Process of osteoporosis. Illustration of an osteo- clast bone cell in action during removal of bone tissue. An osteoclast (blue, centre) is a giant multi-nucleated cell that normally breaks down the calcified matrix of bone (yellow) during bone growth and formation. In the disease of osteo- porosis, however, more of these cells form. Cells which would normally become osteoblast bone growth cells (pink) coalesce to produce osteoclasts. As a result, bones become brittle and less dense, with a greater risk of fractures. Osteoporosis is most common in post-menopausal women, attributed to a decline in ovarian hormone which helps maintain bone mass. Steroid treatment is effective.