Bone Development Over A Lifetime

Bone is constantly in a state of flux. This state of flux is the result of two opposing forces: bone formation and resorption. Bone formation begins in utero, and the acquisition and development of bone mass continues throughout childhood. During growth and development of the skeleton, the cells lying on the surface of the developing bones, called osteoblasts, stimulate bone formation (Fig. 1). At the same time, a second group of surface cells, called osteoclasts, are involved in the process of resorption (breakdown) of bone. Both cell types are affected by physical and environmental factors (4,5).

At puberty, acquisition of bone mass is accelerated. This accelerated process is believed to be approximately 95% complete by age 18. Beyond this age, the process slows with the remaining 5% deposited in the bone matrix into the third decade of life (4,6,7). It is during these phases of growth and development that adequate intake of bone-related nutrients (calcium, vitamin D, magnesium, phosphorus, protein, vitamin K, boron, manganese, copper and zinc) is vital to a lifetime of strong and healthy bones (8— 17).

During adulthood, from approximately the third decade of life to the onset of menopause in women at approximately 45 to 55 years of age, bone mass is considered stable and at its peak (18). With the onset of menopause, there occurs a rapid reversal of bone metabolism from acquisition to bone mass reduction. This is in response to declining estrogen levels, which initiate the menopausal process (4). This reduction process occurs in two phases. The first

Table 2. Osteoporosis Risk Factors

Genetic

Females

Asian or Caucasian individuals Family history of osteoporosis Small bone structure

Bone osteocytes growth factors

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