My opinion is dementia, is caused by depression, usually brought on by trauma or stress in older age....or life long depression, sadness, or an undercurrent of depression....which the brain cannot bounce back from as one ages. It is loss of cognitive functioning. However, that does not mean loss of feelings or spirit...its loss of mind and body function.
I think it is determined by health and diet in the body.... as how far it progresses for some, and by level of spiritual or emotional health.
In a way, it seems to be a loss of will to function or be happy in the physical life, for many. That doesn't explain all cases, but the ones Ive seen working in health care, I would say the majority.
The spirit health is always #1 in diseases...but the body health is also determined by diet, exercise, stress and other factors, too.
This is my way of not candy coating the subject.
I have my personal beliefs, about why more people suffer dementia these days...than ever before...and I think it's a combination of our poor diets, not living by the laws of nature, and by families not living unified and together in close knit communities where they care for each other like the old days. Now they are in nursing homes, instead of in tribes of families. But, that goes into a whole other subject about how the "system" is set up.