The study, published last month in BMC Medicine, suggests 11% of coronary artery disease cases could be prevented if a person went from watching more than two hours of TV a day to less than one hour a day.
People who watched television for less than an hour had a 16% lower rate of developing coronary artery disease than people who watched four hours or more per day, and people who watched two to three hours of television per day had a 6% lower risk. These findings held true regardless of a person’s genetic predisposition to heart disease.
Youngwon Kim, PhD, the lead researcher on the study and an assistant professor in the School of Public Health at the University of Hong Kong Li Ka Shing Faculty of Medicine, told Verywell that up to 40% of cardiovascular disease risk can be attributed to genetics. His team wanted to explore to what extent sedentary lifestyle habits influenced risk independently of genetics.
“[This study] provides strong evidence on the potential role that limiting time sitting and watching TV could play in the prevention of coronary heart disease,” Kim said.
Kim said looking at a computer screen did not seem to increase the risk of heart disease. But he clarified the study only looked at “leisure-time computer use,” not time spent at a computer screen for work, gaming, or watching videos.
To conduct the study, researchers from the University of Cambridge and the University of Hong Kong used data and genetic information collected from more than 370,000 people in the UK Biobank study cohort (which includes tissue samples from about half a million people who also completed questionnaires about their lifestyles and habits).
The participants’ blood samples were evaluated for 300 gene variants known to have a role in heart disease.
Less TV, Lower Risk?
The study did not provide definitive proof that there is a causal relationship between TV viewing and heart disease. However, Tracie Barnett, PhD, an associate professor in the department of family medicine at McGill University in Montreal and a national volunteer expert for the American Heart Association, told Verywell that the findings are “very compelling.”
Barnett, who was not involved in the study, noted that the link between more TV viewing and an increased risk of coronary artery disease—and the lack of a link between heart disease and using a computer or tablet—has been seen before.
Why Is TV Bad For Your Heart?
According to Barnett, there could be several reasons why television viewing has a negative association with heart disease that using a computer or tablet does not. For example, it’s common to see ads for food on TV, which could trigger people to eat more. Many people snack while they watch TV and may miss cues that they are full.
Barnett said that a person who is reading a book, texting, or talking on the phone is engaged and actively taking part in the activity. On the other hand, they’re more likely to be passively sitting while watching TV.
“I want to know for those that were watching less television, what were they doing instead?” said Barnett. “I would have been very interested in seeing where that time went, what was it replaced with.”
Kim added that TV watching also tends to be prolonged and happens after an evening meal. Blood levels of both glucose (sugar) and cholesterol could be affected by this pattern of eating and then being sedentary.
If you find you’re watching well over an hour of TV a day, Barnett said you don’t have to scale back all at once.
“Even if we’re going from five to four hours, or four to three, or three to two, that’s an improvement,” she said.
Barnett noted that the American Heart Association recommends people try to break up their TV viewing time—for example, by getting up from the chair every 15 or 20 minutes.
