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Too much TV ups risk of death, cardiovascular events
  January 10, 2011 | Lisa Nainggolan
London, UK - People who spend two hours or more a day in front of a screen during their leisure time-primarily watching television-have more than double the risk of cardiovascular events over four years compared with those who spend less than two hours a day in front of a screen, even after adjustment of the findings for physical activity, new research shows [1].
This is the first study to examine the relationship between screen-based entertainment time and nonfatal cardiovascular events, lead author Dr Emmanuel Stamatakis (University College London, UK) told heartwire. The results also show a 50% increased risk of all-cause mortality for those who sit in front of a screen for four hours or more a day compared with those spending less than two hours on this activity.
"I think there is a direct message from our research, which is that there should be a cutoff of two hours daily screen time as a maximum during leisure hours."
The results, say Stamatakis, are important. "This is a new research area, which has attracted attention only in the past 18 months to two years, but it has implications both for public-health recommendations and clinical guidelines. I think there is a direct message from our research, which is that there should be a cutoff of two hours daily screen time as a maximum during leisure hours." In fact, such guidance already exists for children in Australia, he says, adding that it could now be extended to apply to adults. And recommendations for adults in the UK [2] and the US [3] "do make references to sitting and TV," he notes, "but they don't set a threshold."
The findings could also help stimulate discussion with regard to what clinical advice doctors should be giving on this subject, he notes. At the moment, "one survey showed that in 55% of consultations, GPs did not even mention physical activity, which is a lot more well-established as being beneficial, so I don't think doctors are even aware they should be giving advice on sedentary time." But given how difficult it is to get people to exercise, it might be possible to reduce the cardiovascular risk of people who do not participate in sports by restricting sitting time and increasing nonexercise activity, such as standing, say he and his colleagues.
Further studies needed to determine exact mechanisms
In their study, Stamatakis et al followed 4512 respondents aged 35 and older from the Scottish Health Survey from 2003 to 2007 and assessed them for all-cause mortality and CVD events (fatal and nonfatal combined). The information on sedentary time was taken from a question about how much time participants spent in front of a screen during leisure time, both during the week and on weekends and averaged out to a screen-time-per-day exposure. Participants were put into one of three categories: less than two hours of screen time a day, two to less than four hours per day, or four hours or more per day.
Stamatakis said that leisure time was chosen because there is no overlap with employment: many people spend a lot of time in front of a screen at work, too, but this is much less modifiable than leisure time, he explained. And prior research has shown that the "number-one activity outside of work that people engage in is watching TV," he notes.
There were 215 CVD events and 325 any-cause deaths during the four years of following up (19 364 follow-up person years). The adjusted hazard ratio for all-cause mortality, including adjustment for physical activity, was 1.48 for those engaging in four hours or more of screen time relative to less than two hours, and for CVD events, the adjusted HR was 2.25. And the hazard ratio for those with two to four hours of screen time a day was similar to that of those who spent more than four hours a day in front of a screen, relative to those who spent less than two, Stamatakis noted.
The researchers found that approximately 25% of the association between screen time and CVD events was explained collectively by C-reactive protein, body-mass index, and high-density-lipoprotein cholesterol. The remaining 75% could be attributed to other factors that were not considered, such as diet and psychological factors, says Stamatakis. "Further experimental studies will be needed to determine the exact mechanisms," say he and his colleagues.
"Our results support the inclusion of a sedentary-behavior guideline in public-health recommendations for CVD prevention," they conclude.
1. Stamatakis E, Hamer M, Dunstan DW et al. Screen based entertainment time, all-cause mortality, and cardiovascular events. Population based study with ongoing mortality and hospital events follow-up. J Am Coll Cardiol 2011; 57: 292-299.
2. O'Donovan G, Blazevich AJ, Boreham C, et al. The ABC of physical activity for health: A consensus statement from the British Association of Sport and Exercise Sciences. J Sports Sci 2010; 28:573-591.
3. US Department of Health and Human Services. 2008 Physical Activity Guidelines for Americans
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