A new study builds on earlier evidence suggesting that spending too much of our leisure time in front of the TV or computer takes a serious toll on the health of our hearts — and our longevity. But the new research finds that too much screen time ups the risk for heart disease and death from any cause even more than previously thought.

Those who spent at least four hours in front of a screen every day had a 48% greater risk of dying from any cause than people who spent less than two hours.

The study followed over 4,500 people for a period of four years (all participants were over the age of 35). The participants reported on their screen time (TV, computer, and video games) outside of work; they also told researchers about their activity levels, and other lifestyle factors. Researchers ranked participants according to how much screen time they averaged: less than two hours per day, two to four hours per day, or more than four hours per day.

Those who spent at least four hours in front of a screen every day had a 48% greater risk of dying from any cause than people who spent less than two hours. Even more, participants spending more than four hours in front of the TV also had a whopping 125% increased risk of suffering a cardiovascular event like heart disease, heart attack, or stroke.

Incredibly, the results held true even after controlling for other factors, like body mass index (BMI), smoking, age, socioeconomic status, and, most surprisingly, activity level. This suggests that even exercise didn’t reverse the effects of spending too much time in front of a screen in one’s free time.

The authors suggest that it is likely the act of sitting that puts the heart at risk, rather than the screen time itself, which earlier studies have also suggested to be the case.

For this reason, the team wanted to look into the underlying biological changes that might account for the link between screen time/sitting and cardiovascular risk. They looked at several biological markers in the participants, including BMI, HDL ("good") cholesterol, and C-reactive protein (CRP), which is a known marker of inflammation. They found these three variables explained up to 25% of the connection between screen time/sitting and heart disease, which meets the criteria for being considered a mediating variable in the connection.

The authors stress that the study looked specifically at leisure screen time, and did not consider how much time people spent sitting in front of a computer at their jobs. They say that because so many people spend large parts of their work days sitting, reducing screen time in one’s free time might be considered a powerful way to reduce heart risk. It certainly can’t hurt to get up off the couch or away from the desk to make the best – and healthiest – use of your free time.