Reducing TV viewing to less than one hour a day ‘could prevent one in nine cases of coronary heart disease’

A major risk factor for coronary heart disease is sitting for long periods of time rather than being physically active

People who watched more than four hours of TV each day were at greatest risk of the disease (Getty)

Reducing TV viewing to less than one hour a day could prevent one in nine cases of coronary heart disease, according to new research.

Watching too much TV is associated with increased risk of heart disease – regardless of an individual’s genetic makeup.

But the new study, published in the journal BMC Medicine, shows that – assuming a causal link – 11 per cent of coronary heart disease cases could be prevented if people watched less than an hour of TV each day.

Coronary heart disease is one of the UK’s leading causes of death –responsible for around 64,000 deaths each year. In the UK, according to the British Heart Foundation (BHF).

One in eight men and one in 15 women die from the disease. People with coronary heart disease are twice as likely to suffer a stroke.

One of the major risk factors for coronary heart disease is a sedentary lifestyle – 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 more than 500,000 adults who have been followed for about 12 years.

The team of scientists – from the Medical Research Council (MRC) Epidemiology Unit, the University of Cambridge and the University of Hong Kong – created polygenic risk scores for each person.

This is their genetic risk of developing coronary heart disease based on 300 genetic variants known to influence their chances of developing the condition.

People with higher polygenic risk scores were at greatest risk of developing heart problems.

Those who watched more than four hours of TV per day were at greatest risk of the disease, regardless of their risk score.

Compared to those individuals, people who watched two to three hours of TV a day had a relative six per cent lower rate of developing the condition, while those who watched less than an hour of telly had a relative 16 per cent lower rate.

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

Leisure time spent using a computer did not appear to influence disease risk.

Study corresponding author Dr Youngwon Kim, assistant professor at the University of Hong Kong and visiting researcher at the MRC Epidemiology Unit, said: “Our study provides unique insights into the potential role that limiting TV viewing might have in preventing coronary heart disease.

“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.”

Dr Katrien Wijndaele from the MRC Epidemiology Unit 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 Organisation 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.”

She added: “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 research team say there are several potential reasons that might explain the link between TV viewing and coronary heart disease risk and, in particular, why no link was found with computer use.

They said TV viewing tends to occur in the evening following dinner, usually our most calorific meal, leading to higher levels of glucose and lipids, such as cholesterol, in the blood.

People also often snack more when watching telly compared to when surfing the web, for example.

The researchers said that viewing tends to be prolonged, whereas people using their computer may be more likely to break up their activity.