Depends. Viral infections yes by good hygiene practices. Genetically derived dementia including alzheimer's can be unpredictable. Curb lifestyle habits including substance abuse.
Prevention. The best way to treat brain injury is prevention. For example, wearing helmets and avoid activities where you may hurt your head. If you are inquiring if there are any natural brain protectants--recent studies have indicated that Progesterone which is a natural hormone has protective effects in head injury.