Have you heard of latest risk factor for death, heart disease and cancer? It's got to be something exotic, right? Maybe a new form of cholesterol or a hidden retrovirus? No, I'm afraid it's called sitting.
Yes, sitting can be dangerous, very dangerous for your health and heart. That's right - researchers have found that few things in your lifestyle can influence your survival as how often your butt is on a chair or couch. One study, for example, found that every hour in front of the television was associated with an increased risk of death by heart disease, cancer and all causes of 18 percent, 9 percent and 11 percent, respectively.  Other work has shown that for every two hours sitting per day, your risk of diabetes goes up by 7% because your body uses less blood sugar. 
NOTE: Remember that anything hard on the heart is also hard - or should I say limp? - on your erections as well.
This was really sobering for someone like myself who is a computer jockey by day. The study went on to state that for those who watch four or more hours of television per day have an 80 and 46 percent increased risk of dying from cardiovascular disease and all causes, repectively. These are monster numbers. The television and the computer, if you sit at them for extended periods of time, are the equivalent of a multi-pack smoking habit!
So is this just a television thing? We all know that television sucks the life out of your brain, so perhaps it hits the rest of the bod just as hard? Actually, it's not the television - it's the act of sitting that does it. For example, researchers divided people into groups that sit 25, 50, 75 and 100 percent of the time and then followed them for 12 years. The results were remarkable: a dose-dependent rise in death from all causes and cardiovascular disease.  In other words, the more sitting, the more likely the participants were to die from cardiovascular disease or all causes.
Also, an interesting twist is that a recent study found that sitting, independent of activity level, was strongly correlated with total all cause mortality. Of course, the authors emphasized that physical activity is important, but they also pointed out that even physical activity cannot overcome a lifestyle of sitting around.  Men who sat more than 6 hours per day were 18 percent more likely to die (and women 37 percent). 
The answer to the above question probably has many question but here are two key ones:
a) Lipase Activity. It shuts off the activity of a key enzyme called lipase. Lipase is the enzyme that breaks down fat and, after an extended time of sitting, lipase activity plummets to as low as one tenth of its normal rate. One study showed that if lipase levels were increased in diabetically induced mice, they completely avoided elevated low cholesterol and triglycerides.  In other words, lipase activity is a powerful cardiovascular protection and may explain why rural, third world lifestyles are so heart protective.
b) Endothelial Dysfunction. Researchers have found that after two hours of sitting, your arteries literally begin to "numb." By that I mean that they lose their ability to expand which lowers blood pressure and increases blood flow. And I would add that endothelial dysfunction is the most common cause of erectile dysfunction.
Here are two likely solutions. Choose one and you should be able to spare yourself from the extreme negative impacts of sitting:
A. 60-75 Minutes of Moderate Exercise Daily. Does your gut tell you that the common sense solution to the negative health effects of sitting would be exercise? If so, your gut would be exactly right. The question, though, would be "how much?" This was debated and some of the early research showed that you cannot make up for extended periods of sitting time through daily exercise unless that exercise is broken up into increments throughout the day regardless of fitness or exercise levels. In other words, if you sit almost nonstop at work, commuting and/or in front of a television/computer, then an hour of exercise at the gym cannot compensate.  
However, a more recent review examined multiple studies and found that 60-75 minutes of moderate exercise per day could eliminate the negative health effects of sitting. This is fantastic news, because you have a relatively easy solution to a huge health issue associated with the Western lifestyle.
I do realize, however, that for some of you, 60-75 minutes may sound like a lot. However, keep in mind that "moderate exercise" includes brisk walking. You can go to the gym and walk and get something done on a treadmill. You can walk through your neighborhood - hopefully not in a pollute urban city though - and benefit. You can get an inexpensive treadmill for home use and get a little reading done. 
B. Five Minutes Every Hour. Previous study work indicated that the endothelial dysfunction issues could be overcome with just five minutes of walking every hour. The study found that even in health subjects sitting for one hour lowered endothelial function by 50%! Again, this will be hard on erections as well. However, the researchers discovered that they could completely overcome this effect by having the subjects walk five minutes of every hour. 
1) Circulation, Published Online Jan 11 2010, "Television Viewing Time and Mortality. The Australian Diabetes, Obesity and Lifestyle Study (AusDiab)"
2) Medicine & Science in Sports & Exercise, May 2009, 41(5):998-1005, "Sitting Time and Mortality from All Causes, Cardiovascular Disease, and Cancer"
3) Arteriosclerosis, Thrombosis and Vascular Biology, May 2009, 41(5):998-1005, "Overexpression of Human Lipoprotein Lipase Protects Diabetic Transgenic Mice From Diabetic Hypertriglyceridemia and Hypercholesterolemia"
4) American Journal of Epidemiology, Advance Access published online on July 22, 2010, "Leisure Time Spent Sitting in Relation to Total Mortality in a Prospective Cohort of US Adults"
6) Women's Health, Nov 2009, p. 133.
7) http://www.medscape.com/viewarticle/725341_3, "Too Much Sitting: The Population Health Science of Sedentary Behavior: Objective Assessment of Sedentary Time: New Findings"
8) Exercise & Sport Sciences Reviews, Jul 2010, 38(3):105-113, "Too Much Sitting: The Population Health Science of Sedentary Behavior"
11) Med Sci Sports Exerc. 2015 Apr; 47(4):843-9, "Effect of prolonged sitting and breaks in sitting time on endothelial function"