White matter is brain tissue containing nerve fibers responsible for brain communication. As we age, nerve fiber activity declines and disrupts brain function. But a new study suggests that among older adults, the structural integrity of white matter is not only dependent on levels of physical activity, but also on the amount of remaining time spent sedentary.

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Adults who spent more time sedentary, even if they engaged in light or moderate-to-vigorous physical activity, had lower structural integrity in the white matter of the hippocampus, a region important for memory and learning.

Lead researcher Agnieszka Burzynska, a postdoctoral researcher at the University of Illinois, and her team publish their findings in the journal PLOS ONE.

Past studies have associated physical activity among older adults with reduced cognitive decline. In 2012, research from the University of Scotland in the UK found that seniors who had high levels of physical activity had fewer problems with memory and thinking skills, while a 2013 study claimed exercise is beneficial for the cognitive functioning of dementia patients.

The researchers say that such outcomes may be a result of improved structural activity within the white matter of the brain. "However," they add, "little is known about the associations of different levels of physical activity, sedentary behavior and cardiorespiratory fitness with the integrity of aging white matter."

Avoiding 'subjective' and 'imprecise' monitoring using accelerometers

With this in mind, Burzynska and her team monitored the physical activity levels of 88 participants aged 60-78 who were healthy but deemed "low-fit."

The researchers note that past research has required participants to self-report their exercise levels, but they say this is "subjective" and "imprecise." In this study, the team asked subjects to wear accelerometers on their hip for 7 consecutive days during all waking hours, except for when they were bathing or swimming.

This allowed the team to consistently monitor participants' engagement in physical activity, as well as their sedentary behavior, "so it's not what they say they do or what they think they do, but we have measured what they are actually doing," says Burzynska.

The participants also underwent brain imaging that showed the structural integrity of white matter and displayed the presence of any white matter lesions - areas of dead cells that form clumps. These lesions are common in seniors, occurring in around 95% of adults aged 65 and over. But the team notes that their early onset or fast accumulation can lead to brain dysfunction.

Sedentary behavior, despite physical activity, 'can be detrimental to the brain'

Results of the study revealed that participants who engaged in moderate-to-vigorous physical activity had fewer white matter lesions than those who engaged in low-level physical exercise.

Adults who frequently engaged in light physical activity, however, had greater structural activity in the white matter of the temporal lobes, which play an important part in memory, language, sight and hearing.

But perhaps most interesting was that adults who spent more time sedentary, even if they engaged in light or moderate-to-vigorous physical activity, had lower structural integrity in the white matter of the hippocampus, a region important for memory and learning.

Explaining what this finding means, Burzynska says:

"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. We hope that this will encourage people to take better care of their brains by being more active."

The team says their findings support health recommendations for adopting an active lifestyle in older age and pave the way for further research into the link between bodily fitness and white matter integrity.

Physical activity in seniors may not only have benefits for the brain. Medical News Today recently reported on a study claiming that for older women, exercise reduces the risk of arrhythmia - irregular heartbeat.