Sedentary behaviors are classified as those that involve sitting for extended periods of time with little movement and low energy output. In day-to-day life, many people spend a lot of time sitting. Many office jobs require sitting all day at a desk, and some people spend hours a day in the car while commuting. After a long day, it is not uncommon to sit down to read, watch TV, or chat with friends. Even the hours eating around a dining room table are spent sitting. In fact, one survey estimates that children and adults in the United States spend 55 percent of their waking hours in sedentary activities. While it may not be surprising that sitting down is not the healthiest activity you can do, it may be shocking to hear that the dangers of sitting too long could actually shorten your life expectancy.
Even people who exercise regularly can be affected by sedentary behavior. It is important to realize that being physically active does not necessarily mean that you cannot be at risk for excessive sedentary behavior. In fact, you can be both a physically active person and a sedentary person at the same time. For example, perhaps you spend eight hours a day sitting at a desk for work. Although you may go on a run when you get home after work, the eight hours you spend sitting each day are not cancelled out by the fact that you exercise daily. Anyone who spends prolonged periods of time sitting, regardless of their overall activity level, is at risk for the dangers associated with sedentary lifestyles.
Sedentary lifestyles decrease life expectancy. Many studies have found a positive correlation between sitting and mortality from all causes.[1,2,3] These effects are seen regardless of general activity level of the individuals, and are pronounced in obese individuals. One analysis concluded that the life expectancy of the US population could increase by two years if adults spent less than three hours a day sitting.
Sedentary behaviors, including sitting and television viewing, are associated with increased mortality from cardiovascular disease.[1,3,4] Time spent sitting or watching TV is also associated with increased mortality from cancer, with an increased risk of breast, lung, prostate, colon, and endometrial cancers.[3,5,6,7] Additionally, sitting may increase your risk of type 2 diabetes, osteoporosis, and dementia.
Why Is Sitting so Bad For Us?
As one author puts it, “humans are not programmed to be physically inactive.” Indeed, the sedentary death syndrome is a major risk factor for numerous worldwide diseases and millions of premature deaths each year.  It is suggested that physical inactivity may accelerate the aging process. Sedentary behavior can directly influence metabolism, bone mineral content, vascular health, and can increase plasma triglyceride levels and decrease HDL cholesterol.
Strategies to avoid the dangers of sitting too long. If you spend much of your day sitting, find ways to get on your feet and move throughout the day. There is evidence that sitting for one prolonged period of time is worse than sitting that is broken up into smaller bouts by short interruptions.
At work, take short breaks regularly to walk around the office. Stand up for your lunch break, and if you can, meet with colleagues while making laps around the office or at least stand during a meeting. Put your computer on a high counter or bookshelf, or try out a stand-up desk that allows you to stand up while working. Some people even set up a desk on a treadmill so that they can walk while they work.
At home, avoid activities that keep you sitting for too long, and find things you like to do that keep your body moving. Find more ideas on how to stay healthy here.
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 Am J Epidemiol. 2010 Aug 15;172(4):419-29.
 Mayo Clin Proc. 2014 Jul 3. pii: S0025-6196(14)00382-6.
 PLoS One. 2013 Sep 26;8(9):e73753.
 Ann Clin Lab Sci. 2012 Summer;42(3):320-37.
 J Natl Cancer Inst. 2014 Jun 16;106(7).
 Appl Physiol Nutr Metab. 2010 Dec;35(6):725-40.
 Nutr Metab Cardiovasc Dis. 2014 May 2. pii: S0939-4753(14)00143-4.