Frequent consumption of television content is associated with an increase in the volume of hyperintense white matter, which is detected on magnetic resonance imaging. This increase indicates processes of demyelination and axonal loss caused by impaired microcirculation. Furthermore, individuals who regularly watch television showed a decrease in the volume of certain cortical areas of the cerebral hemispheres.
Comparison with other risk factors
It is important to note that a sedentary lifestyle accompanied by mental activity, such as working on a computer, did not cause similar negative changes. The results of this study were published in Alzheimer’s & Dementia.
Study methodology
There are many studies linking physical activity to maintaining brain structure in areas related to dementia. Conversely, accumulated data suggest that a sedentary lifestyle may increase the probability of developing dementia, but the impact of such a lifestyle on changes in brain structure remains insufficiently studied. Attention is also lacking regarding how a sedentary lifestyle can manifest in different behavioral scenarios, each having its own cognitive and physiological impact.
The research team, led by Nathan Fetter from the University of Southern California, studied the relationship between different forms of sedentary behavior and changes in brain structures in 1712 healthy individuals whose age ranged from middle-aged to elderly (the average age of the group was 53 years). Participants self-assessed their frequency of watching television and time spent sitting at work using the Beck Physical Activity Questionnaire. Time spent in front of the television was classified into five categories: 'Never', 'Rarely', 'Sometimes', 'Often', and 'Very often'. Sitting at work was determined by selecting one option for the statement 'At work you sit...': 'Do not work', 'Never', 'Rarely', 'Sometimes', 'Often', or 'Always.'
Key scientific findings
Upon final data collection, the average age of participants reached 76 years, and the average observation period was 23.7 years. Scientists established a context-dependent relationship between sedentary lifestyle and changes in several brain areas. Of particular interest was very frequent television viewing, which correlated with a decrease in the volume of specific areas.
The opposite pattern was observed in participants who reported always sitting while working, including computer work; they demonstrated a significant increase in volume. Additional analysis showed that watching television was associated with a decrease in volume in various areas of both hemispheres (p ≤ 0.047), whereas prolonged sitting at the workplace led to an increase in these areas (p ≤ 0.049).
When segmenting the data by sex, it was found that frequent television viewing increased the volume of hyperintense white matter in both sexes. Among men, a more pronounced decrease in the volume of the cortex and subcortex in areas responsible for emotional processing and cognitive functions was identified.
Researchers' conclusion
The researchers believe that separating the contexts of sedentary behavior in this study highlights the complexity of comprehensively assessing the influence of this parameter on the central nervous system. They concluded that active mental activity while sitting at work protects brain structures from damage, whereas passive mental stimulation, such as watching television, has a negative effect on them. The data obtained may serve as a foundation for developing dementia prevention programs for older adults.