Dementia can be due to numerous things. Keep in mind, too, that there are different causes of dementia:
-Alzheimer's disease is one of the most common forms of dementia. Alzheimer's disease is characterized by a literal reversal of normal development. The first thing you lose is your judgement skills. The last thing you lose (if you live long enough) is the ability to smile.
-Vascular dementia is another common form of dementia. This is caused by one or more strokes, including small strokes that the patient may not even realize they have experienced. The clinical course of vascular dementia can vary widely because it will depend on the parts of the brain that have been affected.
-Frontotemporal lobe dementia tends to affect younger people (usually in their 50s). This cause a loss of judgement skills and inhibition, and may cause early personality changes.
-Lewy body dementia, relatively rare, causes problems such as hallucinations and parkinsonism (tremors and rigidity similar to those seen in people with Parkinson's disease).
-Mixed dementia occurs when people have more than one type of dementia together.
Again, as already stated, these habits lower risk. They don't necessarily eliminate it. In fact, one of the best ways to lower your children's risk for dementia is to read to them. I recognize that many here are already grands, but you can encourage your children to read to your grandchildren (or read to your grandchildren yourself). This seems to be protective against dementia later in life.
Definitely, keeping mentally active also helps a lot. Keep in mind, too, that just because you may have a "senior moment" or develop "hereafter syndrome" (i.e. you go somewhere and go, "Now what am I here after?"), you may not have dementia. In order for dementia to be diagnosed you must have impairment in memory AND at least one other cognitive domain. Losing your car keys is one thing. Forgetting the way to the grocery store where you've been shopping for 30 years is something else again.