Don’t spend workdays in your chair and evenings on the couch, even if you exercise every day.

Here’s news you shouldn’t take sitting down: the more time you spend sitting each day, the greater your risk of heart disease. A new study suggests that people who sit for 10 or more hours a day are more likely to have a heart attack or stroke than those who sit five or fewer hours each day.

Those who sat for 10 or more hours a day had an 18% higher risk than those who sat for five hours or less, regardless of their level of physical activity. But exercise made a big difference. The least active women in the study who sat at least 10 hours a day had a 63% higher risk than active women who sat five or fewer hours a day.

The findings come from a 12-year study of postmenopausal women enrolled in the Women’s Health Initiative (WHI). Although there weren’t any men or young women in the study, “there is no reason to believe that prolonged sitting would not increase risk in all adults. Previous studies in other populations support this,” says Andrea K. Chomistek, a research fellow at the Harvard School of Public Health. Dr. Chomistek is first author of the multicenter study, published in the Journal of the American College of Cardiology.

How to cut your sitting risk

None of these studies was able to measure the exact cardiovascular benefits of sitting less. But an earlier WHI report suggested that women can lessen harm to their hearts from sitting by increasing their physical activity. That finding should apply to men as well.

The message from this line of research is that activity trumps sitting. That doesn’t mean you have to spend several hours a day exercising. Just taking breaks from sitting—by standing up and pacing or taking a short walk—might also lower sitting-associated heart risk. The more standing and walking you do, the better.

Sitting and heart disease

Although the WHI study included only women, other studies have explored the link between sitting and heart disease in men and mixed groups, with the same general results.

Earlier this year, a study of more than 63,000 Australian men found that those who sat four or more hours a day were more likely to have developed heart disease, diabetes, or another chronic disease than those who sat less than four hours a day, regardless of how active they were.

And a Canadian study of men and women found that those who sat for most of the day were 54% more likely to die over the next 11 years than those who sat less than half the time. This study, too, found that too much sitting can be harmful even for those who exercise regularly.