Hopefully this is true, I feel like the studies were not thorough enough to conclude conclusively that Dementia is declining, for example the study in Denmark had relatively moderate to small numbers and takes people at different ages (93 and 95, perhaps people with Dementia likely die before 95 for example). The British study seems better, but still 56% of people declining is kind of high.

In either case, logically this seems fairly strait forward and these studies do provide some insight, so good news! I hope there's a similar study done in the U.S.