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 The human brain typically shrinks as people age, with volume
declining by about 0.2 percent per year by age 60 and with excessive
shrinkage linked with cognitive problems, Nicole Spartano of Boston
University School of Medicine and colleagues explain in JAMA Network
Open.
Their new research, done in middle aged adults, found that each
additional hour spent in light physical activity was associated with
0.22 percent higher brain volume. And spending 10 to 19 minutes per
day in moderate-intensity physical activity, like brisk walking, was
linked with 0.29 percent higher brain volume, compared to averaging
less than 10 minutes per day.
Those activity levels are lower than what guidelines suggest is
necessary to achieve substantial health benefits. Guidelines
typically say adults should aim for at least 150 minutes per week of
moderate-intensity physical activity (about 21 minutes per day), or
75 minutes per week of vigorous exercise, and at least 10,000 steps
per day.
In the new study, individuals who took at least 7,500 steps per day
had larger brain volumes than those averaging fewer than 7,500 steps
per day.
The researchers estimate that each additional hour of
light-intensity physical activity was associated with approximately
1.1 years less brain aging - although they caution that because
participants were relatively young, this estimate might not be
accurate.
They also note that the link between activity levels, step counts
and brain volume was not consistent, with a smaller benefit seen at
the highest levels of exertion.
For the study, the researchers had 2,354 middle-aged volunteers wear
a small accelerometer for at least three days (and up to eight
days), to measure their energy expenditure and step counts. The
researchers also used magnetic resonance imaging to assess
participants' brain volume in relation to their skull volume.
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"There shouldn't be very much extra space in the skull that is not
filled by brain tissue. If we see lots of extra space than this
suggests that the brain may have atrophied or shrunk and is linked
to dementia," Spartano told Reuters Health by email.
The finding that the lowest levels of physical activity were linked
with smaller brain volume even in middle age suggests that "some
adults may enter older age with lower brain volumes, putting them at
a disadvantage for maintaining this already depleted tissue," she
and her colleagues write in their report.
Yaakov Stern, a professor of neuropsychology at the Columbia
University Medical Center in New York City who was not involved in
the research, pointed out to Reuters Health that the study only
looked at brain volume and not whether different amounts of physical
activity translate into real-life benefits in cognitive function or
reduced risk of dementia.
Furthermore, observational studies like this one can't prove cause
and effect.
"Follow up trials where people are randomized to specific conditions
consisting of different intensities of exercise can help explore
more definitively what degree of physical activity is required for
increased brain health," Stern said in an email.
SOURCE: https://bit.ly/2XD0xdz JAMA Network Open, online April 19,
2019.
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