Sitting, a new disease cohort

Had an exhausting day? Think you deserve to kick back and relax? Think again. If you’re like most people, you spend more than half of your waking hours sitting or inactive for long stretches of time—at work, at school, in the car or watching TV or another type of screen. Even eating three meals a day would keep you seated for several hours. Now the NIH and CDC are calling out the “sitters” as a risk factor that leads to early mortality and a myriad of other diseases. (I feel like most of you somehow know this already.)

Scientists estimate that Americans ages 12 and up now spend most of their time—about 8 to 10 hours a day—sitting and doing things that require very little energy. The groups who sit the most are teens and older adults.

What’s so bad about sitting? Sedentary behavior—which usually means sitting or lying down while awake—is an adaptive behavior. This means your body adapts to basically doing nothing, your muscle go slack and you are breathing less oxygen. Since it’s oxygen that uses up the energy from food, sitting is not going to burn calories between meals.

“Some of us are forced into sedentary type jobs, by school or by commuting,” says Dr. Donna Spruijt-Metz, who studies childhood obesity at the University of Southern California. “But research suggests that breaking up sedentary time with even short bouts of activity—like getting up from your desk and moving around—is associated with smaller waist circumference and other indictors of good health.” As a health coach with 25 years running my own fitness company, telling people to stand more and walk more is not a fitness program.

When you’re sitting, Matthews says, “muscle contractions go way down, and your body’s resistance to gravity decreases.” When you sit for long periods, your body adapts to the reduced physical demand and slows down its metabolism. When metabolism slows, you burn fewer calories and boost the chance that extra energy will be stored as fat.  “We found that even a low level of physical activity—equivalent to about 10 minutes a day of walking—was associated with a gain of almost 2 years in life expectancy. High levels of activity—equivalent to about 45 minutes a day of walking—were associated with a gain of 4 years or more,” says Moore.

The outcomes weren’t so positive for those who were both overweight and did no exercise. “People who were obese and inactive lost about 7 years of life compared to normal weight people who were active,” Moore says.

The many benefits of moderate to vigorous activity have been much studied. Moderate to vigorous exercise gets your heart pumping and boosts blood levels of “good” cholesterol. Moving at moderate to vigorous intensity also strengthens your bones and muscles and lessens your risk for a wide range of health problems, including stroke, diabetes, certain types of cancer, osteoporosis and arthritis.

Although the benefits of intense activity are clear, less is known about the long-term impact of sedentary behavior. Since most people engage in a range of activities throughout each day, it can be challenging to tease apart the effects that sitting and non-exercise activity can have over time.

“Sedentary behavior is not simply the opposite of physical activity,” says Dr. John Jakicic, who studies the biology of exercise at the University of Pittsburgh. “It’s not as if you’re either sitting and doing nothing or you’re physically active. There’s a gray zone that includes light activity,” such as standing up, casual walking or grocery shopping.

Today, mobile technologies—such as smart phone apps and electronic activity monitors—are helping scientists gather better data. Study participants wear these small devices all day long. They provide data on what people are actually doing as they move throughout their day.

“Is it really the sedentary behavior that causes harm? Or is it the lack of physical activity at the right intensity that’s the problem? I don’t think we have the answers yet,” says Jakicic. With the help of new technologies, Jakicic and others are working toward answers.