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CHAPTER 22   Osteoporosis
TOPICS   Osteoporosis
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Risk Factors for Osteoporosis

Primary osteoporosis: The longer a person lives, the higher the risk of osteoporosis. Bone density decreases partly because levels of hormones (such as estrogen and testosterone) decrease as people age. Estrogen, the main female hormone, helps prevent bone from being broken down and therefore helps keep it dense and strong. Testosterone, the main male hormone, stimulates bone formation.

Older women are affected by the decrease in hormone levels more dramatically than older men. Until menopause, bone density in women may decrease a little. But at menopause, the decrease in bone density speeds up dramatically because estrogen levels decrease rapidly. During the first few years after menopause, bone density may decrease by as much as 3 to 5% each year. After that, it decreases by about 1 to 2% each year. Thus, women are more likely than men to develop osteoporosis. Also, on average, women usually have lower bone density to begin with than men.

Women who have produced less estrogen before menopause are at even higher risk of developing osteoporosis. Such women include those who started menstruating late, reached menopause early, or had their ovaries surgically removed (a procedure called oophorectomy) before menopause.

As men age, testosterone levels usually decrease slowly. Testosterone levels may decrease abruptly if prostate cancer is treated by surgically removing the testicles or using drugs that prevent the testicles from producing testosterone. Men produce small amounts of estrogen. As men age, estrogen levels also slowly decrease. Men with low testosterone or low estrogen levels are more likely to develop osteoporosis.

Of racial groups, white people are most prone to osteoporosis. Asians are next, then Hispanics. Black people are less prone to osteoporosis, possibly because black people tend to have denser, stronger bones during young adulthood. Thus, they can better tolerate the decrease in bone density that occurs with aging and at menopause.

Thin people tend to have less dense bones than heavier people. Part of the reason is that body weight puts stress on bone, stimulating it to form more bone. Also, thin women may have lower estrogen levels than heavier women, because thin women usually have less body fat. Fat tissue produces some estrogen.

People who have close relatives with osteoporosis are more likely to develop it. The risk of developing osteoporosis is even higher when a relative has had a fracture related to osteoporosis.

People who do not consume enough calcium or who have vitamin D deficiency are also more likely to develop osteoporosis.

Physical activity affects the risk of developing osteoporosis. Bone is formed in response to weight-bearing activity (such as walking). Bone is broken down in response to inactivity. People who are less physically active throughout life are more likely to develop osteoporosis.

Smoking cigarettes increases risk because it interferes with the re-formation of bone.

Secondary osteoporosis: Disorders and drugs can cause osteoporosis by interfering with the body's absorption or use of calcium or vitamin D, by directly affecting the process of breaking down and re-forming bone (remodeling), or by doing both. For example, in hyperparathyroidism, the parathyroid glands produce too much parathyroid hormone. Normally, this hormone helps keep bone remodeling in balance. If too much parathyroid hormone is produced, more bone is broken down than re-formed, and calcium is removed from bone.

In Cushing's disease, the adrenal glands produce too much cortisol. Cortisol inhibits the cells that form bone. Thus, overproduction of parathyroid hormone or cortisol results in loss of bone density. Taking corticosteroids (such as prednisone), which act like cortisol, has the same effect. These drugs also decrease the amount of calcium that is absorbed from food and increase the amount of calcium lost in the urine.

An overactive thyroid gland (hyperthyroidism) produces too much thyroid hormone. Overproduction of this hormone speeds up the bone remodeling process, eventually resulting in loss of bone density. Thyroid hormones, taken to treat an underactive thyroid gland (hypothyroidism), can have the same effect.

In diabetes, more calcium is lost in urine. In inflammatory bowel disease, less calcium is absorbed from food. Rheumatoid arthritis and lupus (systemic lupus erythematosus) interfere with bone remodeling.

Anticonvulsants, such as phenytoin and phenobarbital, may interfere with the activity of vitamin D.

Back to Osteoporosis.

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