Coffee tends to give us that quick pick-me-up. However after it's effects have worn off we tend to crave more to get to the same level of alertness. It also depletes calcium levels, and dehydrates the body from a western view. In TCM coffee consumes the kidneys in order to produce it's effects of mental alertness. Since bones are governed by the kidneys, it only makes sense that as our kidneys are consumed it leads to decreased bone density.