Is There a Correlation Between Television Time and Dementia?

Sedentary behaviors, described as those that do not increase energy expenditure, are classified as activities spent sitting or lying down during waking hours⁽¹⁾.

Sedentary time is associated with the risk of multiple adverse outcomes such as coronary heart disease, stroke, obesity, metabolic syndrome, hypertension⁽²⁾.

In the U.S., sedentary behaviors are quite prevalent as indicated by approximately 68% of adults spend at least 2 hours or more watching television per day⁽³⁾.

Is television actually bad for your brain? 

We know that physical activity decreases your risk of cognitive impairment and dementia.

Not surprisingly, if more time is spent sitting and watching television, your risk of cognitive impairment and dementia will be higher than someone who does not spend as much time being sedentary.

What if you are getting regular exercise? Does watching television still pose risks for cognitive decline?

The first study that investigated this was published in 2005 and indicates that television is still bad for your brain despite getting regular exercise⁽⁴⁾.  

While most studies of aging and television viewing prior to this focused on the current viewing habits of elders over the age of 65; this research focused on middle-adulthood television viewing as an indicator of potential disease development in later life.

These researchers primary finding was that increased television viewing related to an increased possibility of having Alzheimer’s disease in their case-control study.

Television viewing is crucial because it affects the relative time spent on potentially beneficial activities such as intellectual or social endeavors, and may be a substitute for other unhealthy behaviors.

Time spent on watching television may potentially reflect a desire to avoid more stimulating activities and may be indicative of a mentally inactive lifestyle which has been shown to be associated with increased risk of cognitive decline with age.

Television viewing and cognitive decline

In 2018, the UK Biobank study started following approximately 500,000 individuals in the United Kingdom who were 37 to 73 years old⁽⁵⁾.

Researchers examined baseline participant performance on several different cognitive tests as described below:

• - Prospective memory (remembering to do an errand on your way home)
• - Visual-spatial memory (remembering a route that you took)
• - Fluid intelligence (important for problem solving)
• - Short-term numeric memory (keeping track of numbers in your head)

Five years later, many of these individuals repeated certain tests. Results of this study were clear. At baseline, there was a link between more television viewing and worse cognitive function across all the cognitive tests⁽⁵⁾.

1. Importantly, television viewing time was also linked with a decrement in cognitive function five years later for all the cognitive tests. Although this study cannot prove television viewing caused the decline in cognitive function, it is highly suggestive⁽⁵⁾.  
2. Interestingly, the type of sedentary activity mattered. Worse cognitive function was associated with both driving and television. Computer use was associated with better cognitive function at baseline, and a lower likelihood of cognitive decrements over the five-year study.

Isolating television viewing as the main indicator of cognitive decline

Sedentary behavior is also associated with cognitive and structural brain aging⁽⁶⁾. Characteristic sedentary behavior domains may potentially affect cognitive function differently.

Cognitively passive sedentary behaviors like watching television indicate negative associations with cognition, whereas cognitively active sedentary behaviors like computer use or reading demonstrate positive associations with cognitive function⁽⁷⁾.

There are no prospective studies investigating the association between different sedentary behavior domains and incident dementia.

In addition, no research has examined these relationships in relation to physical activity engagement. A recent study investigated if different leisure-time sedentary behavior domains (television watching vs. computer use) are associated with incident dementia and that these associations are not modified by engagement in physical activity⁽⁸⁾.

Main findings

It was demonstrated that sedentary behavior is associated with incident dementia, however the type of sedentary behavior determines the direction of the associations.

Essentially, time spent watching television is associated with increased risk of all-cause dementia, while leisure-time spent using a computer is associated with reduced risk of incident dementia.

The significance of these results was sustained following adjustment for demographic, health, and lifestyle variables, including time spent in physical activity and sleep, as well as in sensitivity analyses⁽⁸⁾.

These changes in risk were not minor.

In fact, those who watched the most television daily — more than four hours — were 24% more likely to develop dementia. Those who used computers interactively (not passively streaming) more than one hour daily as a leisure activity were 15% less likely to develop dementia.

Summary & Recommendations

Watching television is associated with increased risk of developing all-cause dementia, while computer use is associated with reduced risk of developing dementia.

Unlike other health outcomes, associations between sedentary behaviors and dementia are not strongly diminished with high levels of physical activity.

The overall objective for people is to focus on reducing leisure time spent in cognitively passive behaviors (i.e., television watching) and increase time spent in more cognitively active sedentary behaviors (i.e., computer, crossword puzzles, etc.)

These cognitively stimulating activities create promising targets for reducing risk of neurodegenerative disease regardless of levels of physical activity engagement.

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References:
1.    Matthews, C.E., et al., Amount of time spent in sedentary behaviors in the United States, 2003-2004. Am J Epidemiol, 2008. 167(7): p. 875-81.
2.    Healy, G.N., et al., Television time and continuous metabolic risk in physically active adults. Med Sci Sports Exerc, 2008. 40(4): p. 639-45.
3.    Juan W, B.P. Routine active and sedentary behavior patterns in U.S. adults: Nutrition Insight 40. 2008  [cited 2012; Available from: http://www.cnpp.usda.gov/Publications/NutritionInsights/Insight40.pdf.
4.    Lindstrom, H.A., et al., The relationships between television viewing in midlife and the development of Alzheimer's disease in a case-control study. Brain Cogn, 2005. 58(2): p. 157-65.
5.    Sudlow, C., et al., UK biobank: an open access resource for identifying the causes of a wide range of complex diseases of middle and old age. PLoS Med, 2015. 12(3): p. e1001779.
6.    Bakrania, K., et al., Associations Between Sedentary Behaviors and Cognitive Function: Cross-Sectional and Prospective Findings From the UK Biobank. Am J Epidemiol, 2018. 187(3): p. 441-454.
7.    Copeland, J.L., et al., Sedentary time in older adults: a critical review of measurement, associations with health, and interventions. Br J Sports Med, 2017. 51(21): p. 1539.
8.    Raichlen, D.A., et al., Leisure-time sedentary behaviors are differentially associated with all-cause dementia regardless of engagement in physical activity. Proc Natl Acad Sci U S A, 2022. 119(35): p. e2206931119.