Being social often involves physical exercise or mental activity, which is ideal for preventing Alzheimer's because physical and mental activity are also good for the brain. Great ways to stay socially active include working, volunteering, joining clubs, and traveling, particularly in organized travel groups.
Sources:
Brain health. Alzheimer's Association. October 18, 2007. http://www.alz.org/we_can_help_brain_health_maintain_your_brain.asp
Shankle, W. R., & Amen, D. G. 2004 Preventing Alzheimer's: Ways to help prevent, delay, detect, and even halt Alzheimer's disease and other forms of memory loss. New York: G. P. Putnam's Sons.

