Underused Muscles, Underused Insulin
You may be inactive, but your pancreas didn't get the memo. The muscle inactivity that comes along with sitting disease has been associated with a decrease in your body's sensitivity to the insulin your pancreas makes, and that puts you at an increased risk of developing chronic diseases including metabolic syndrome (conditions associated with pre-diabetes) and type 2 diabetes (by about 7 percent) [source: University of Leicester]. Researchers are finding that women may be more at risk for this side effect of sitting than men.
Too much insulin in addition to higher levels of C-reactive protein and other chronic inflammation markers circulating in your sedentary body are also linked to certain cancers, such as breast and colon cancer (about a 10 percent risk increase) [source: Yates, et al]. It's theorized that when the body becomes less sensitive to insulin, levels build up in the body; the excess insulin in your body stimulates cell growth. It's also possible hours of sitting decreases production of antioxidants, which are the body's natural way of protecting itself against free radicals, known cell damagers (and cancer causers).