Bone is a living tissue that changes over the course of a lifetime. They are continually changing through an elegant process called remodeling, where new bone cells replace older or damaged bone cells. This, in its simplest terms is accomplished through the interaction of two different types of bone cells: osteoclasts break down and remove the older bone making way for osteoblasts to build new bone. Scientists estimate that through this process, the skeleton completely remodels itself every ten years
During early development in infants, the bones are not fully calcified. During the first several years of life, a baby’s bone becomes mineralized with calcium, making it strong and somewhat flexible. With calcium added, the bones begin to become the storehouse of the body’s supply of calcium.
The process of building strong, healthy bones begins early in life and continues into adolescence. During this time, the osteoblasts are more active than the osteoclasts, supporting the growing skeleton. Children between the ages of 9 and 14 will build more bone density than they will lose in their lifetime. And 80% of the skeleton is developed by age 20. Bone “growth” is complete and “peaks” by the time the individual is age 30.
Between age 30 until menopause (around age 51 in women and around age 70 in men), there is a balance between the osteoblast and osteoclast activity. At menopause, because of the reduction in estrogen, osteoclast activity (breaking down bone) out paces the osteoblasts ability to rebuild bone, resulting in a net loss of bone mass. During the five years around menopause, women can lose up to 25% of their bone density if they are not careful. Bone loss is caused by loss of sex hormones but can be aggravated by disease, certain medications or lifestyle factors such as a poor diet, smoking or alcohol use.