The memory hub was smaller in older adults whose cortisol stayed high
Cortisol stayed high across five years in some older adults. Their hippocampus was smaller and their memory scores worse. Nothing here shows the cortisol caused it.
What the study found
Five years of high cortisol tracked with a smaller memory centre
Older adults whose cortisol stayed high across five years had a measurably smaller hippocampus, the brain's memory hub, than those whose cortisol was normal, and did worse on the memory tasks that depend on it. The more cortisol they had accumulated, the more shrinkage showed.
The caveat · Ageing or illness could drive both
The group was small and elderly, and the published summary never says how many people were in it. In humans this is a correlation; the evidence that cortisol itself damages the structure comes from the rat work the same paper cites. Ageing or illness could equally shrink that structure and raise cortisol at once, which would draw this same pattern with no link between them.