In a world where everything is accelerating and where daily stress is more and more intense, health indicators quickly turn into the red if we do not learn to manage stress, whether by sleeping well, by practicing relaxation techniques or regular physical activity. So much so that we wonder what the real impact of stress is on our brain. For the first time, Sudha Seshadri's team from the University of Texas at San Antonio evaluated it in healthy humans: stress reduces brain size and impairs cognitive functions, including memorization. .
The first effect of stress on our body is the activation of a nervous and hormonal axis, called the hypothalamic-pituitary axis. This results in the secretion of the main stress hormone, cortisol; its action in combination with other molecules allows the body to react and adapt - at best. In laboratory animals and in small groups of people, often elderly or suffering from pathologies, various scientific studies have shown that high concentrations of blood cortisol are associated with changes in certain structures of the brain and sometimes with cognitive alterations. However, the results are often contradictory, and no study has looked at large numbers of young and healthy people.
This is what Seshadri and his colleagues did thanks to participants and data from the Framingham Heart Study cohort: more than 2,200 people aged on average 48.5 years old, not suffering from any neurological or psychiatric disorder, underwent measurements of their fasting blood cortisol level in the morning, before having a brain MRI as well as cognitive tests (among other examinations). The results revealed that the subjects' average blood cortisol concentration was 12.92 micrograms per deciliter, with one third of the participants having a low level (less than 10.8), one third having a high level (greater than 15.8). ), the last third being between the two. But above all, the most stressed people have a smaller brain than that of the other two groups, with in particular less gray matter (formed by all the cell bodies of neurons) in the frontal and parietal cortices (involved in particular in the functions such as planning, inhibition and spatial orientation). People with elevated cortisol levels also have a greater alteration of white matter, made up of extensions of neurons and involved in the transmission of information. And these structural changes are accompanied by cognitive deficits: the most stressed people do less well on memorization and attention tasks. The effects are greater in women than in men, perhaps because they are generally more "sensitive" to the glucocorticoid hormones, including cortisol. Stress therefore already affects the brains of middle-aged, healthy people, that is to say long before the first signs of brain aging and possible pathologies.
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