Debating the Direction of Causation Between Physical Decline and Cognitive Decline in Aging

Researchers here suggest that the direction of causation between physical decline and cognitive decline is largely the opposite of the present consensus. Most of the evidence of recent decades points to physical decline, and associated lack of activity, having a negative impact the brain. Certainly there are any number of studies showing exercise to have a beneficial effect on cognitive function. Here, however, researchers propose that declines in cognitive function lead the declines in physical function in aging.

Someone dies somewhere in the world every 10 seconds owing to physical inactivity - 3.2 million people a year. From the age of 50, there is a gradual decline not just in physical activity but also in cognitive abilities since the two are correlated. But which of them influences the other? Does physical activity impact on the brain or is it the other way around?

"Correlations have been established between these two factors, particularly in terms of memory, but also regarding the growth and survival of new neurons. But we have never yet formally tested which comes first: does physical activity prevent a decline in cognitive skills or vice versa? That's what we wanted to verify. Earlier studies based on the correlation between physical activity and cognitive skills postulated that the former prevent the decline of the latter. But what if this research only told half the story? That's what recent studies suggest, since they demonstrate that our brain is involved when it comes to engaging in physical activity."

Researchers tested the two possible options formally using data from the SHARE survey (Survey of Health, Aging and Retirement in Europe), a European-wide socio-economic database covering over 25 countries. The cognitive abilities and level of physical activity of 105,206 adults aged 50 to 90 were tested every two years over a 12-year period. Researchers employed this data in three separate statistical models. In the first, they looked at whether physical activity predicted the change in cognitive skills over time; in the second, whether cognitive skills predicted the change in physical activity; and in the third, they tested the two possibilities bidirectionally.

The researchers found that the second model adjusted the most precisely to the data of the participants. The study demonstrates, therefore, that cognitive capacities mainly influence physical activity and not vice versa, as the literature to date had postulated. "Obviously, it's a virtuous cycle, since physical activity also influences our cognitive capacities. But, in light of these new findings, it does so to a lesser extent."

Link: https://www.unige.ch/communication/communiques/en/2020/muscles-et-cerveau-qui-entraine-qui/

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