Volvo and SAAB both did some rather extensive research into the effects of prolonged position on health, as related to cutting healthcare and injury treatment costs for their workers. When they plugged some buncha numbers into the machine, both found -- independently of the other -- that sitting required more energy than standing, and was harder on the musculo-skeletal system.
Sitting also contributes to long-term back issues. Easy fix is to get either a swiss ball, and use it as your chair with ram-rod straight posture, or get a knee chair, and again remain focused on posture.
Vladimir Janda, a physical therapy guru from Eastern Bloc days, asked a pointed question in a seminar I took of his: "When, in human history, did we ever do so much sitting through the course of our evolution?" We sit in cars on the way to work, at work, cars on the way home, then on the couch before going to bed and starting all over again. Before the advent of the chair, we squatted much more. Oddly, our body makes healthy adaptations in lengh-strength muscular relationships with squatting, that are the reverse of sitting.
Not to mention the positional constraints on functionality of the IVC in a stooped position, and the effects that has on blood pressure.