Bone Health

The human bone is a remarkable organ. It provides the human body with various essential functions, such as serving as a support frame that provides structure and facilitates movement, providing protection of various soft tissues (i.e., spinal cord, brain), and serving as a reservoir for essential minerals, which are vital to maintaining normal physiologic homeostasis. These functions are influenced by a combination of internal body processes and environmental contributions. Abnormalities in either realm can lead to disease, which predisposes bone to becoming fragile and increases the risk of developing fractures.

Bone is composed of both organic and inorganic components. The organic portion is comprised of mainly proteins, whereas the inorganic component is made of minerals, which are calcium and phosphorous. The interaction between the minerals and the proteins gives the bone its characteristic strength. Overall, the human bone is a dynamic organ because it continuously changes its shape and size throughout a person's lifetime. This dynamic process, known as modeling and remodeling, involves making new bone and breaking down existing bone. The skeletal health of an individual is dependent on both processes.

An individual's overall bone health can be affected by internal factors, such as their genetic composition and hormones, as well as external factors. Genetic abnormalities include defects in bone production that result in thin bones, such as osteogenesis imperfecta, as well as defects in bone breakdown that result in dense bones, such as osteopetrosis. Environmental factors may stem from nutritional deficiencies, which can result in rickets, or from iatrogenic causes such as certain medications. In addition, irregularity of the hormonal regulatory mechanisms that balance bone homeostasis can also result in poor bone quality, as is often the case with patients who have chronic kidney disease and are dependent on dialysis. Regardless of the mechanism, poor bone health leads to bones that are fragile and thus prone to fracture.

Osteoporosis is by far the most prevalent bone disease worldwide. It is estimated that over 44 million Americans are at risk for osteoporosis, and 80 percent of those affected are women. While there are different types of osteoporosis, the most common form is age-related osteoporosis, which leads to changes in bone microarchitecture and decrease in bone mass. The overall result is bone fragility and propensity for severe fractures. The diagnosis of osteoporosis is established by screening with bone mineral density scans. Known risk factors that increase the likelihood of osteoporosis include being female, Caucasian or northern European descent, advanced age, estrogen deficiency, smoking, inactivity, malnutrition, and use of specific medications such as steroids or anticonvulsants.

The importance of good bone health is illustrated by the impact of osteoporosis on both the individual and society. The most significant consequence of osteoporotic bones are fractures. It is estimated that over 1.5 million osteoporotic-related fractures occur in the United States annually. These fractures can be devastating and may not only decrease an individual's quality of life, but also raise mortality risk. In addition, osteoporotic fractures incur significant societal costs in [Page 281]healthcare expenditures and loss of productivity. The estimated direct healthcare expenditure for osteoporo-sis-related fractures is $12.2–$17.9 billion annually.

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