Osteoporosis

Bone is an unusual tissue in that it is continually under construction. Several cell types (other than osteocytes) remodel bone. Osteoblasts secrete bone matrix. Osteoclasts degrade bone matrix. They are large cells with many nuclei. Decreasing bone mass due to loss of calcium salts is a normal part of aging, but it can lead to osteoporosis, in which bones are likely to break. Ten percent of women have severe enough osteoporosis by age 50 to suffer bone fractures. Nearly 25% of all women develop osteoporosis by age 60, and by age 90, one-third of all women and one-sixth of all men have it.

In the United States alone, the total cost of osteoporosis and its associated bone fractures has been estimated to be over $6 billion each year. In addition to the economic cost, the bone fractures that result from osteoporosis often lead to considerable disability and in many cases can actually result in premature death.

Although in many cases the exact cause of osteoporosis cannot be pinpointed, in a number of situations it is known to be caused by a particular factor or condition. One such situation involves prolonged treatment with large doses of glucocorticoids antagonize the actions of Vitamin D, resulting in a Vitamin D deficiency, which in turn leads to a relative calcium deficiency.

Another factor known to cause osteoporosis is called immobilization.

• When a limb is placed in a cast, the immobilization can result in a localized loss of bone mineral in that limb.
• Also a result of neurologic deficit such as paralysis
• In the weightless condition of space travel, astronauts also suffer from a generalized osteoporosis. Although they are not immobilized, the lack of weight-bearing activity by their muscles and bones lead to osteoporosis.

Some other factors causing osteoporosis:

1. Ancestry and sex
2. Smoking (75% of all women with osteoporosis are smokers)
3. Excessive consumption of alcohol and/or caffeine

Treatments:

• In postmenopausal women, treatment with estrogen has proven effective, but increases the risk of endometrial (uterine) cancer
• Exercise is the safest and most inexpensive way to combat osteoporosis

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