The problem with dementia, is that, like cancer or heart disease, it is a compendium term that covers a wide range of illnesses with a shared symptom. It has elements that are genetic, environmental, associated with our chosen life style, the result of problems much earlier in life, accidents of life and many other causes.
Like cancer, doctors can only treat the symptoms, and in the case of dementia there is not much they can do. When it comes to prevention all doctors can do is tell us what we can do to reduce our chances of getting either disease. All we can do is follow their guidelines and hope for the best.
The research team that can find a way of banishing these diseases from human life as we have almost done with polio will get Nobel Prizes galore, but I am not sure that it will ever be possible.