@johnny0313x – actually there is one effect of gravity on our bodies (although it isn’t made greater by sitting rather than standing). That is that over time the weight of our vertebrae gradually compress the disks in our backs, which is a part of the height loss we undergo as we age.
Many people swear by the hanging upside down bit to help regain the flexibility (and some of the height) lost by the constant downward pressure. It is called “Inversion Therapy” and folks have been doing it for centuries. However, it may not be all the supporters say it is:
“Inversion devices, according to Dr. Gary Brazina, an orthopedic surgeon and sports medicine specialist in Los Angeles, don’t actually reverse the effects of gravity or increase the space between vertebrae, though they may temporarily extend the spine and briefly relieve muscle spasm. Potential side effects from hanging upside down include bleeding into the retina and headaches. It can also make some back problems, as well as hypertension, worse.” ( http://healing.about.com/gi/dynamic/offsite.htm?zi=1/XJ/Ya&sdn=healing&cdn=religion&tm=16&f=20&tt=14&bt=1&bts=1&zu=http%3A//wellnessletter.com/html/wl/2001/wlAskExperts0901.html )
So actually the answer to your question appears to be some people think so.