I have read a book called 'The End of Alzheimers' by Dr Dale Bredesen who is a Professor of Neurology in California. The book explains why there is no cure for dementia and, I'm afraid to say, unlikely to be one. However, it has a protocol of treatment strategies - tailored to the individual, which have had very positive results on patients where he works. The strategies are not straightforward and not fully achievable in the UK without the aid of an unconventionally trained GP (a functional doctor).
But the message is based on looking at your diet, exercise, sleep patterns, baseline blood chemistry, your genes etc - on the basis that a lot of dementias (and other diseases) stem from an inflammatory response which the body is trying to protect itself from, but doing it badly. So, remove or reduce the sources of inflammation and the brain will respond. And starting treatment or prevention as early as possible is also the message.
There are certain things we can all do without medical tests and the book is definitely worth reading just to find out more about dementia itself
