When I first heard that sitting too much was associated with chronic disease, I was extremely skeptical. Of course it is, I thought... people who sit more exercise less, they lose cardiovascular fitness, and they burn fewer calories throughout the day, setting themselves up to gain weight. It's not that sitting too much directly promotes disease, I thought; it must be all that goes along with it. It's the lack of exercise and the weight gain that's the real problem.
Welp, I was wrong (1). Turns out, we now know of specific molecular processes that take place when we sit, and they're distinct from intentional exercise. In fact, even if you get the "recommended" amount exercise, 30 minutes a day, you can completely undo those metabolic benefits by spending the rest of your day sedentary in a chair. Sitting continuously sets off a series of unwanted cellular mechanisms that immediately reduce your HDL and increase your triglycerides, two common risk factors for cardiovascular disease. Over the long term, we put ourselves at high risk for chronic disease, and that includes heart disease, high blood pressure, diabetes, and obesity.
The experimental studies have all been done on rats at this point, but the results are pretty startling. In one study in which rats were restricted access to running wheels or treadmills, physical inactivity rapidly produced a 22% reduction in HDL (that's a bad thing). This was seen on the very first day of inactivity and persisted as long as the inactivity continued.
In another experiment, radioactive triglyceride (fat) tracers were used to track their movement about the rat's body. When seated, important postural muscles cease to take up triglycerides from the bloodstream by 75%, increasing our blood level (again... bad). There was a silver lining though: when the rats were periodically allowed to walk on a treadmill, this unwanted process was mitigated. It was the long-term, persistent sitting that caused the problem.
The solution is simple on paper but not so simple in practice: move more. Most of us probably don’t realize how much we sit… every time we’re at the computer, when we’re in the car, when we’re on the subway, when we’re at the movies, when we’re watching TV, when we’re reading a book, when we’re eating… it’s a part of everyone’s life. There’s nothing wrong with relaxing and spending time in a seated position; just don’t overdo it. Of course there will be situations when we’ll be forced to sit all day. Luckily for us, simply getting up periodically to stretch and walk around can mitigate the nasty side effects we get from staying seated.
What’s the take home message in all of this? Just because you’re going to the gym a few times a week doesn't necessarily mean you’re doing your body good. You've still got 15 or so other waking hours left in your day that can’t be ignored. Be conscious of how much you sit, and do what you can to stay on your feet. Staying active throughout the day is just as important for your long-term health as intentional exercise at the gym!