Lots of sitting ‘affects memory’

If you want to take a good stroll down memory lane, new research suggests that you’d better get out of your chair more often.

In a first-of-its-kind study, researchers have found that in people middle-aged and older, a brain structure that is key to learning and memory is plumpest in those who spend the most time standing up and moving.

At every age, prolonged sitters show less thickness in the medial temporal lobe and the subregions that make it up, the study found.

The prospect of thinning in the medial temporal lobe should spark plenty of worry. Some loss of volume there occurs naturally as we age, and the result is poorer episodic memory – the kind that brings to mind events from one’s past.

But shrinkage of the brain and its memory centres becomes particularly pronounced in dementia, and thinning of the cortex probably contributes to that. Even before Alzheimer’s disease steals memories, the condition begins to change the density and volume of the hippocampus and the entorhinal cortex, memory-making structures that lie at the heart of the medial temporal lobe.

The study’s findings are based on interviews and tests of 35 cognitively healthy people between the ages of 45 and 75. Researchers at UCLA’s Semel Institute and its Centre for Cognitive Neurosciences asked them about their physical activity patterns, and scanned their brains. Then they gauged how self-reported sitting time or physical activity levels corresponded to thickness in these critical brain structures.

The subjects reported average sitting times of three to 15 hours a day. After adjusting for the subjects’ ages, the researchers found that every additional hour of average daily sitting was associated with a 2 per cent decrease in the thickness of the medial temporal lobe.

The research suggests that, compared to a person who sits for 10 hours a day, someone of the same age who typically sits for 15 hours would have a medial temporal lobe that is 10 per cent thinner. And this, says study leader Prabha Siddarth, represents a lot of missing brain.

The study did not find any correlation between subjects’ exercise habits and the thickness of either their medial temporal lobe or its constituent structures. This surprised the researchers, since other studies have found that brain volume is generally greater – and cognitive performance is better – in people who work out more.

Siddarth cautioned that for inveterate sitters, even regular bouts of intensive exercise would not undo the damage.

‘‘If you’re sitting for long periods of time, it seems that that factor – not physical activity – becomes the more harmful or more significant measure of your fitness. Even for people who are physically active, sitting a lot seems to be bad for your brain.’’

This was consistent with studies of sitting’s effects on such health measures as heart disease, diabetes and mortality, she said.