After years of “sitting is the new smoking” headlines, it turns out the story is a bit more complicated, with some bouts of inactivity riskier than others, a new study has found.

It may have office workers breathing easier, but binge-watchers concerned.

Sitting for long periods of time while watching TV was associated with a greater risk of heart disease and premature death, while sitting at work didn’t have that same link, according to a study published Wednesday in the Journal of the American Heart Association.

“We were really surprised. Most of us in the field thought that sitting is sitting no matter what you do, and it’s harmful whether it’s at work or at home watching TV,” lead author Keith Diaz, an assistant professor of behavioral medicine at Columbia University in New York City, told TODAY.

“(But) it appears that what you do outside of your work time is what may really matter for your heart health.”

In fact, people who exercised in their leisure time eliminated the health risk linked with TV viewing, Diaz and his colleagues discovered.

Many people binge-watch TV every day.

The findings are based on data from almost 3,600 residents of Jackson, Mississippi, who were enrolled in the Jackson Heart Study.

The participants reported how much television they typically watched during the day, how often they sat at work and how much they exercised per week.

Almost a third, 31%, reported watching more than four hours of TV a day, which concerned Diaz: “That’s like binge watching every day,” he said. Almost half of participants, 43%, said they often or always sat at work.

After they were followed for a median of about eight years, those who watched the most TV had a 50% greater risk of experiencing a heart attack, stroke or early death compared to those who watched the least TV.

But there was no such link for people who spent the longest time sitting at work compared to those who sat the least. In fact, there's a growing body of research that has found no association between work sitting and health risk, the authors said.

The health risk of watching lots of TV vanished when people spent 150 minutes or more per week doing moderate-to-vigorous exercise — like brisk walking, running, swimming and cycling.

All of the participants in the study were African-American, but the authors believe the findings would apply across all races, Diaz said.

Why is sitting while watching TV more harmful?

The researchers had two guesses.

First, sitting at work is different than lounging around while watching TV because in an office, people often get up from their desk to go to a printer, a meeting room or a co-worker’s desk. Previous research has shown such brief moments of movement, or “activity snacks,” can offset sitting risks.

But at home, people may sit on the couch for hours at a time without moving.

Second, the timing of TV sitting may play a role.

“Most people in America go home, they have the largest meal of their day, which is dinner, and then they go and sit and watch TV for hours straight. The combination of a large meal and then sitting and not moving and doing anything with your muscles is just really toxic and harmful,” Diaz said.

That’s because muscles help regulate our blood sugar and lipid levels. But they have to be signaled to work so if a person doesn’t move, they don’t do their job.

“The metabolic engines go to sleep,” Dr. James Levine, an obesity researcher, told NBC News. That can lead to higher blood pressure, and increase a person's risk of diabetes and heart disease.

How to lower your sitting health risks: