Negative opinion. Two words that are like a guillotine for Alzheimer’s patients. In the middle of summer, experts from the European Medicines Agency closed the door on the arrival on the market of the new generation of treatments available for a few months in the United States. Too risky, for too little benefit. Despite the promises and the billions invested, this disease, which eats away at the brain and erases memories, continues to resist the efforts of scientists and pharmaceutical laboratories. Most of the information concerning Alzheimer’s is more depressing than the last. All the more reason to rejoice in another piece of news, which is confirmed study after study: senile dementia, which includes Alzheimer’s disease and a few other pathologies, can very largely be prevented. Almost half of cases, 45% to be precise, could be avoided in the years to come, according to the latest calculations of a group of 27 international experts commissioned by the scientific journal The Lancet.
A massive challenge, because at the current rate, there will be 153 million sick people in the world in 2050, compared to 57 million in 2019. “When I start a conference, I usually say that by the age of 90, one in three people in the audience will develop dementia,” recalls Professor Philippe Amouyel, epidemiologist and CEO of the Alzheimer’s Foundation. These are dark predictions, but they are therefore not inevitable. Better still, even with an affected parent or grandparenteven with predisposing genes, the most recent research shows that it is possible to greatly reduce the risk of falling ill yourself. “The hundreds of studies compiled in our report for The Lancet “The findings provide a message of hope, confirming that there are already at least 14 risk factors that can be acted upon,” insists Gill Livingston, professor of psychiatry at University College London and lead author of the work.
Preventing dementia? The idea might seem absurd, as this pathology seems to be linked to our inexorable aging. But scientists began to wonder about it several decades ago, noting over time, in certain rich countries, a slight decrease in the incidence of the disease, that is to say the proportion of individuals affected in a given age group. Commonly accepted explanations: the lengthening of the duration of studies for a growing part of the population, and a decline in smoking. An improvement that is difficult to perceive for the general public because it is offset by the increase in the number of elderly people, but all the same: “This has made it possible to consider the possibility of prevention, since the incidence was already decreasing with the natural evolution of certain risk factors”, recalls Philippe Amouyel.
Winning the race against injuries
A finding corroborated by another observation. While the disease is characterized by the accumulation of senile plaques in the brain, which stifle and kill neurons, some individuals, despite carrying these plaques, die without ever having developed the slightest symptom. The challenge would therefore not be so much to prevent the appearance of anomalies, the origin of which scientists are still struggling to understand, as to delay the appearance of the disorders as long as possible. “It’s a bit like there was a race between the impact of these lesions and the brain’s ability to cope with them,” summarizes Professor Bruno Dubois, former head of the neurology department at the Pitié-Salpêtrière hospital and co-author of Alzheimer’s is not inevitablepublished on September 18 (Harper Collins). How, under these conditions, can you put all the chances on your side to try to win this race?
The level of education counts for a lot, but since it has continued to progress, this is no longer where the most significant gains will come from in the future in developed countries. Doctors are now targeting as a priority what they call the “executions of the heart”, that is to say all the cardiovascular risk factors. Because they are also executioners of the brain: “They will have an impact on the quality of vascularization and therefore cerebral oxygenation, itself a determining factor in the more or less early onset of symptoms”, explains Professor Dubois. Measuring and treating high blood pressure, avoiding diabetes and obesity, not smoking, limiting alcohol consumption as much as possible, and this throughout one’s life: these are all known factors on which it is possible to act.
Monitoring the level of “bad cholesterol” (LDL cholesterol) was added to the list this year by the experts at The Lancet. With a key message: although it is never too late, it is ideally from the forties that we should start monitoring and treating it – an age when we are not usually very concerned about the pangs of chronic diseases. “Beyond the effect on the quality of the blood vessels, studies suggest a direct link between an excess of this cholesterol and the deposition of proteins that form senile plaques, even if the exact mechanisms are still poorly understood,” explains Gill Livingston.
Cognitive stimulation
The other great enemy of the brain is of course social isolation and all its causes: depression, but also visual and hearing loss, which tend to cut off those who suffer from it from their environment. Treating them as soon as they appear, regardless of age, reduces the subsequent risk of dementia, even several decades later. “The hypothesis is that cognitive stimulation strengthens synaptic connections between neurons. Our brain is an information processing machine and social interactions provide a huge amount of information,” summarizes Professor Dubois.
Physical activity, whose general health benefits are well-established, must also be encouraged to combat dementia. Because beyond its cardiovascular benefits, it also directly strengthens brain connections. Scientists already know that, at least in rodents, sport has an effect on the myelin sheath that protects these connections. At the Paris Institute of Psychiatry and Neuroscience, Maria Cecilia Angulo has set up a project with the support of the Foundation for Medical Research to go further: “We are going to check whether the same is true in humans, and also see what type of physical activity is most effective,” she explains. With the hope, in the long term, of being able to make ever more precise and relevant recommendations.
While it is possible to act on all of these factors, there is one that is more difficult to protect yourself from on an individual basis: air pollution. There is little doubt about its role in dementia, and not only because of its impact on the cardiovascular system: “It has been proven that fine particles linked to car traffic and wood burning directly damage the brain,” says Gill Livingston. Conversely, various studies have already shown the benefit of LEZs (low-emission zones, where the most polluting vehicles are banned) in protecting the people who live there.
Non-exhaustive list
In the future, the list established by the Lancet experts could be enriched with new parameters. Lack of sleep, an unbalanced diet, infections, mental illnesses are often mentioned, but the scientific evidence is not yet fully there to date. The role of environmental pollutants such as pesticides or PFAS, also called eternal pollutants, is also debated. In France, a team specializing in the epidemiology of neurodegenerative diseases is building a large study to answer this question. “We are working on the exposome, that is to say all environmental exposures: we are going to look in different cohorts for biomarkers of pollutants, and see if there is a link with the onset of dementia,” explains Cécilia Samieri, Inserm research director at the University of Bordeaux.
Will this knowledge really make a difference? “It all depends on how individuals, but also politicians, take hold of it,” says Gill Livingston. The potential of a 45% reduction in the number of cases will only be achieved if all the factors identified are addressed. With always the risk, on an individual level, that these efforts will prove insufficient, since they will not prevent all cases of dementia. “They will not be in vain, however, because the same measures also contribute to the prevention of all other chronic diseases,” argues Gill Livingston. “We can assume that, in all cases, those who succeed in implementing them will live a longer and healthier life.” Isn’t that what we all want?
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