Watching TV for more than five hours a day doubles the risk of developing a deadly blood clot in the lungs, a new study shows.

More than 600,000 people in the U.S. suffer a pulmonary embolism each year, and more than 60,000 of them die.

Researchers at Japan’s Osaka University followed 86,024 men and women ages 40 to 79 for 18 years, tracking their TV habits and health.

They found that those who averaged more than five hours of TV viewing a day had twice the risk of fatal pulmonary embolism.

Surprisingly, the study showed that the risk was higher in people under 60 years old than it was for the elderly.

In people under 60, those who watched TV for five hours or more had six times the pulmonary embolism risk compare to those who watched less.

The researchers, who presented their findings at the ECS Congress 2015, said to lower risk TV viewers should take frequent breaks to stand up and walk around. They should also drink plenty of water to prevent dehydration.