People who are conscientious and prone to "doing the right thing" are less likely to develop Alzheimer's disease as they age, according to a long-running study of Catholic nuns, priests and brothers. This trait is about self-discipline and delayed gratification. Related reports have noted that people who suppress their rage rather than venting it are more likely to die young, and that more years of schooling preserves cognitive function. It was also found that people who don't complete high school are more likely to develop dementia and Alzheimer's disease than those with more education. Go figure.
I've also read before that people who are life-long learners and strive to add new skills to their repertoire consistently are less likely to develop Alzheimer's and also less likely to develop other neurological disorders associated with aging, which makes sense if the brain is a muscle we are meant to exercise.