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Limit TV viewing to less than an hour a day to reduce coronary heart disease risk, say University of Cambridge researchers

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Limiting the amount of time we sit watching TV to less than an hour a day could reduce our risk of coronary heart disease, researchers at the University of Cambridge and the University of Hong Kong say.

Sedentary behaviour - sitting for long periods of time, rather than being active - is a major risk factor for coronary heart disease.

And the researchers say that regardless of an individual’s genetic make-up, watching too much TV is associated increases our risk.

Sedentary behavior increases our risk of coronary heart disease (56951988)
Sedentary behavior increases our risk of coronary heart disease (56951988)

In the study published this week in BMC Medicine, researchers at the Medical Research Council (MRC) Epidemiology Unit suggest that, assuming a causal link, 11 per cent of cases of coronary heart disease could be prevented if people watched less than an hour of TV each day.

The researchers examined data from the UK Biobank database, which contains anonymised genetic, lifestyle and health information from half a million UK participants. They explored 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,

They created polygenic risk scores for each individual, meaning they calculated their genetic risk of developing coronary heart disease based on 300 genetic variants known to influence their chances of developing the condition.

Those with higher polygenic risk scores are at greatest risk of developing the condition.

But the researchers found that people who watched more than four hours of TV per day were at greatest risk of the disease, regardless of their polygenic risk score.

Those who watched two to three hours of TV a day had a relative six per cent lower rate of developing the condition.

And those who watched less than an hour of TV had a relative 16 per cent lower rate.

These associations were independent of genetic susceptibility and the other known risk factors.

“Our study provides unique insights into the potential role that limiting TV viewing might have in preventing coronary heart disease,” said Dr Youngwon Kim, assistant professor at the University of Hong Kong, and visiting researcher at the MRC Epidemiology Unit, the study’s corresponding author. “Individuals who watch TV for less than one hour a day were less likely to develop the condition, independent of their genetic risk.

“Limiting the amount of time sat watching TV could be a useful, and relatively light touch, lifestyle change that could help individuals with a high genetic predisposition to coronary heart disease in particular to manage their risk.”

Leisure time spent using a computer did not appear to influence disease risk, the researchers found.

This apparent contradiction may be because TV viewing tends to occur in the evening following dinner, which is usually our most calorific meal, leading to higher levels of glucose and lipids, such as cholesterol, in the blood.

And people also often snack more when watching TV, compared to when using a computer TV viewing also tends to be prolonged, whereas computer use may be broken up.

Dr Katrien Wijndaele from the MRC Epidemiology Unit, last author of the study, said: “Coronary heart disease is one of the most prominent causes of premature death, so finding ways to help people manage their risk through lifestyle modification is important.

“The World Health Organization recommends reducing the amount of sedentary behaviour and replacing it with physical activity of any intensity as a way of keeping healthier.

“While it isn’t possible to say for certain that sitting watching TV increases your risk of coronary heart disease, because of various potential confounding factors and measurement error, our work supports the WHO’s guidelines.

“It suggests a straightforward, measurable way of achieving this goal for the general population as well as individuals at high genetic risk of coronary heart disease.”

The British Heart Foundation says coronary heart disease is responsible for around 64,000 deaths each year. In the UK, one in eight men and one in 15 women die from it, making it a leading cause of death.

And people with coronary heart disease are twice as likely to have a stroke.

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