Osteoporosis is primarily the result of a decline in osteoclast activity while osteoblast activity continues at expected levels. This imbalance leads to a net loss of bone density, as osteoblasts (the cells responsible for building new bone) are less active in comparison to the breakdown of bone by osteoclasts (the cells that remove bone tissue).
In a healthy bone remodeling process, osteoclasts and osteoblasts work in harmony to maintain bone density. However, when osteoclast activity decreases, there is less breakdown of old bone, but if osteoblast activity is not increased to compensate, the result is an accumulation of old bone without the formation of new, healthy bone. Over time, this leads to brittle and fragile bones characteristic of osteoporosis.