Why sitting may be bad for your heart

Sitting quietly for extended periods of time could be hurting your heart, according to a surprising new study. It finds that the more people sit, the greater the likelihood that they will show signs of injury to their heart muscles.

People who sit for more than about nine or 10 hours each day — a group that includes many of us who work in offices — are prone to developing diabetes, heart disease and other problems, and most of these risks remain relatively high, even if we exercise.

Excessive sitting also has been associated with heart failure. But how sitting, which seems to demand so little from the heart, could be linked to this has been unclear. So recently a group of cardiologists from around the world began to wonder about troponins. Troponins are proteins produced by cardiac-muscle cells when they are hurt or dying. A heart attack releases a sudden tsunami of troponins into the bloodstream.

But even slightly elevated troponin levels, lower than those involved in heart attacks, are worrisome if they persist, most cardiologists believe. Chronically high troponin levels indicate that something is going wrong inside the heart muscle and that damage is occurring and accruing there. If the damage is not halted, it could eventually result in heart failure. No research, however, had ever examined whether sitting was associated with high troponin levels.

So for the new study, published in Circulation, the researchers turned to existing data from the Dallas Heart Study, a large, ongoing examination of cardiac health among a group of ethnically diverse men and women, overseen by the University of Texas Southwestern Medical Center.

The researchers pulled information about more than 1,700 of these participants, excluding any who had heart disease or symptoms of heart failure.

Many of the study participants turned out to be sitters, remaining sedentary for as much as 10 hours or more on most days. They rarely exercised. Some did work out, though, usually by walking. And this physical activity, limited as it was, was associated with relatively normal levels of troponin. The people who moved the most tended to have lower amounts of troponin in their blood, although the benefits statistically were slight. On the other hand, the people who sat for 10 hours or more tended to have above-average troponin levels in their blood. These levels were well below those indicative of a heart attack, but high enough to constitute “subclinical cardiac injury,” according to the study’s authors.