"Sitting for long periods of time — when you don't stand up, don't move at all — tends to cause changes physiologically within your muscles," says Reynolds. "You stop breaking up fat in your bloodstream, you start getting accumulations of fat ... in your liver, your heart and your brain. You get sleepy. You gain weight. You basically are much less healthy than if you're moving."- Gretchen Reynolds, Interview with NPR
Reynolds recommends standing for two minutes every 20 minutes while desk-bound — even if you can't move around your office. "That sounds so simple," she tells Fresh Air's Terry Gross. "But that actually has profound consequences. If you can stand up every 20 minutes — even if you do nothing else — you change how your body responds physiologically."
Studies have shown that frequent standing breaks significantly decrease your chances of getting diabetes, she says. "If you can also walk around your office, you get even more benefits. You will lose weight, you lessen your chance of heart disease, and you will improve your brain. But if you can do nothing else, stand up!"
Edited on 2013-05-02 to remove a link to a related blog post from InsuranceQuotes that discusses the health dangers of inactivity.