Excessive sitting is tied to all kinds of health problems, and a new, massive study finds that you can't counteract them with just an hour of exercise each day, though it still helps.
Toronto researchers pooled data from 41 studies and found that regardless of exercise regimen, prolonged sitting increases the risk of heart disease, diabetes, cancer, and death.
The review, out this week in Annals of Internal Medicine, showed that people who exercised regularly but sat for long periods had higher risk of serious illness or premature death. Those who didn't exercise often fared worse. The increased risks come from your activity levels across the entire day.
The definition of prolonged sitting ranged from eight hours a day to 12 hours or more in the studies the review analyzed. Really though, a person shouldn't be sitting more than four or five hours a day, the researchers say.
The biggest risk from sitting for long periods of time was a 90 percent higher risk of developing type 2 diabetes, according to the review. There was also a significant association between a sedentary lifestyle and breast, uterine, ovarian, and colon cancers.
A body functions differently when sedentary
Researchers also tried to get at the question: why is sitting so bad? Their best guess is that sitting for long stretches of time leads to metabolic changes in the muscles. They're still not well understood, but one likely explanation is that idle muscle cells release much lower amounts of lipase, an enzyme that's important for eliminating fats from the bloodstream and maintaining high levels of "good" cholesterol.
Another likely cause is that our bodies become more resistant to insulin when consistently sedentary. The expression of genes involved in suppressing inflammation is also altered when we sit, and may contribute to the increased cancer rates observed in people who sit a lot.
Ultimately, all of these mechanisms — along with others we still haven't detected — probably contribute to the insidious health cost of sitting all day.
You burn 50 fewer calories per hour when sitting
There's another, more obvious side effect spending a full day in a chair: you burn fewer calories sitting all day, compared to standing or walking. This is because your leg muscles need to work to keep you upright and balanced, expending some energy.
It varies widely from person to person, but it's estimated that you burn an extra 50 calories per hour when standing, compared to sitting. This might not sound like a lot, but it adds up if you sit for eight hours per day, five days a week.
Standing just half that time means you'll burn an extra 1000 calories each week without changing your diet or exercise. Do it for a year, and that's about 50,000 extra calories — the rough equivalent of running 15 marathons.
So what should you do?
The researchers recommend getting up to stand or walk for a few minutes every half hour. Pace while you're on the phone, have a standing meeting, or put your trash can further from your desk so you have to walk to it. If you want to try a standing desk, experts suggest taking sitting breaks to cut down on heel and knee strain.
At home, you can use commercial breaks to take a quick walk. Research has shown that people break up sedentary periods with short walking breaks have lower rates of obesity and other risk factors for diabetes and cardiovascular disease.