Osteoporosis
Definition:
A condition which is characterized by the progressive loss
of bone density and thinning of bone tissue.
Causes, incidence, and risk factors:
Osteoporosis is the most common type of metabolic bone
disease in the U.S. There are currently an estimated 10
million Americans suffering from osteoporosis as well as another
18 million who have low bone mass. Osteoporosis occurs when
the body fails to form enough new bone or when too much of
the old bone is reabsorbed by the body, or both. Calcium and
phosphate are two minerals that are essential for normal bone
formation. Throughout youth, the body uses these minerals
to produce bones. If calcium intake is not sufficient, or
if the body does not absorb enough calcium from the diet,
bone production and bone tissues may suffer. Calcium and phosphate
may be reabsorbed back into the body from the bones, in which
case the bone tissue is made weaker. Both situations can result
in brittle, fragile bones that are subject to fractures
even in the absence of trauma (atraumatic fracture). Usually,
the loss occurs gradually over years. Many times, a person
will sustain a fracture before becoming aware that the disease
is present. By the time this occurs, the disease is in its
advanced stages and damage is profound.
While there are a number of causes of osteoporosis, hormone
deficiencies (estrogen in women and androgen in men) are the
leading cause. Women, especially over the age of 60, are the
most frequent sufferers of the disease. This is due to the
loss of ovarian function and subsequent reduction in estrogen
production that occurs at the time of menopause. Other causes
include corticosteroid excess (from Cushing's syndrome or
from prescribed exogenous steroids), hyperthyroidism, hyperparathyroidism,
immobilization, bone malignancies, certain genetic disorders,
and other miscellaneous problems such as low calcium in diet.
Researchers estimate that about 23% of American women over
the age of 50 have osteoporosis. In addition, 40% and 56%
of them have osteopenia, which is abnormally low bone density
that may eventually deteriorate into osteoporosis if not treated.
From these figures, researchers estimate that 50% of women
over the age of 50 will suffer a fracture of the hip, wrist
or vertebra. The risk of fracture in men of the same age group
is about 13%. In 1995, direct medical expenditures relating
to osteoporotic fractures totaled $13.8 billion. Risk factors,
in addition to menopause, include genetic and ethnic background.
Women who are white, especially those with a family history
of osteoporosis, have a greater risk of developing osteoporosis.
In fact, it is estimated that one out of two white women will
experience a fracture relating to osteoporosis at some point
in her life. Smoking, eating disorders, low body weight (less
than 127 lbs), low amount of calcium in the diet, heavy alcohol
consumption, and use of certain medications such as steroids
are also risk factors.
Usually, the loss occurs gradually over an extended period
of time (years) and most of the time, a person will sustain
a fracture before becoming
aware that the disease is present. By the time this occurs,
the disease is in its advanced stages and damage is profound.
Update Date: 05/08/00
Updated by: Ajay Nirula MD, PhD. Rheumatology
Fellow University of California at San Francisco Medical Center
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