26 Apr 2019

Current health guidelines encourage people to hit the gym or go for a jog several times per week, but a new study suggests that engaging in much lighter forms of physical activity could bestow benefits upon the brain. In a paper published April 19 in JAMA Network Open, researchers led by Nicole Spartano at Boston University reported that low-intensity movement—such as leisurely walking, gardening, or even doing household chores—correlated with larger total brain volumes in people over age 50. Moderate to vigorous exercise, such as jogging or aerobics, did not correlate further with brain volume after the researchers controlled for light activity.

Cross-sectional study correlated physical activity with brain volume.

Every hour of light physical activity per day, on average, correlated with a 0.35 percent bigger brain.

After correcting for light exercise, moderate to vigorous exercise did not associate with brain volume.

Shannon Halloway of Rush University Medical Center in Chicago said that the findings have important public health implications, especially since people tend to let go of structured exercise as they age. “Yet, if lifestyle physical activities that are of light intensity are maintained or increased with age, there may still be benefits to the brain,” she added. Halloway recently came to similar conclusions in a smaller cohort (Halloway et al., 2018).

Current U.S. public health guidelines suggest adults get at least 150 minutes of moderate to vigorous physical activity per week, or just over 20 minutes per day. However, only a quarter of adults over age 60 do so (Tucker et al., 2011). Many studies suggest that regular exercise improves overall health and curbs dementia risk, but few have investigated the effects of mild physical activity, which includes any type of movement easier than a brisk walk (Blondell et al., 2014; Tan et al., 2016; Mar 2018 news). This level of movement was difficult to track because people are bad at accurately gauging how much time they spend simply pottering about. With the advent of accelerometers, investigators can now objectively measure this background bustling.

That’s what Spartano and colleagues did. They wondered whether time spent in motion each day might correlate with a brain benefit. They asked participants in the Framingham Heart Study, and 2,534 cognitively normal volunteers, who averaged 53 years old and ranged from the 40s to the 80s, strapped accelerometers around their waists for eight days. The devices counted steps and logged body movement counts, which were categorized into light, moderate, or vigorous physical activity based on their frequency. The volunteers had brain MRIs to measure gray- and white-matter volume. The researchers chose these measures because brain volume shrinks with age, and faster shrinkage correlates with neurodegenerative disease (for review see Pini et al., 2016).

Based on accelerometer recordings, nearly half the participants met the guidelines of 150 minutes/week of moderate to vigorous physical activity. They had lower rates of hypertension, diabetes, and cardiovascular disease than those who did not, but there was no significant difference in brain volume between the two groups. However, the number of steps taken per day, and time spent engaged in light intensity activity, did associate with brain volume. Participants spent an average of nearly 2.5 hours per day moving in light ways.

People who walked at least 10,000 steps per day had, on average, 0.35 percent larger total cerebral brain volume than those who took less than 5,000 steps. Based on a study that reported a 0.2 percent loss of brain volume per year after age 60, this 0.35 percent translates into a brain that is 1.75 years younger, at least in terms of size, noted the authors (Debette et al., 2011). Calculated another way, each additional hour spent in motion per day, at least as determined over this brief eight-day period, associated with one year less of brain aging in this population. These associations between brain volume and light exercise were stronger in people who did not meet the guideline of 150 minutes per week of mild to vigorous activity. They did not hold in people younger than 50.

What about more intense exercise? Spartano reported that while people who engaged in 10–19 minutes of moderate to vigorous exercise per day had a higher brain volume than those who pushed it for less than 10 minutes, that association disappeared when the researchers adjusted their statistical model for light-intensity activity. Spartano said it is difficult to distinguish the effect of structured, vigorous exercise from a merely active lifestyle, because most people who made a concerted effort to work out also tended to be more active overall. She said that larger, longitudinal studies are needed for that. Engaging in more intense exercise was not entirely without benefit in this study, however, as it associated with larger white-matter volumes.

Did people work out more simply because they were being monitored? Spartano acknowledged this was highly likely. However, she pointed out that since only about half of the people in the older age groups got more than five minutes of moderate to vigorous exercise per day, monitoring probably did not motivate those people that much. While a longer monitoring period might have captured more routine exercise patterns, Spartano thought the additional burden might temper enrollment.

“This study nicely shows the positive association of physical activity and brain volume in age groups from 50 years and older, when the atrophic changes start to appear,” commented Hilkka Soininen of the University of Eastern Finland in Kuopio. “From a public health perspective, these kind of studies are important when health promoting advice and programs are formulated for the aging populations,” she added.—Jessica Shugart