There is growing evidence that physical activity has neuroprotective benefits. Countless studies have found that people who exercise regularly are more likely to maintain gray matter brain volume and white matter integrity across their lifespan. (See here, here, here, and here.) Additionally, staying physically active as we age may help to prevent the onset of and .

That said, the million-dollar question remains: What is the optimal “dose” (intensity × duration) of weekly physical activity required to promote healthy brain aging and reduce someone’s risk of dementia?

To answer this question, a team of researchers affiliated with Boston University School of Medicine (BUSM) and the Framingham Heart Study analyzed data from 2,354 community-based participants who agreed to have their total steps walked per day—along with the intensity and duration of daily walking (e. ., casual strolls vs. brisk walks)—monitored over a four-year period. Participants also agreed to undergo an MRI to measure total cerebral brain volume (TCBV).

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According to the authors, the objective of this study was “to assess the association of total steps walked per day and total dose (intensity × duration) of physical activity (PA) with brain volumes on magnetic resonance imaging (MRI) among Framingham Heart Study participants.”

After spending over three years combing through swaths of data, these findings were published today by JAMA Network Open in a paper “Association of Accelerometer-Measured Light-Intensity Physical Activity With Brain Volume.” The main takeaway of this research is that walking 10,000 or more steps per day was associated with higher total cerebral brain volumes in comparison to participants who walked fewer than 5,000 steps per day.

This research was led by Nicole Spartano, a research assistant professor of medicine at BUSM. In a statement, she said:

“Every additional hour of light-intensity physical activity was associated with higher brain volumes, even among individuals not meeting current Physical Activity Guidelines. These data are consistent with the notion that potential benefits of physical activity on brain aging may accrue at a lower, more achievable level of intensity or volume.”

The most recent Physical Activity Guidelines for Americans (Piercy et al., 2018) recommend that adults should strive for 150 minutes of moderate-to-vigorous physical activity (MVPA) per week (approximately 21.4 minutes per day) to optimize the health benefits of staying physically active. Unfortunately, this level of weekly MVPA is impossible for many people. Therefore, the guidelines emphasize that any “dose” of physical activity is better than none.

In the Discussion section of their paper, Spartano et al. write:

"Our observations support this new update to the guidelines, suggesting that incremental PA was associated with larger total brain volume at a relatively low-intensity threshold (as measured by light-intensity PA). However, our observation that MVPA was not significantly associated with brain volume after adjusting for light-intensity PA suggests that it is unclear whether individuals can expect further gain in benefit with higher-intensity activity."

What Doses of Physical Activity Provide What Benefits?

Based on the assumption that exercise is medicine, researchers are continuing to dial in on the benefits of various prescriptive doses of physical activity.

For example, the results of another four-year study (Dunlop et al., 2019) of 1,564 adults over age 49 on the benefits of walking were published early this month. This study found that 56 minutes of moderate-to-vigorous intensity walking per week was the baseline for staving off immobility in older adults. (See “8 Minutes of Walking Per Day Could Change Your Life.”)

As another example of the “dose-response” brain benefits of light-intensity physical activity, a study from last year (Suwabe et al., 2018) reported that a single 10-minute bout of mild exercise appeared to improve brain connectivity and enhance .

"We have really only just begun to uncover the relationship between physical activity and brain health,” Spartano said in a statement. She also emphasizes the importance of researchers exploring what the detrimental impact of physical inactivity and poor cardiovascular fitness (Spartano et al., 2016) has on total cerebral brain volume and healthy brain aging in community-based cohorts representing diverse racial, ethnic, and socio-economic groups. (See, "Can Being a Couch Potato Shrink Your Brain?")