zostavax.

An important next step is testing whether today’s vaccine, Shingrix, also offers dementia protection, Nagel said. Another research group recently reported some evidence that it does. Vaccine manufacturer GSK last month announced a collaboration with UK health officials to track seniors’ cognitive health as they get vaccinated.

Geldsetzer also hopes to further study that earlier shot to see if the type of vaccine might make a difference.

Shingrix is a onetime vaccination, given in two doses a few months apart. The CDC recommends it starting at age 50 for most people but also for younger adults with certain immune-weakening conditions – including those who years ago got that first-generation shingles vaccine. Fewer than 40% of eligible Americans have gotten vaccinated.

Side effects including injection-site pain and flu-like fever and achiness are common. The CDC cautions if you’re currently fighting another virus such as the flu or COVID-19, to wait on a shingles shot until you’re well.

While there’s no proven prevention for dementia, doctors also recommend other commonsense steps to lower the risk. Stay socially and cognitively active. And control high blood pressure and, for people with diabetes, high blood sugar, both of which are linked to cognitive decline.