Reducing TV viewing to less than one hour a day could help prevent more than one in ten cases of coronary heart disease

Watching too much TV is associated with increased risk of coronary heart disease regardless of an individual’s genetic makeup, say a team of scientists at the Medical Research Council (MRC) Epidemiology Unit, University of Cambridge and the University of Hong Kong.

In a study published today in BMC Medicine, the researchers show that — assuming a causal link — 11% of cases of coronary heart disease could be prevented if people watched less than an hour of TV each day.

According to the British Heart Foundation, coronary heart disease is one of the UK’s leading causes of death, responsible for around 64,000 deaths each year. In the UK, one in eight men and one in 15 women die from the disease. People with coronary heart disease are twice as likely to have a stroke.

One of the major risk factors for coronary heart disease is sedentary behaviour — in other words, sitting for long periods of time rather than being physically active. To examine the link between time spent in screen-based sedentary behaviours such as TV viewing and leisure-time computer use, an individual’s DNA, and their risk of coronary heart disease, researchers examined data from the UK Biobank, a study that includes over 500,000 adults who have been followed up prospectively for about 12 years.

The team created polygenic risk scores for each individual — that is, their genetic risk of developing coronary heart disease based on 300 genetic variants known to influence their chances of developing the condition. As expected, individuals with higher polygenic risk scores were at greatest risk of developing the condition.

People who watched more than four hours of TV per day were at greatest risk of the disease, regardless of their polygenic risk score. Compared to these individuals, people who watched two to three hours of TV a day had a relative 6% lower rate of developing the condition, while those who watched less than an hour of TV had a relative 16% lower rate. These associations were independent of genetic susceptibility and other known risk factors.

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