People who are fit have a lower risk of developing Alzheimer's disease than people who are less fit, the American Academy of Neurology studies show. A study by experts at Washington Medical Center found that as people become more physically fit, their risk of Alzheimer's disease decreases. This means that people can work on gradual changes and improvements in their physical fitness and reduce their risk of the serious disease. The study, led by Edward Zamrini, M.D., included 649,000 military veterans with an average age of 61. The average follow-up period was nine years. They did not have Alzheimer's disease at the beginning of the study.

Researchers determined participants' cardio-respiratory endurance to understand how well the body carries oxygen to the muscles and how well the muscles can absorb oxygen during exercise. Participants were divided into 5 groups based on fitness level. The fitness level was determined by how well the participants did on the treadmill test. Middle-aged and older people could achieve the best fitness level by actively walking for 2.5 hours per week. In the group with the lowest level of physical fitness, Alzheimer's disease developed at a rate of 9.5 cases per 1,000 person-years, compared with 6.4 cases per 1,000 person-years in the healthiest group. The incidence rate decreased as fitness level increased: 8.5 for the second least fit group, 7.4 for the average group, and 7.2 for the second most fit group.