I'm curious to know if using a standing desk for four to five hours a day (but not moving around much) is equally unhealthy.
Just look into literature on any standing occupation, not constrained to just standing desks. There are plenty of hazards to take into account.
There is a significant standing up hazard for women: heels.
Heels long time use will deform your spine, your knee, changes the muscles that are responsible for walking, and is responsible of more ankle sprains than anything else.