Study finds link between increased risk of dementia and a sedentary life in front of the television | Science

Tracking hundreds of thousands of older people shows that those who watch more television are more likely to have dementia. However, the same is not true if they use the computer, a less passive mental behavior. This research, which highlights the benefits of physical activity, shows that being sedentary is not bad for the brain per se: it depends on what you do while sitting.

Science has accumulated enough tests that link mental health with physical activity, especially when cognitive decline looms with age. Similarly, lack of exercise promotes the onset of coronary heart disease. among the most sedentary. But the link between physical inactivity and dementia has not yet been definitively established. Now, one of the largest studies to date looks at this relationship.

Researchers from several universities in the United States compared the mental health status of 146,651 older people when they were on average 64.5 years old with their situation a decade later. During this period, 3,507 of them (about 2.5%) were diagnosed with dementia. The participants in the study, drawn from an imposing public health tool (the British database UK Biobank) completed a series of questionnaires to find out about their physical activity and the time they spent sitting, in front of the television or in front of the computer (outside working hours).

Sports and more

The results of the comparison, recently published in the scientific journal PNASshow that once the other variables are controlled (sex, previous illnesses, smoking, work, age, etc.), physical activity seems to be associated with a lower probability of developing any type of dementia. The result confirms previous studies which have a link between sport and mental health also in the elderly. In April, for example, a job with several thousand Americans showed how physical exercise was linked to a lower incidence of Alzheimer’s disease. But this research also mentioned performing demanding cognitive tasks as part of a diet for healthy brain aging.

The strength of this new study is that it reveals a consistent relationship between physical inactivity and mental health, but not just any physical inactivity. The questionnaires asked participants how many hours a day they spent in front of the television or in front of a computer screen. What they observed was that the more time you spend sitting in front of the television, the more likely you are to have dementia after a decade of follow-up. The increased risk percentage is up to 40%. But it is not the same with computers: the probability of developing dementia in this case drops to 20%.

“It’s possible that leisure computer use is cognitively demanding in a way that counteracts the risks of sitting too long”

David Raichlen, researcher at the University of Southern California

David Raichlen studies the impact of physical activity on human health and well-being at the University of Southern California and is the lead author of the study published in PNAS. Raichlen points out that it is no longer worth condemning a sedentary lifestyle without differentiating what one is doing, even if one is sitting. But he also acknowledges that it is not easy to know why the computer is better than television. “We know that cognitive demand can have benefits for the brain, and it’s possible that leisure computer use is cognitively demanding in a way that counteracts the risks of sitting too long,” he says. it in an email.

To confirm this, adds Raichlen, “both more detailed investigation of mechanisms and design of interventions to determine causal relationships” would be needed, since his study “can only really detect associations.” The relationship between a sedentary lifestyle and lower energy consumption and muscle metabolism is obvious, but it’s not so easy to know how it affects cognitive deterioration beyond the metaphor of muscle training. brain.

Neutralize the TV

A few weeks ago, neuroscientists from German Center for Neurodegenerative Diseases published the partial results of a work still in progress. They performed brain imaging on 2,500 people wearing an accelerometer to record their physical activity. They found that those who exercised more tended to have greater volume in critical areas such as the hippocampus, memory control button. Although the sample includes adults under the age of 65, the protective mantle of sport is more pronounced among those over 70.

The researchers in this study also investigated the relationship between physical activity and sedentary time (television or computer). They wanted to know if the first modulated or reduced the risk caused by the second. Taking as a reference the group of people with more physical activity and less time watching television, they observed a clear trend in which those who spent more hours watching television had a higher risk of dementia, regardless of the intensity of the physical exercise, although it decreased slightly in those who practiced intensive sport. “We find that physical activity reduces the risk of dementia, but it doesn’t completely neutralize the risks associated with watching TV,” Raichlen says.

According to data from the World Health Organization, Alzheimer’s disease and other dementias affect around 50 million people worldwide, or around 5% of the world’s elderly population. Everything indicates that the numbers will increase due to increased life expectancy and aging. The prevalence of the different types of dementia, almost testimonial among those under 60, increases with age and explodes among those who reach 85-90, a group half of whom suffer from mental disorders. Hence the urgency of determining whether or not there is a healthy sedentary lifestyle for the brain.

Different sedentary lifestyles

For neuropsychologist David Bartrés-Faz of the Guttmann Institute, Raichlen’s research published in PNAS seems very relevant. “This is one of the largest samples followed by 60-year-olds without dementia for 12 years”, specifies this expert in mental health and cognitive disorders. What matters most to him is the distinction between the different ways of being sedentary. “A sedentary lifestyle had been linked to cognitive deterioration and higher mortality, but now the relationship is not so clear,” he comments. However, what Bartrés-Faz appreciates most about the study is that the protective effect of physical exercise does not affect the risk of dementia from watching so much television. “If you spend hours in front of the television, the risk is not reduced if you go to the gym an hour later. It’s good to go to the gym, but you also have to stop watching television, ”recalls the principal researcher of the Barcelona Brain Health Initiative.

However, Bartrés-Faz sees some limitations to the research. The main one is that they did not carry out a baseline study of the cognitive state of each participant at the start of the survey. And this leads to the risk of reverse causation: “It is possible that those who watch more television have greater cognitive impairment or fewer abilities that lead them to choose a more passive activity, such as watching television”, underlines- he.

The researcher of the Institute of Biomedical Research of Barcelona (IIBB-CSIC) Coral Sanfeliu is also delighted that one type of sedentary lifestyle is beginning to differentiate itself from another and gives a good example: “Even if you are the other end of life, the school is sedentary”. And he agrees with the authors of the research: “Being in front of the computer is not the same as being in front of the television. Technological tools are already beginning to be taught in residences to combat cognitive deterioration”. Sanfeliu ends the comparison with school children: “Children who do more physical activity improve their school performance, their concentration or their maturation process. You need to combine both things, exercise and an active sedentary lifestyle.

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