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Being lazy in middle age has been linked with having a smaller brain in later life. Scientists looked at the brains and fitness levels of more than 1,000 people when they were 40, and then again 20 years later.
The findings, published in the journal Neurology, showed that those with poorer fitness levels – carried out through a treadmill test – in middle age generally had a smaller brain volumes two decades later, and that the amount the brain had shrunk correlated with how unfit the person was.
The team, from the Boston University School of Medicine is the US, established how fit a person was by looking at how much oxygen the body was capable of using in one minute. This is also known as 'peak VO2'. They estimated the VO2 by looking at the length of time participants were able to exercise on the treadmill before their heart rate reached a given level.
Findings showed that for every eight units lower a participant performed on the exercise test, their brain volume was smaller 20 years later, equivalent to two years of accelerated brain ageing. Researchers said their study was the first to demonstrate that early mid-life cardiovascular fitness is associated with reduced brain volume in later life.
"Evidence suggests that exercise, which improves fitness levels, influences signalling pathways and the neuroplasticity of the brain, reducing brain atrophy and cognitive decline with age," they wrote, adding that although not studied on a large scale, the findings could indicate that mid-life exercise could prevent cognitive decline in older age. "Promotion of mid-life cardiovascular fitness may be an important step towards ensuring healthy brain ageing in the population."
Study author Nicole Spartano said that the findings are observational and it does not prove that poor fitness causes brain-volume loss – but it does show an association. They also say that there are a number of limitations to the study. "Our findings warrant confirmation in future investigations," they concluded.
"We did not account for multiple statistical testing; further, the largely homogeneous racial profile [white individuals of European ancestry] ... decreases the generalisability of our findings to other racial and ethnic groups. Finally brain MRI measures were only available in later life, thereby hampering our ability to evaluate changes over time."