Data from 876 patients (average age 78) in the 30-year Cardiovascular Health Study show that virtually any type of aerobic physical activity can improve brain volume and reduce Alzheimer's risk.
A higher level of physical activity was associated with larger brain volumes in the frontal, temporal, and parietal lobes including the hippocampus, thalamus and basal ganglia. Among those with MCI or Alzheimer's (25% of the participants), higher levels of physical activity were also associated with less brain atrophy. An increase in physical activity was also associated with larger grey matter volumes in the left inferior orbitofrontal cortex and the left precuneus.
Further analysis of 326 of the participants found that those with the highest energy expenditure were half as likely to have developed Alzheimer's disease five years later.
Physical activity was assessed using the Minnesota Leisure-Time Activities questionnaire, which calculates kilocalories/week using frequency and duration of time spent in 15 different leisure-time activities: swimming, hiking, aerobics, jogging, tennis, racquetball, walking, gardening, mowing, raking, golfing, bicycling, dancing, calisthenics, and riding an exercise cycle.
The study does not look at whether some types of physical activity are better than others, unfortunately, but its message that overall physical activity, regardless of type, helps in the fight against cognitive impairment is encouraging.
 Longitudinal Relationships between Caloric Expenditure and Gray Matter in the Cardiovascular Health Study. Journal of Alzheimer's disease: JAD. 2016 .