Sitting is the posture adopted by most working people. It is wise to have an understanding of what we all do so often for so long!
Sitting is meant to be loading the sit bones (ischium of the pelvis) but most often it is the sacrum and sometimes even the spine that we rest on. The spine is loaded during sitting. Recently some evidence suggested that some slouching is not bad for the body.
I beg to differ on this. The crucial thing to note is that breaks in between is the best way to avoid straining low back and pelvic area structures. Changing position often is the other strategy to help avoid over loading of a specific area.
The pelvis has a sit bone which is located along the center of the buttock. Sitting right, in my opinion loads up this area and that involves maintaining a neutral lumbar lodosis (lumbar curve). However there is a possibility of over extending at the lower thoracic or lumbar areas. That would counter all the benefits of good sitting. Therefore my advice is to visit a local physiotherapist to identify a neutral lumbar spine with adequate loading of the sit bone and also using a good chair.
I cant stress the fact that breaks every 40 minutes would be a better alternative than slouching at work!