Why you don't have to worry (too much) about Alzheimer's if you have shingles

Life is the result of a complicated balance, and what saves us one moment can kill us the next. A recent study shows that the tau protein protects against neuronal damage caused by herpes simplex virus (HSV-1), and a similar function 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 neurons they initially protected. This long-term accumulation of amyloid plaques and tau tangles is one of the leading hypotheses to explain Alzheimer's disease, although its origin is not solely due to infections and not solely due to this mechanism.

Decades of Alzheimer's research and tens of billions of euros of investment have failed to find an effective treatment. So many years of setbacks have increased interest in alternative interpretations of the origins of the disease, hoping that a new understanding will lead to new solutions. A few days ago, a team from the pharmaceutical company Gilead suggested that preventing herpesviruses as a way to reduce the risk of dementia should be considered a public health priority.

The scientists based their opinion on an analysis of US health databases to observe the relationship between the cold sore virus (HSV-1) and Alzheimer's. Based on data from nearly 700,000 people, they observed that infection is associated with an increased risk of Alzheimer's, that this risk increases with age, and that the use of antivirals reduces the likelihood of developing dementia. However, they acknowledged that further studies are needed and that this correlation does not necessarily imply that herpes causes Alzheimer's and that antivirals prevent it. Along similar lines, a few weeks earlier, the journal Nature published another study that found a correlation between vaccination against herpes zoster, the well-known shingles virus, and a 20% reduction in the risk of Alzheimer's.

Despite the interest of these associations, Alzheimer's remains a very complex disease, triggered by the combination of many linked factors, and a viral explanation is not going to be a panacea. Ignacio López-Goñi, Professor of Microbiology at the University of Navarra, points out that "80% of the population has had herpes, and the percentage of the population with antibodies to herpes simplex is very high." In addition to something as common as being infected with a virus, many other things must 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 preventative measures such as vaccines or antivirals.

In the development of Alzheimer's, as in cancer, countless factors intervene, some of which are innate and others related to lifestyle. Often, disease prevention consists of mitigating the burden of what cannot be changed by acting on what can be modified. Alberto Rábano, director of the CIEN Foundation Tissue Bank in Madrid, points out that, in recent years, although there are increasing cases of Alzheimer's due to an aging population, the incidence has decreased by 16% in the last decade despite the absence of drugs. "This has happened because many cardiovascular risk factors, such as cholesterol, hypertension, diabetes, and tobacco use, are related to Alzheimer's." "What's good for the heart is good for the brain, and preventing cardiovascular health risks has reduced the incidence of Alzheimer's," agrees 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 65 and older, as well as for vulnerable individuals, such as those with hematological diseases or who have received a bone marrow transplant. However, as in the case of cardiovascular diseases, the reduction in the incidence of Alzheimer's would occur as a side effect of other public health measures that are valuable in their own right. However, Argimon does believe that "brain health should be prioritized." “Now, if you ask someone how you can prevent a heart attack, they'll probably know, but if you say the same thing about Alzheimer's, they'll shrug,” he says.

Despite studies linking herpes infections and Alzheimer's, Rábano points out that the Lancet Standing Committee's periodic reference publication on the prevention, intervention, and care of dementia does not include infections among the preventable factors for this type of disease. "They estimate that if all these factors [which include physical inactivity, hearing loss, depression, or a low level of education] were controlled, the incidence of dementia, and especially Alzheimer's, could be reduced by 45%," Rábano points out. However, this committee still considers the evidence on infections to be contradictory.

While the relationship is confirmed and the importance of infections in the onset of Alzheimer's is evaluated, and while drugs are finally being sought that have a significant impact on the disease, the factors that modify the risk of Alzheimer's are a guide to a healthy lifestyle that can be used to prevent or delay almost all ailments. It is known, for example, that the consumption of processed red meat , such as sausages, is associated with a higher risk of dementia, but also of cancer. Ultra-processed foods, when they exceed 30% of the diet, increase the risk of depression, and depression increases the risk of Alzheimer's. Conversely, exercise protects against dementia, but also against cardiovascular disease and cancer, just as a good network of friends or family does. Alzheimer's is a disease as complex as life itself, and delaying its onset depends on as many subtle and interconnected factors, although partly known, as those required for a good life.