Why you don’t have to worry (too much) about Alzheimer’s if you have herpes

Life is the result of a delicate balance, and what saves us at one moment can kill us the next. A recent study shows that the tau protein protects against the neuronal damage caused by herpes (HSV-1) infection, and a similar protective role has also been identified for beta-amyloid.

Over time, if the infection persists, both proteins can accumulate in the brain, becoming toxic and destroying the very neurons they initially protected. This long-term buildup of amyloid plaques and tau tangles is one of the leading hypotheses for explaining Alzheimer’s disease —though its origins are not solely due to infections, nor due to this mechanism.

Decades of Alzheimer’s research and tens of billions of investment have failed to find an effective treatment. So many years of setbacks have increased interest in alternative theories about the origin of the disease, in the hope that a new understanding might open the door to new solutions. A few days ago, a team from the pharmaceutical company Gilead suggested that preventing herpesvirus infections as a way to reduce the risk of dementia should be considered a public health priority.

The scientists based their conclusions on an analysis of U.S. health databases to explore the relationship between the herpes simplex virus (HSV-1), which causes cold sores, and Alzheimer’s disease. Drawing on data from nearly 700,000 people, they observed that the infection is associated with a higher risk of developing Alzheimer’s, that this risk increases with age, and that the use of antiviral medication reduces the likelihood of dementia.

However, the researchers acknowledged that further studies are needed and that this correlation does not necessarily mean that herpes causes Alzheimer’s or that antivirals prevent it. Along similar lines, just a few weeks earlier, the journal Nature published another study that found a correlation between vaccination against shingles — also known as herpes zoster — and a 20% reduction in Alzheimer’s risk.

Despite the interest these associations have generated, Alzheimer’s remains a highly complex disease, triggered by the interplay of many interconnected factors, and the viral explanation is unlikely to be a silver bullet. Ignacio López-Goñi, professor of Microbiology at the University of Navarra in Spain, points out that “80% of the population has had herpes, and the percentage of people with antibodies to herpes simplex is very high.” In addition to something as common as contracting a virus, many other things need to happen for Alzheimer’s to develop.

“People who carry a variant of the APOE gene are more susceptible to Alzheimer’s disease and to herpes reactivation and its neurodegenerative effects,” López-Goñi points out.

Therefore, those with a genetic predisposition or weaker immune systems — such as older adults — may benefit more from preventive measures like vaccines or antiviral treatments.

In the development of Alzheimer’s — just like in cancer — countless factors come into play, some of them innate and others related to lifestyle. Often, preventing the disease involves reducing the impact of what cannot be changed by acting on what can.

Alberto Rábano, director of the CIEN Foundation Brain Bank in Madrid, points out that although Alzheimer’s cases have risen in recent years due to an aging population, the incidence has actually dropped by 16% over the past decade despite the lack of effective drugs. “This has happened because many cardiovascular risk factors, such as cholesterol, hypertension, diabetes, and tobacco use, are related to Alzheimer’s,” he explains.

“What’s good for the heart is good for the brain, and preventing cardiovascular health risks has reduced the incidence of Alzheimer’s,” says Josep Maria Argimon, director of Relations with the Healthcare System at the Foundation and the Barcelonaβeta Brain Research Center.

Argimon believes that “there is increasing evidence indicating that herpes simplex or shingles infections, as indicated by the vaccine study, could contribute to the onset of the disease.” But, he adds: “There is no demonstration of causality and no evidence to support the idea of mass vaccination against herpes as a way to prevent Alzheimer’s.”

For now, in countries like Spain, vaccination has begun for people aged 65 and over, as well as for vulnerable individuals such as those with blood disorders or who have undergone bone marrow transplants. But, as with cardiovascular diseases, a reduction in Alzheimer’s incidence would be a secondary effect of other public health measures that are valuable in their own right.

Nevertheless, Argimon believes that “brain health should be prioritized.” “Today, if you ask someone how to prevent a heart attack, they’ll likely know the answer, but if you ask the same about Alzheimer’s, they’ll just shrug,” he says.

Despite studies linking herpes infections to Alzheimer’s disease, Rábano notes that in the landmark publication regularly issued by The Lancet Commission on the prevention, intervention, and care of dementia, infections are not included among the preventable risk factors for such diseases. “They estimate that if all these factors [which include physical inactivity, hearing loss, depression, or low educational attainment] were controlled, the incidence of dementia — mainly Alzheimer’s — could be reduced by 45%,” Rábano points out. However, the commission still considers the evidence regarding infections to be contradictory.

While the connection is confirmed and the role of infections in the development of Alzheimer’s is assessed — and as researchers continue to search for drugs that finally have a meaningful impact on the disease — the factors that modify Alzheimer’s risk offer a roadmap for a healthy life that helps prevent or delay nearly all illnesses.

For example, it is known that consumption of processed red meats, such as cold cuts, is linked to a higher risk of dementia, as well as cancer. Ultra-processed foods, when they make up more than 30% of the diet, sharply increase the risk of depression — and depression, in turn, raises the risk of Alzheimer’s.

On the other hand, exercise protects against dementia, as well as cardiovascular disease and cancer — just like having a strong network of friends or family does. Alzheimer’s is a disease as complex as life itself, and delaying its onset depends on countless subtle, interconnected factors — many of which are at least partially understood — just like those needed for a good life.

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