Like everything else in the body, the white-matter fibers that allow
communication between brain regions also decline with age. In a new study, researchers found a
strong association between the structural integrity of these white-matter
tracts and an older person's level of daily activity – not just the degree to
which the person engaged in moderate or vigorous exercise, but also whether he
or she was sedentary the rest of the time.
The study, reported in the journal PLOS ONE, tracked physical
activity in 88 healthy but "low-fit" participants aged 60 to 78. The
participants agreed to wear accelerometers during most of their waking hours
over the course of a week, and also submitted to brain imaging.
"To our knowledge, this is the first study of its kind that uses
an objective measure of physical activity along with multiple measures of brain
structure," said University of Illinois postdoctoral researcher Agnieszka
Burzynska, who conducted the research with U. of I. Beckman Institute director Arthur Kramer
and kinesiology and community health
professor Edward McAuley.
Most studies ask subjects to describe how much physical activity they
get, which is subjective and imprecise, Burzynska said. The accelerometer
continuously tracks a person's movement, "so it's not what they say they
do or what they think they do, but we have measured what they are actually
doing," she said.
The researchers assumed that participants' activity levels over a week
accurately reflected their overall engagement, or lack of engagement, in
physical activity.
The study also relied on two types of brain imaging. The first,
diffusion tensor imaging, offers insight into the structural integrity of a
tissue by revealing how water is diffused in the tissue. The second method
looks for age-related changes in white matter, called lesions. Roughly 95
percent of adults aged 65 and older have such lesions, Burzynska said. While
they are a normal part of aging, their early onset or rapid accumulation may
spell trouble, she said.
The team found that the brains of older adults who regularly engaged
in moderate-to-vigorous exercise generally "showed less of the
white-matter lesions," Burzynska said.
The association between physical activity and white-matter structural
integrity was region-specific, the researchers reported. Older adults who
engaged more often in light physical activity had greater structural integrity
in the white-matter tracts of the temporal lobes, which lie behind the ears and
play a key role in memory, language, and the processing of visual and auditory
information.
In contrast, those who spent more time sitting had lower structural
integrity in the white-matter tracts connecting the hippocampus, "a
structure crucial for learning and memory," Burzynska said.
"This relationship between the integrity of tracts connecting the
hippocampus and sedentariness is significant even when we control for age,
gender and aerobic fitness," she said. "It suggests that the
physiological effect of sitting too much, even if you still exercise at the end
of the day for half an hour, will have a detrimental effect on your
brain."
The findings suggest that engaging in physical activity and avoiding a
sedentary lifestyle are both important for brain health in older age, Burzynska
said.
"We
hope that this will encourage people to take better care of their brains by
being more active," she said.
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