The term dementia is nonspecific. It is a term used to describe a group of symptoms associated with a decline in memory or other thinking skills. Dementia can be reversed if it is caught early enough. You have to attend to all the factors that affect brain function. This includes diet, exercise, stress, nutritional deficiencies, toxins, hormonal imbalances, and inflammation.
In the case of most progressive dementias, including Alzheimer's Disease, there is no cure and no treatment that slows down the progression of it. There are drug treatments that can temporarily alleviate symptoms. Dementia is irreversible when it is caused by degenerative diseases or trauma, but might be reversible in some cases when caused by drugs or alcohol. It may also be caused by hormone or vitamin imbalances or depression.