Numerous studies have found an association between physical activity and later cognitive performance, but most have relied on self-reported activity. A recent study tried to get a more precise picture of the relationship between physical activity and later cognitive performance by using accelerometers to directly measure physical activity.
Researchers gave 6,452 older adults with an average age of 70 an accelerometer to wear during all waking hours for a week, and three years later tested participants on cognitive impairment, executive function, and memory. They categorized the accelerometer data into moderate-to-vigorous physical activity, light-intensity physical activity, and sedentary activity. This large cohort had the advantage of being 30 percent black, which allowed racial differences to be explored.
On average, participants spent only 1.5 percent of their time doing moderate-to-vigorous activity. The participants in the bottom 25 percent of moderate-to-vigorous activity spent only half a minute per day doing this type of physical activity, compared to the top 25 percent spending an average of 20 minutes per day. Overall, on average 77 percent of participants’ time was sedentary, and 21 percent was spent doing light-intensity activity.
Three years later, the researchers found that those individuals who had done the most moderate-to-vigorous physical activity showed a 36 to 47 percent lower risk of cognitive impairment, and exhibited less change in memory and executive function. This result remained when age, sex, race, and education were taken into account statistically. No such associations with cognition were found for the percentage of time spent doing light physical activity, which suggests that intensity of exercise matters to achieve cognitive benefits.
Looking at black participants separately, the impact of moderate-to-vigorous activity was only associated with better memory scores. Additional research is needed to determine the reasons for these observed racial differences.
The precise nature of this data allowed the researchers to determine that even a small dose of three to five minutes of moderate-to-vigorous activity per day was significantly related to better cognitive performance (36% lower risk of cognitive impairment)—an important message for older adults.
Zhu W, Wadley VG, Howard VJ, Hutto B, et al. Objectively measured physical activity and cognitive function in older adults. Medicine & Science in Sports & Exercise (2017); Vol. 49(1): 47–53.