Dementia: What you do while you sit may affect your risk of brain decline, warns study

Phil Thompson discusses his fears of dementia

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Previous research has shown that a lack of exercise could put an older adult’s risk of dementia on par with that of an adult who is genetically predisposed to the condition. This is because sedentary behaviour can negate the protective effects of healthy genes. Now new findings suggest it’s not how long you’re inactive that matters, but what you do while sitting that affects your risk.

The new findings, published in the journal Proceedings of the National Academy of Sciences, found adults who indulge in passive behaviours while sitting may be at increased risk of dementia.

The research, conducted by USC and University of Arizona researchers, found adults aged over 60 to be at particularly high risk when they sat for prolonged periods.

Interestingly, the researchers found that the link between sedentary behaviour and dementia persisted among individuals who were physically active.

David Raichlen, professor of biological sciences and anthropology at the USC Dornsife College of Letters, Arts and Sciences, highlighted the importance of the activities performed during leisure time.

He said: “It isn’t the time spent sitting per se, but the type of sedentary activity performed during leisure time that impacts dementia risk.

“We know from past studies that watching TV involves low levels of muscle activity and energy use compared with using a computer or reading.

“And while research has shown that uninterrupted sitting for long periods is linked with reduced blood flow in the brain, the relatively greater intellectual stimulation that occurs during computer use may counteract the negative effects of sitting.”

Using self-reported data from the U.K. Biobank of more than 500,000 participants, researchers explored possible correlations between sedentary leisure activity and dementia.

They identified 145,000 participants who were dementia-free at the outset of the study who were asked to provide information about their sedentary behaviour during the period 2006 to 2010.

During the follow-up period of 12 years, the scientists discovered 3,507 positive cases of dementia through medical records.

After adjusting for other lifestyle characteristics that could affect brain health, researchers found an association between time spent watching TV and dementia risk.

They also found that leisure time spent using a computer was associated with a reduced risk of developing dementia.

Study author Gene Alexander, professor of psychology at the Evelyn F. McKnight Brain Institute at the University of Arizona, said the results challenge the assumption that physical activity counters the effects of sedentary behaviour.

He said: “Although we know that physical activity is good for our brain health, many of us think that if we are more physically active during the day, we can counter the negative effects of time spent sitting.

“Our findings suggest that the brain impacts of sitting during our leisure activities are really separate from how physically active we are […].

“Being more mentally active, like when using computers, may be a key way to help counter the increased risk of dementia related to more passive sedentary behaviours like watching TV.”

One major downside of physical inactivity is reduced cerebral blood flow to the regions of the brain key to memory.

Prolonged sedentary behaviour may also impair glucose and lipid metabolism, which are recognised as risk factors for cognitive decline.

Keeping the brain active, however, may help build reserves of healthy brain cells and connections between them.

This explains why people who have mentally stimulating jobs tend to have a significantly lower risk of dementia later in life.

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