Watching TV might slow your brain

Sitting for prolonged periods of time and not being physically active is known to have a negative impact on health. For the first time, its effect on cognitive performance in young adults has also been investigated.

Watching extended amounts of TV might be linked to cognitive decline.

New research published in JAMA Psychiatry followed individuals for 25 years, charting their TV-watching schedule and exercise regimen.

Scientists looking at long-term health have long been worried about the ramifications of an increasingly sedentary lifestyle and the rise of screen-based activities.

The health implications of a sedentary lifestyle are known to include a higher risk of cardiovascular disease, certain types of cancer, type 2 diabetes and obesity.

Physically active people, on the other hand, are likely to live longer and are less inclined to suffer from depression.

There is also a steadily growing body of evidence that physical activity helps improve, or maintain, cognitive function. The current study by a team of researchers at the Northern California Institute for Research and Education at the Veterans Affairs Medical Center, takes a deeper look.

Links between cognitive function and exercise

Very few studies have investigated the links, if any, between physical activity in early adulthood and cognitive function later in life.

Results from a British study, published in 2003, examined the relationship between physical activity in adults during their mid-30s and their consequent cognitive health in later life. The study found that physical exercise at 36 years of age was associated with a significantly slower rate of decline in memory between the ages of 43 and 53.

Other studies that investigated younger individuals used retrospective data, which is not optimal. The current study is the first of its kind to look at sedentary behavior, TV watching, exercise and its long-term cognitive effects on young adults (aged 18-30).

The study used data from 3,247 adults (split roughly evenly between males and females, white and black). The participants, from five US cities, were taken from the Coronary Artery Risk Development in Young Adults (CARDIA) study.

Participants filled in questionnaires regarding the amount of TV they watched and the amount of exercise they carried out. Data was collected every 2-5 years, between 1985-2011.

Over the 25-year period, the participants were asked about their TV viewing time and any physical activity they were involved in.

At the end of the 25 years, each participant completed a battery of three cognitive tests:

• Digit Symbol Substitution Test (DSST): this tests processing speed and executive functioning (regulation and control of cognitive processes including memory, reasoning, task flexibility, problem and planning)
• Stroop test: also testing executive function
• Rey Auditory Verbal Learning Test (RAVLT): assesses verbal memory.

Did TV make people cognitively slower?

The study found that those who moved around less physically and spent more time in front of the TV had worse scores in the DSST and Stroop tests but not the RAVLT.

The study authors concluded:

"We found that low levels of physical activity and high levels of television viewing during young to mid-adulthood were associated with worse cognitive performance in midlife.

In particular, these behaviors were associated with slower processing speed and worse executive function, but not with verbal memory.

Participants with the least active patterns of behavior (i.e., both low physical activity and high television viewing time) were the most likely to have poor cognitive function."

The authors are upfront about the limitations of the study. They admit that there may have been some selection bias due to participant drop-outs over the 25-year period.

They also mention that levels of TV viewing and physical activity were collected via questionnaire, a method that has its own pitfalls. Another limitation mentioned by the authors is that the cognitive tests did not measure all of the potential domains of cognitive functioning.

The paper's authors round off their report with a call for more research. Now more than ever, this should be an area of concern, as they rightly mention:

"Regarding population-based health, the effect of sedentary behavior may be especially consequential because the use of screen-based technologies for work and leisure has increased in the past several decades."

To summarize the current research in this field: sit less, move more.

References:

1. Effect of early adult patterns of physical activity and television viewing on midlife cognitive function, Tina D. Hoang et al., JAMA Psychiatry, doi: 10.1001/jamapsychiatry.2015.2468, published online 2 December 2015.
Additional sources:
2.  CDC, Physical activity, accessed 2 December 2015.
3.  Does active leisure protect cognition? Evidence from a national birth cohort, Richards M et al., Social Science & Medicine, doi: 10.1016/S0277-9536(02)00075-8, published online February 2003, abstract.
4.  Sedentary behavior: emerging evidence for a new health risk, Neville Owen et al., Mayo Clinic Proceedings, doi: 10.4065/mcp.2010.0444, published online December 2010.