Dementia is an umbrella term which includes several diseases or conditions which result in a common set of symptoms. Alzheimer's is just one disease which results in dementia. Dementia may also be a result of a stroke or heart failure.
An analysis of the Framingham Heart Study, a multi-decade study to identify factors for heart disease, indicates there has been a decrease in the incidence of dementia over a 30 year period. This is an interesting analysis because it points to improved cardiovascular health leading to improved cognitive function.
Anything that reduces dementia is a good thing!
Good heart = good brain.