Memory and Exercise

When I continued to look at my topic of the benefits of exercise on the brain, I used the google timeline to narrow my search. I was able to determine when this line of thought was at its peak (in July of 2008). In 2008, there were many studies done that confirmed exercise has many benefits on the brain. In one article in the New York Times, they cited a new study that showed, with "3,485 healthy men and women older than 55 found that those who were physically active three or more times a week were least likely to become cognitively impaired." (http://archinte.ama-assn.org/cgi/content/short/170/2/186?home).
I read another article that said daily exercise may slow the onset of Alzheimer's Disease. They found that those who have symptoms of Alzheimer's and who exercise regularly have four times less brain shrinkage than those who do not hit the pavement. (http://news.injuryboard.com/physical-fitness-may-slow-down-alzheimer%E2%...) One doctor says this makes sense because exercise boosts blood flow in the brain and increases growth hormones. However Dr. Burns also mentions that this increase in blood flow also increases cognitive ability.