Bone Modeling in Childhood and Adolescence
All people grow bone slowly during childhood. At the beginning of adolescence, a bone growth spurt occurs in response to a genetically programmed increase in growth hormones and the regulatory steroid sex hormones estrogen and testosterone. During the next half a dozen years, bone is being rapidly added to all parts of the skeleton through the process known as bone modeling. During modeling specialized bone cells, osteoclasts, remove bone from the skeleton and other specialized bone cells, osteoblasts, replace it. The principal characteristic of modeling is considerably more bone is added to the skeleton than removed. This results in a net gain of bone with each modeling cycle.
Modeling is bone’s method for shaping the skeleton into its adult form. The rapid addition of bone ceases in the late teens. At that point, the process of skeletal maturation begins and continues for the next decade or two. Growth in height ceases. Bone continues to be added slowly to the skeleton over this time but finally ends when a peak in bone calcium mineral content is reached. This is called the time of peak bone mass PBM. The PBM occurs at about age 35 in the spine and age 40 in the hip. It is an asynchronous event occurring at different times for different bones in the body but about the same time for paired bones like the right and left humerus.
Genetics, calcium, vitamin D, exercise, protein, and calorie nutrition are important determinates of PBM. For a child to achieve their genetically predetermined peak bone mass these modifiable imputes should be optimized. One reason for a child not reaching their potential PBM is developing a serious illness, being poorly nourished, or being treated with a drug that damages bone development like glucocorticoids. Studies have shown that exercise and a calcium rich diet during childhood and adolescence improve DXA bone density. Vitamin D3 adequacy during growth and development is an essential modifiable factor for bone and immune health that depends upon the child or teen taking a daily supplement. It is not possible for modern people to obtain an adequate quantity of the key nutrient from other than a supplement.