DENVER — The health effects of television-watching are worse than the effects of other sedentary activities, a new analysis suggests.
"We're starting to think TV could be unique," said Mark Pereira, PhD, from the University of Minnesota in Minneapolis.
In recent years, more and more studies have shown that people who spend a lot of time sitting run an increased risk for illness, even if they get regular exercise, he told Medscape Medical News. But many of these studies have lumped all kinds of seated activities together.
To assess whether some sedentary activities are more harmful than others, Dr Pereira and his colleagues analyzed data from the long-term Coronary Artery Risk Development in Young Adults (CARDIA) study (NCT00005130).
The CARDIA researchers followed 5115 black and white men and women who were 18 to 30 years of age in 1985 and 1986. All lived in Birmingham, Alabama; Chicago; Minneapolis; or Oakland, California.
Participants were selected so that there would be approximately equal numbers in the subgroups of race, sex, education, and age.
Waist circumference, blood pressure, and levels of fasting glucose, insulin, triglycerides, and high-density-lipoprotein (HDL) cholesterol were used to calculate a cardiometabolic risk score for each participant, which is an indication of risk for stroke, heart disease, and diabetes.
In a 2010 follow-up, 3211 CARDIA participants reported the time they spent each day engaged in six specific activities: watching television; using a computer for nonwork activities or playing video games; doing noncomputer office work or paperwork; listening to music, reading, or doing arts and crafts; talking on the phone or texting; and sitting in a car, bus, train, or other mode of transport.
People who spent more time engaged in these activities were significantly more likely than people who spent less time to be younger (49.8 vs 50.3 years), black, unemployed, and uninsured. They also had a significantly higher average body mass index, waist circumference, blood pressure, fasting glucose level, and insulin level, and a significantly lower level of HDL cholesterol. And they smoked significantly more and exercised significantly less.
People who spent more time engaged in these activities were also more likely to be female, to drink less, and to have higher triglycerides levels, although none of these were statistically significant.
Average cardiometabolic risk scores were lower in participants who spent less than 5 hours a day in the six sedentary activities than in those who spent 5 and 7.4 hours and in those who spent 7.5 hours (–0.22 vs 0.00 vs 0.12).
This association between overall sedentary behavior and cardiometabolic risk supports the pattern seen in other studies: greater health risks with more sitting.
The increase in cardiometabolic risk was much greater with television-watching than with any of the five other activities. This was true whether the sedentary activities were looked at in isolation (a single-variable model) or were adjusted to take the other activities into account (a partition model).
In the single-variable model, the associations between cardiometabolic risk and television, computer, reading, and telephone were significant (P < 0.05 for all). In the partition model, the only significant association was between cardiometabolic risk and television (P < 0.001).
Table. Change in Cardiometabolic Risk Score With a 2-Hour Increase in Daily Activity
|Sedentary Activity||Single-Variable Model||Partition Model|
|Doing computer work||0.03||0.01|
|Using the phone||0.04||0.01|
When Dr Pereira and his colleagues used an isotemporal model — in which one activity was swapped for another — they calculated that when participants played computer games instead of watching TV, cardiometabolic risk score decreased by 0.07 points (P < .05).
If TV time was replaced with reading, paperwork, or phone use, scores also dropped by 0.07. And if TV time was replaced with a long car ride, the score dropped by 0.09 (P < .05 for all).
When activities other than television were substituted for each other, there was no significant change in cardiometabolic risk.
It is not clear why watching TV causes more health risks than other sedentary activities, Dr Pereira said, but he has some theories.
One possibility is that people stay motionless for longer periods of time in front of the television. They might move around more when using the phone or playing on the computer, and they might shift positions more when reading or doing paperwork. And they might stop and get out of their cars more often than they get up from the sofa when they watch TV.
"You can also think about eating while watching TV," he explained. People can zone out in front of a basketball game or a movie and lose track of how many potato chips they've eaten.
"Or think about the types of advertising that promote sedentary activities and the Western diet," Dr Pereira added. And characters in TV dramas can make smoking and drinking alcohol seem appealing.
Perhaps public-health messages should recommend breaking up time in front of the television, he said. TV watchers can be encouraged to use the same devices and smart-phone apps that people with desk jobs use to remind them to get up and move around every half hour or so, or at least to change positions.
Previous studies have indicated that TV is worse than other types of sitting, said session moderator Alpa Patel, PhD, from the American Cancer Society.
"It highlights the need for us to understand what's different about TV — whether it's simply a measurement issue or whether there is something fundamentally different about the behavior," she told Medscape Medical News.
And although it is clear that sitting is a problem independent of exercise, it is not yet clear whether the biggest problem is the total amount of time spent sitting per day or the amount of time spent at one stretch without getting up, she explained.
The study was funded by the National Institutes of Health. Dr Pereira and Dr Patel have disclosed no relevant financial relationships.
American College of Sports Medicine (ACSM) 2017 Annual Meeting: Abstract 1912/5. Presented June 1, 2017.
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Cite this: Television-Watching Health Effects Worse Than Other Sitting - Medscape - Jun 05, 2017.