Changes in the brain were discovered in people who used to watch a lot of television decades ago

Their MRI scans showed that the areas of the brain involved in memory formation were smaller, and signs of damage to small blood vessels were more common in the white matter. Such changes are associated with brain ageing, a decline in cognitive ability and an increased risk of dementia.

However, the study does not prove that watching television shrinks the brain or causes Alzheimer’s disease. The researchers found a link between the habit and the MRI results, but did not establish the cause of this link.

Details

The researchers analysed data from approximately 1,700 participants in the US ARIC project, which focuses on heart, vascular and brain health.

The study began in 1987–1989. The average age of the participants at that time was 53. They were asked how often they watched television in their free time and how much of their working day they spent sitting down.

The responses were fairly general: ‘never or rarely’, ‘sometimes’, ‘often’ and ‘very often’. The researchers did not measure the exact number of hours spent in front of a screen.

More than two decades later, the participants underwent brain MRI scans. The researchers then compared the scans with the responses the participants had given in middle age.

Those who watched television frequently or very frequently were found to have a smaller volume in certain areas of the brain than those who hardly ever watched television.

The differences affected the hippocampus and the entorhinal cortex — areas essential for forming and retaining memories. These are among the first areas to be affected in Alzheimer’s disease.

Certain areas of the frontal and occipital lobes were also found to be smaller. The frontal lobes are involved in planning, decision-making and behavioural control, whilst the occipital lobes primarily process visual information.

In addition, TV enthusiasts had more areas of increased intensity in the white matter. On an MRI scan, these appear as bright spots and may indicate damage to the brain’s small blood vessels. Such changes become more common with age and are associated with an increased risk of stroke and cognitive impairment.

The association remained even after the researchers took into account physical activity, diabetes, body mass index, smoking and alcohol consumption.

It wasn’t just about sitting

The most unexpected finding came from comparing watching television with sedentary work.

Participants who spent a lot of their working time sitting did not show the same MRI findings. Moreover, certain areas of their brains were larger, and they showed fewer signs of white matter damage.

This does not mean that sedentary work protects the brain. Office workers may differ in terms of educational attainment, income, access to healthcare and the complexity of the tasks they perform. It is impossible to completely isolate the influence of these factors in an observational study.

The authors suggest that it is not just inactivity that matters, but also the nature of a person’s occupation. ‘Sedentary work’ often requires attention, planning, memorisation and communication. Watching television usually involves a more passive intake of information.

For now, this is merely a possible explanation. The researchers did not assess the content of the programmes, the degree of viewer engagement, or other activities the viewer might have been engaged in at the same time.

Nor can one conclude from the results that any kind of computer work is more beneficial than an evening TV drama. The study relates to television viewing habits in the late 1980s, rather than modern streaming services, social media, video games or smartphones.

Why men stood out more

When the data were broken down by gender, most of the links between television viewing and brain structure were found in men.

The reason is unknown. It could be due to biological differences, lifestyle factors or a statistical effect arising from dividing the sample into smaller groups.

The result does not imply that frequent television viewing is safe for women. Gender differences need to be confirmed in new studies specifically designed to make such a comparison.

What the study did not prove

Participants did not undergo brain MRI scans at the time of the first survey. Therefore, the researchers do not know whether brain volume changed over the subsequent decades or whether the differences existed from the outset.

A reverse causal relationship is also possible. For example, health status, cognitive ability, education or behavioural traits could have simultaneously influenced both television viewing habits and the results of the later MRI scans.

Furthermore, viewing frequency was assessed based on the participants’ own reports and categorised into just four broad categories. People may have recalled their habits inaccurately, or may have changed them completely over the course of 20 years.

Only a proportion of the participants in the long-term study reached the MRI stage. Those who agreed to the scan and lived long enough to undergo it may have been healthier than the rest. This, too, could have influenced the results.

Finally, a reduced volume in certain areas and lesions in the white matter do not constitute a diagnosis of dementia. The study did not reveal how many participants developed Alzheimer’s disease, nor whether time spent watching television was the cause of the condition.

Why this matters

Studies of sedentary lifestyles usually focus on the number of hours spent inactive. This new research suggests that grouping all sedentary activities into a single category may be misleading.

Reading, board games, conversation, intellectual work and passive television viewing may place entirely different demands on the brain, even though the person remains seated in all these cases.

If the findings are confirmed, recommendations for healthy ageing may take into account not only the duration of sitting but also the nature of the activity. However, the current study does not yet allow us to establish a safe limit for watching television or to promise that swapping a TV series for a puzzle will prevent dementia.

For the average viewer, the conclusion does not mean that a single evening in front of the screen is dangerous. The study concerns a long-standing habit established in middle age and shows a statistical correlation at the group level, rather than the fate of any individual.

Background

The brain’s white and grey matter gradually change with age. A reduction in the volume of the hippocampus and entorhinal cortex may be accompanied by a decline in memory, whilst damage to small blood vessels affects the condition of the white matter.

Physical activity is considered one of the factors associated with healthier brain ageing. However, a lack of physical activity is only one possible consequence of prolonged television viewing. Eating whilst watching television, sleep disturbances, social isolation and a lack of mental stimulation may also play a role.

Previous studies have already identified similar links. For example, in the US-based CARDIA study, frequent television viewing over a 20-year period was associated with a lower volume of grey matter in middle age. However, that study was also observational and did not establish causality.⁠

The new study broadens the picture: it examines more areas of the brain, the condition of white matter, and the differences between watching television and sitting at work.

Source

A study by Nathan Feter, Anamika Nanda, Sarah Khurihan, David Reichlen and their colleagues, *Associations of distinct sedentary behaviours with cortical, subcortical, and white matter hyperintensity volumes: Evidence from the ARIC study*, was published in the journal *Alzheimer’s & Dementia* in 2026.