Prolonged inactivity can cause blood to collect in the legs
“Binge watching TV can actually kill you, study finds,” The Independent reports in a somewhat exaggerated manner. The Japanese study its report is based on looked at prolonged TV watching and the risk of blood clots, and only found a very weak association.
Researchers were specifically looking at deaths caused by pulmonary embolisms – blockages in the blood vessel that carries blood from the heart to the lungs.
The study included more than 80,000 adults aged between 40 and 79 from Japan. Researchers estimated that people who regularly watched more than five hours of TV a day were two and half times more likely to die of a pulmonary embolism than those who watched less than two and a half hours.
While this may sound alarming it is important to realise that deaths from pulmonary embolisms are rare. Despite the large cohort, only 59 deaths occurred. And a modest increase in a rare risk means the risk remains rare.
The small number of deaths also means that any perceived association could have been the result of chance.
Also, the study design was unable to prove any cause and effect as many other factors may have been involved. That said, there is a growing body of evidence on the risks of sedentary behaviour.
The recommendation from the authors of the study, quoted in the media, that you get up and move around for a few minutes every hour while “binge watching” is sensible.
Where did the story come from?
The study was carried out by researchers from Osaka University Graduate School and was funded by the Japanese Ministry of Education.
Much of the UK media’s reporting of the study was as overblown as a season of 24 and did not mention the many limitations of the study. For example, The Independent’s headline “Binge watching TV can actually kill you, study finds” is incorrect. The study found no such thing.
It was good to see advice reported in some quarters to ensure you move around for a few minutes each hour.
What kind of research was this?
This study used data from a large cohort study to assess the link between the number of hours spent watching the television and the risk of death from pulmonary embolism.
Pulmonary embolism is a when a blood clot gets trapped in the blood vessel that takes blood from the heart to the lungs. It usually follows a clot in one of the leg veins (deep vein thrombosis or DVT) that has travelled through the blood to the heart.
As DVT is associated with prolonged immobility the researchers wanted to know whether watching TV (or, as is increasingly the case, streaming content to a tablet) could be associated with these outcomes.
This cohort study followed participants for a long period of time to draw observations, however, due to the design and the overall rarity of the outcome, the study cannot prove that one directly causes the other.
What did the research involve?
The researchers collected data from the Japanese Collaboration Cohort study, which began in 1988 and included adults aged 40 to 79 from 45 regions in Japan.
Participants were excluded if they had incomplete data on time spent watching TV or those with a history of cancer, stroke, myocardial infarction (heart attack), or pulmonary embolism at study start.
Information on potential confounders was collected by a self-administered questionnaire and included:
- body mass index
- history of hypertension (high blood pressure) or diabetes
- smoking status
- perceived mental stress
- educational level
- walking activity
- sports activity
Participants were categorised according to the time they spent watching television each day, these were:
- less than two and a half hours
- between two and a half and five hours
- five hours or more
The death certificates of participants were examined and the number caused by pulmonary embolism was recorded up to 2009.
Statistical analyses were performed for patients with complete information and were adjusted to take into account the effects of confounding.
What were the basic results?
The analysis featured 86,024 participants who were followed, on average, for 19.2 years. During this time 59 deaths from pulmonary embolism were recorded. Nineteen of them occurred in the people who watched TV for less than two and half hours, 27 in the second group, and 13 in the group who watched for five or more hours.
The amount of time spend watching television was associated with increased risk of death from pulmonary embolism.
Compared to the first group that watched less than two and a half hours, those who watched television for between two and a half and five hours were not at significantly increased risk death (hazard ratio (HR) 1.7, 95% confidence interval (CI) 0.9 to 3.0).
However, the third group who watched TV for more than five hours a day were two and half times more likely than the lowest duration group to die from pulmonary embolism (HR 2.5, 95% CI 1.2 to 5.3).
Overall, the data found that each additional two hours of television increased risk by 40% (HR 1.4, 95% CI 1.0 to 1.8).
How did the researchers interpret the results?
The researchers conclude: “our prospective cohort study suggests that prolonged television watching is a substantial risk factor for mortality from pulmonary embolism.”
This study used data from a large Japanese cohort study to assess the link between the number of hours spent watching the television and the risk of death from pulmonary embolism.
The study found that a greater number of hours watching the television increased the risk of death from pulmonary embolism.
The main strength of this study is the very large sample size and long follow-up periods. However, there are a number of limitations:
- this study design is not able to prove cause and effect, so while there appears to be a link, we cannot be sure the cause of mortality is from television watching
- even though the researchers attempted to account for relevant health and lifestyle factors such as BMI, smoking and physical activity, this may not be entirely accurate and there is still the possibility of residual confounding from these and other factors
- despite the large cohort size, death from pulmonary embolism is very rare. These deaths have then been further subdivided by TV category, and statistical comparisons that involve small numbers are less reliable
- the population was a group of older adults from Japan, the findings may not relate to other age groups or geographical populations
- mortality from pulmonary embolism was confirmed from death certificates. This is likely to be reliable, but we don’t know how many people may have experienced DVT or pulmonary embolism and not died from them
- information on the amount of time spent watching television was only collected on one occasion, this may have changed during the follow up period. People may also not be able to estimate with much accuracy how many hours they spent watching the TV, which may vary day to day
This study does however add to the growing evidence on the risks of sedentary behaviour. While much of the research in this area focuses on the relationship between sedentary behaviour and weight, some also suggests sedentary behaviour is independently associated with all-cause mortality, type 2 diabetes and some types of cancer.
The main issue considered in this study is the amount of time an individual spends watching television. But people are also sedentary at other times, such as when travelling, sat at a computer, or reading a book. The recommendation is to make sure that you get up and move around for a few minutes every hour.