Sitting for three hours per day or longer may reduce an individual s life expectancy. A study calculated that limiting the time people spend sitting to 3 hours or fewer each day would increase the life expectancy of the population by two years. Cutting down TV watching to fewer than two hours each day would bump life expectancy up by another 1.4 years. When you are sitting your leg muscles are completely inactive which causes problems with how you handle your blood sugar and how you handle cholesterol.