Watching too much TV is associated with increased risk of coronary heart disease regardless of an individual's genetic makeup, say scientists.
The researchers, from the Medical Research Council (MRC) Epidemiology Unit, University of Cambridge and the University of Hong Kong, 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 is sedentary behaviour – in other words, sitting for long periods rather than being physically active. To examine the link between time spent on screen-based sedentary behaviours like 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 including more than 500,000 adults who have been followed up prospectively for about 12 years.
The team created polygenic risk scores for each individual – 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 watching more than four hours of TV daily were at greatest risk of the disease, regardless of their polygenic risk score.
Compared with them, people who watched two to three hours 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.
Leisure time at a computer did not appear to influence disease risk.
“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 TV viewing could be a useful lifestyle change and help people with a high genetic predisposition to coronary heart disease, in particular, to manage their risk.”
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 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 watching TV increases risk of coronary heart disease, because of various potential confounding factors and measurement error, our work supports the WHO’s guidelines.”
There are several potential reasons that might explain the link between TV viewing and coronary heart disease risk, says the team – particularly, why no link was found with computer use. TV viewing tends to occur in the evening after dinner, usually our most calorific meal, leading to higher levels of glucose and lipids, like cholesterol, in the blood. People also often snack more when watching TV compared to when surfing the web, for example.
The research was funded by the Li Ka Shing Faculty of Medicine at the University of Hong Kong.
Genetic susceptibility, screen-based sedentary activities and incidence of coronary heart disease
Youngwon Kim, Shiu Lun Au Yeung, Stephen J. Sharp, Mengyao Wang, Haeyoon Jang, Shan Luo, Soren Brage, Katrien Wijndaele.
Published in BMC Medicine on 24 May 2022
Whether the associations of time spent in screen-based sedentary activities with CHD vary by genetic susceptibility is currently unknown. The objective of this study was to examine the interplay of genetic susceptibility to CHD and two prevalent types of screen-based sedentary activities (television [TV] viewing and computer use) for CHD incidence.
This prospective cohort study included 373,026 individuals of European ancestry without prevalent CHD/stroke from UK Biobank data. Genetic susceptibility to CHD was assessed using weighted polygenic risk scores, calculated by summing the number of risk-increasing alleles among 300 single-nucleotide polymorphisms, multiplied by their corresponding effect estimates. TV viewing and computer use were assessed through touch-screen questionnaires. CHD incidence (n=9185) was adjudicated over a median 12.6-year follow-up.
Compared with ≥4h/day of TV viewing, the hazard ratio of CHD was 0.84 (95% confidence interval [CI] 0.79–0.90) and 0.94 (0.90–0.99) for ≤1h/day and 2–3h/day of TV viewing, respectively, after adjusting for confounders including the genetic risk. CHD hazards were higher for medium and high genetic risk than for low genetic risk. Across all levels of genetic risk including high-genetic risk, ≤1h/day of TV viewing had lower CHD hazards, compared with ≥4h/day: no evidence of interaction between genetic risk and TV viewing (p value: 0.362). Estimates of the population attributable fraction (PAF) suggested that 10.9% (95% CI 6.1–15.3%) of CHD could be prevented if TV viewing time were reduced to ≤1h/day, assuming causality. The PAF values were relatively larger for medium-to-high genetic risk than for low genetic risk, although the CIs were wide and overlapping. No associations were observed for computer use.
Less TV viewing time was associated with lower CHD risk independently of genetic risk. Clinical trials targeted at individuals with high genetic susceptibility should consider reducing TV viewing as as a behavioural target for prevention of an early onset of cardiovascular events.
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