Sitting quietly for extended periods of time may 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.
We all have heard by now that sitting for hours on end is unhealthy, even if we also occasionally exercise. 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, a condition in which the heart becomes progressively weaker and unable to pump enough blood to keep the rest of the body oxygenated and well. But how sitting, which seems to demand so little from the heart, could be linked to heart failure, a condition in which the heart cannot respond adequately to exertion, 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 or slowed, 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 study’s participants had completed cardiac testing, given blood samples and health information and worn activity trackers for a week.
The researchers pulled information about more than 1,700 of these participants, excluding any who had heart disease or symptoms of heart failure, such as chest pain or shortness of breath.
They checked the men’s and women’s blood samples for troponins and the readouts from their activity trackers to see how much or little they had moved most days.
Then they made comparisons.
Many of the study participants turned out to be sitters, remaining sedentary for as much as 10 hours or more on most days. Not surprisingly, those men and women rarely exercised.
Some of the men and women did work out, though, usually by walking. They were not exercising a lot, but the more exercise they undertook, the fewer hours they sat, on average.
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 they were high enough to constitute “subclinical cardiac injury,” according to the study’s authors.
This relationship remained strong, even after the researchers controlled for other factors that could have influenced troponin levels, including age, gender, body mass index and cardiac function.
Overall, sitting was more strongly associated with unhealthy troponin levels than exercise was with desirable amounts.
Of course, this was an observational study and can show only that sitting is linked to high troponin, not that it causes troponins to rise.
It also cannot explain how physical stillness might injure cardiac cells.
But the effects are probably indirect, says Dr. James de Lemos, a cardiologist and professor at U.T. Southwestern Medical Center who oversaw the new study.
“Sedentary behaviour is associated with obesity, insulin resistance and fat deposition in the heart, all of which can lead to injury to heart cells,” he said.
“The other side of the coin is what you are not doing while you are sitting,” he added. You are not moving. Although this study found little benefit from exercise in terms of improving troponin levels, that result is probably related to how little movement people were doing, he said.
“Most of the cardiovascular literature, including other work from our group, suggests that both exercise and being less sedentary are important,” he said.
He and his colleagues are conducting a number of follow-up studies to look at whether sitting less, exercising more, or both affect troponin levels and the risk for subsequent heart failure, he said.
But for now and especially as we plan New Year’s resolutions, “we should consider that reducing sedentary behaviour is an important part of a healthy lifestyle,” de Lemos said.
“Focus on both less sitting and more exercise,” he said. “Take the stairs. Park at the outside of the parking lot. Have walking or standing meetings.”