Too much TV time could mean a higher risk of dementia

Other, less passive sedentary behaviors, such as using the computer, are instead associated with better mental health

Television screen
A man looks at a television screen at home.SANTI BURGOS

According to a study that tracked more than 100,000 older people, those who watch more television are more likely to develop dementia. However, this is not the case for seniors who use a 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 in of itself: it all depends on what you are doing.

Science has found a lot of evidence linking good mental health with physical activity, especially in the case of age-related cognitive impairment. Similarly, lack of exercise is linked to coronary diseases among the most sedentary people. But the connection between a sedentary lifestyle and dementia has not yet been categorically established. Now, one of the largest studies to date takes a look at this connection.

Researchers from several US universities compared the mental health status of 146,651 elderly people when they had an average age of 64.5, with their situation a decade later. In that time, 3,507 of them (about 2.5%) were diagnosed with dementia. The participants of the study, obtained from an impressive public health tool (the British database UK Biobank) filled a series of questionnaires to determine their level of physical activity and the time they spent sitting, either watching television or in front of the computer (excluding working hours).

Exercise and the elderly

The results of the comparison, recently published in the scientific journal PNAS (Proceedings of the National Academy of Sciences of the United States of America), show that once other variables are controlled (sex, previous illnesses, smoking, work, age and more), physical activity appears to be related to a lower chance of developing any type of dementia. The result confirms previous studies that have also linked sports and mental health in the elderly. In April, for example, a study carried out with several thousand Americans showed how physical exercise was related to a lower incidence of Alzheimer’s. However, that study also included performing demanding cognitive tasks as part of the formula for good brain aging.

The highlight of this new study is that it reveals a consistent relationship between a sedentary lifestyle and mental health – but not just any sedentary lifestyle. The questionnaires asked participants how many hours a day they spent either watching television or in front of a computer screen. What they noticed is that the longer the participants spend sitting in front of the TV, the more likely they were to have dementia a decade later; the risk increased up to 40%. That is not the case of computers, where the likelihood of developing dementia drops up to 20%.

David Raichlen researches 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. Raichlen argues that we should condemn a sedentary lifestyle without distinguishing what the person is doing, even if they are sitting. But he also acknowledges that it is difficult to know why the computer is better than television. In an email, he explained that cognitive demand could have benefits for the brain, and that using the computer during leisure time could be cognitively demanding in a way that counteracts the risks of sitting for too long.

To confirm this, he adds, a more detailed investigation of the mechanisms would be needed. Interventions would also need to be designed to determine causal relationships, because their study can only detect associations. The link between a sedentary lifestyle and lower energy consumption and muscle metabolism is evident, but it is not so easy to know how it affects cognitive deterioration beyond the metaphor of training the brain.

Neutralizing the TV

A few weeks ago, neuroscientists from the German Center for Neurodegenerative Diseases published the partial results of a work in progress. They performed brain imaging on 2,500 people who wore an accelerometer to record their physical activity. They found that those who performed more physical exercise tended to have a larger volume in critical areas like the hippocampus, the control center of memory. Although the sample included adults under 65 years of age, the benefit of exercise was more noticeable in those over 70 years of age.

The researchers of the current study also looked into the relationship between physical activity and sedentary lifestyle (either television or computer). They wanted to know if the former modulated or reduced the risk caused by the latter. Taking as a reference the group of people with more physical activity and less TV time, they noticed a clear pattern in which those who spent more hours watching television had a higher risk of dementia, regardless of the intensity of physical exercise, although it decreased slightly in those who actively performed sports.

According to data from the World Health Organization, Alzheimer’s and other types of dementia affect close to 50 million people worldwide, about 5% of the world’s elderly population, and everything suggests that those numbers will grow due to the rise in life expectancy. The prevalence of the different types of dementia increases with age and peaks among those who reach 85-90 years, a group in which half have mental problems; hence the urgency in determining how a sedentary lifestyle affects the brain.

Different sedentary lifestyles

For neuropsychologist David Bartrés-Faz, lecturer at the University of Barcelona and associate researcher at the Guttmann Institute, Raichlen’s research is very important. “This is one of the largest samples following 60-year-olds with no dementia for 12 years,” says the expert in mental health and cognitive decline. What is most important to him is the distinction between the different ways of being sedentary. “A sedentary lifestyle had been related to cognitive deterioration and higher mortality, but currently the relationship is not so clear,” he says. However, what Bartrés-Faz most values about the study is how the protective effect of physical exercise does not affect the risk of dementia from watching too much television. “If you spend hours in front of the television, the risk will not decrease even if you go to the gym for an hour afterwards. Going to the gym is okay, but you should also cut down on TV,” points out the lead investigator of the Barcelona Brain Health Initiative.

However, Bartrés-Faz sees a few limitations regarding the research. The main one is that they did not carry out a baseline study of the cognitive status of each participant at the beginning of the investigation. This brings a risk of reverse causality: “There is a possibility that those who watch more television had a greater cognitive impairment or fewer abilities, which led them to choose a more passive activity, like watching TV,” he says.

Coral Sanfeliu, a researcher at the Barcelona Institute for Biomedical Research (IIBB-CSIC) is also pleased that one type of sedentary lifestyle is beginning to be differentiated from another, and mentions a great example: “Even if you are at the other side of life, school is sedentary.” She 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 nursing homes to fight cognitive deterioration.” Sanfeliu continues the comparison with schoolchildren: “Children who do more physical activity improve their school performance, their concentration or their maturation process. You have to combine both things – exercise and an active sedentary lifestyle.”

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