February 9, 2023

First Washington News

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Prolonged TV watching linked with severe blood clots

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New research finds a link between prolonged TV watching and a higher risk of potentially fatal blood clots. Thomas Winz/Getty Images
  • Researchers examined the link between hours spent watching TV and the risk of potentially fatal blood clots.
  • They found that prolonged TV watching is linked to a 35% higher risk of developing venous thromboembolism (VTE) than watching TV for shorter periods.
  • The researchers say that their findings do not prove causation and that more research is necessary before making any conclusions.

The hardening or narrowing of arteries — through atherosclerotic cardiovascular disease (CVD) — and potentially fatal blood clots in the veins called VTE are related and share common risk factors, including obesity and smoking.

Studies have shown that prolonged sedentary behavior, or physical inactivity, is linked to an increased risk of vascular conditions such as CVD and VTE.

Watching TV is a significant part of sedentary leisure time. Research indicates a link between TV watching time and CVD. However, studies on the link between TV watching time and VTE have varied — some support the association, while others negate it.

An analysis of different studies looking at the link between TV watching and VTE could help researchers and the public better understand the risk factors for the condition.

In a recent study, researchers from Finland, Ghana, and the United Kingdom conducted a meta-analysis of three studies examining the link between TV watching time and VTE.

They found that watching TV for longer was associated with a higher risk of developing VTE.

“General findings highlight the need for everybody to be physically active,“ Dr. Setor Kunutsor, lead author of the study, told Medical News Today. “If you want to binge on TV viewing, take breaks in-between. Stand and stretch every 30 mins.”

“For people whose jobs involve sitting for long hours, take regular breaks in-between; they will need to also increase their physical activity levels, as there is evidence showing that higher volumes of moderate and vigorous activity can reduce, or even eliminate, the risks associated with sedentary behavior.”

– Dr. Kunutsor

The study appears in the European Journal of Preventive Cardiology.

Of 28 potential studies examining the relationship between watching TV and the risk of first VTE events, the researchers selected three published between 2016 and 2021.

Altogether, these studies included 131,421 participants from the United States and Japan. At the beginning of the studies, the participants were aged 54–65 years.

Average follow-up times ranged from 5.1 to 19.8 years. Across the studies, there were 964 VTE events.

All of the studies assessed for TV viewing times via self-reported questionnaires and also included information on established VTE risk factors, such as:

After analyzing the data, the researchers found that those who watched TV for more than 4 hours per day had a 35% higher risk of developing VTE than those who watched TV for less than 2.5 hours per day.

They also report that their results are independent of age, sex, BMI, and physical activity.

To explain their findings, the researchers write that as TV viewing involves immobilization, extended periods of this activity may increase VTE risk factors such as:

  • body weight, hypertension, and lipids
  • systemic inflammation
  • plasma viscosity and platelet aggregation
  • venous stasis, which occurs when prolonged sitting prevents blood from returning to the heart from the lower extremities

They also note that snacking on non-nutritious foods while watching TV may also have contributed to an increased VTE risk, although they did not assess diet in their study.

“There is probably a constellation of factors related to cardiometabolic factors and inflammation,“ Wendy J Brown, Ph.D., who is a professor at the School of Human Movement and Nutrition Sciences at the University of Queensland, Australia, and was not involved in the study, told MNT.

“But I guess that venous pooling, i.e., stasis, might be important — except that decreased venous return is more likely if people are sitting with feet on the ground and not lying down with feet up (but you can get venous pooling when standing still as well). Note too that a single episode of ‘prolonged’ sitting — such as we see in long haul flights — is also reported to be associated with VTE,” she added.

“The study by Kunutsor and colleagues suggests that the link between TV viewing and blood clots might be […] due to being immobilized, i.e., sitting for long periods of time,” said Dr. Aviroop Biswas, Ph.D., who is assistant professor in social and behavioral health sciences at the University of Toronto and was also not involved in this study.

“This might be possible as TV viewing habits might reflect most of a person’s daily sitting time, and sitting for long periods of time has been linked with inflamed blood vessels, reduced blood flow, and vascular dysfunction — all of which are linked to a higher risk of stroke. These links are likely to be stronger among people with low levels of physical activity (PA), as PA can reduce risks of inflammation and other stroke risk factors — though, the study did not examine this relationship.”

When MNT asked whether these findings might apply to being stationary in a more general sense, Dr. Kunutsor said: “[These results also apply] to people whose jobs involve being stationary for a long time — jobs that involve sitting for a long time. This is the reason why some employers encourage employees to stand and move about more regularly. The use of standing desks is very useful for such jobs. Even standing, which is the least active behavior, has been reported to be associated with health benefits compared with sitting.”

“I guess the issue of being sedentary for long periods is a hazard — there need not be a screen necessarily,” added Prof. Brown. “Some people sit for very long hours at work without interruption, [such as in factories], but we tend to think more about office and call center workers who sit in front of screens. Drivers of trains, buses, etc., also sit for long periods without interruption.”

“But I think prolonged and uninterrupted TV time might be a proxy for a different kind of lifestyle with many unmeasured confounders [such as diet]. In any case, it need not be TV. I think that, especially in COVID times, people may have been watching a lot of movies through channels other than TV,” she explained.

The authors conclude that prolonged TV watching might be linked to an increased risk of VTE.

The authors note that the study had limitations. Due to its observational nature, they say that their results do not prove cause and effect. Furthermore, as their analysis was only based on three studies, they recognize the need for further research in this area. They also say that the data on TV watching times may not be fully accurate, as they were self-reported.

“The study has a lot of limitations, and frankly, is not convincing evidence for a link between prolonged TV time and blood clots,” said Dr. Biswas. “All three studies also sampled older participants — age range 40+. As age is a risk factor for stroke, and participants were followed for 5 up to 20 years, it’s possible that there would have been a higher number of stroke cases than studies examining younger participants — and so the risks for blood clots might have been lower.”

“The three studies explored in the review did not consider important risk factors for stroke. For example, diet or blood sugar levels are not measured in the three studies. Diet, especially a diet that increases blood sugars, can negatively influence how our body breaks down blood sugars, which increases inflammation and risk of blood clots,” he explained.

“This is particularly important to examine, as one study is from Japan, and two are from the U.S. People from these countries have different diets, and we have no idea about how these differences contribute to their risks. There is also evidence of different risk of blood clots/stroke for men and women, though these were not factored into any of the studies or the review,“ he pointed out.

Prof. Brown agreed that there are limitations to the research. She said, “The most important concern [for me] is that although the three studies ‘adjusted for’ physical activity, this does not mean the effects are ‘independent’ of physical activity — so we don’t know if these effects were attenuated or eliminated in those who were highly active in leisure time.”

“And none of the studies considered what the participants were doing when they not engaged in ‘prolonged’ TV time. There are 24 hours in a day. If prolonged TV was 4 hours, then what the people were doing in the other 12 hours of ‘wake time’ is very important. Prolonged TV time may be a proxy for a generally sedentary lifestyle.”

– Prof. Brown

“I would guess that people who do at least 1 hour of at least moderate intensity physical activity each day might not be at increased risk of VTE! This was not adequately examined in the studies included here,” she concluded.