CAROLYN BECKER, MD: The reason we worry about osteoporosis is that bone remodels itself. It is constantly getting rid of the old and replacing it with new bone so that it's structurally sound and strong bone. As we get older, especially after age 30 or 35, for some reason the bone that gets eaten away to be replaced by new bone is not replaced by as much new bone, so there's a net loss of bone over the years. The remodeling process goes on very rapidly after menopause for women, and that's often a time when there is very rapid bone loss.
LISA CLARK: Why does that happen, do they think?
CAROLYN BECKER, MD: We think it's because the lack of estrogen sets up a dynamic within the bone so that the bone starts to be more resorbed, or eaten away, rather than built up. There are two kinds of cells that we find in the bone -- osteoblasts and osteoclasts. Osteoblasts build bone, osteoclasts are like little Pac-Men that eat away the bone and cause these craters to be formed. Lack of estrogen and various other hormonal changes, as well as aging, seem to affect this balance so that the bone cells eating away the bone for some reason overcome the cells that are forming new bone, so you have a loss of bone over time.
Now, there is a bit of an erroneous assumption that osteoporosis is just something that affects older women. Actually, you could say that osteoporosis starts in childhood.
