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Osteoporosis
Boning Up on Osteoporosis
Boning Up on Osteoporosis
by Carolyn J. Strange
FDA
Consider an insidious
condition that drains away bone--the hardest, most durable substance in the
body. It happens slowly, over years, so that often neither doctor nor
patient is aware of weakening bones until one snaps unexpectedly.
Unfortunately, this isn't science fiction. It's why osteoporosis is called
the silent thief.
And it steals more than bone.
It's the primary cause of hip fracture, which can lead to permanent
disability, loss of independence, and sometimes even death. Collapsing
spinal vertebrae can produce stooped posture and a "dowager's
hump." Lives collapse too. The chronic pain and anxiety that accompany
a frail frame make people curtail meaningful activities, because the
simplest things can cause broken bones: Stepping off a curb. A sneeze.
Bending to pick up something. A hug. "Don't touch Mom, she might
break" is the sad joke in many families.
Osteoporosis leads to 1.5
million fractures, or breaks, per year, mostly in the hip, spine and wrist,
and costs $10 billion annually, according to the National Osteoporosis
Foundation. It threatens 25 million Americans, mostly older women, but older
men get it too. One in three women past 50 will suffer a vertebral fracture,
according to the foundation. These numbers are predicted to rise as the
population ages.
Osteoporosis, which means
"porous bones," is a condition of excessive skeletal fragility
resulting in bones that break easily. A combination of genetic, dietary,
hormonal, age-related, and lifestyle factors all contribute to this
condition.
Changing attitudes and
improving technology are brightening the outlook for people with
osteoporosis. Nowadays, many women live 30 years or more--perhaps a quarter
to a third of their lives--after menopause. Improving the quality of those
years has become an important health-care goal. Although some bone loss is
expected as people age, osteoporosis is no longer viewed as an inevitable
consequence of aging. Diagnosis and treatment need no longer wait until
bones break.
There is no cure for
osteoporosis, and it can't be prevented outright, but the onset can be
delayed, and the severity diminished. Most important, early intervention can
prevent devastating fractures. The Food and Drug Administration has revised
labeling on foods and supplements to provide valuable information about the
level of nutrients that help build and maintain strong bones. FDA has also
approved a wide variety of products to help diagnose and treat osteoporosis,
including several in the last few years.
Bone Life
Bone consists of a matrix of
fibers of the tough protein collagen, hardened with calcium, phosphorus and
other minerals. Two types of architecture give bones strength. Surrounding
every bone is a tough, dense rind of cortical bone. Inside is spongy-looking
trabecular bone. Its interconnecting structure provides much of the strength
of healthy bone, but is especially vulnerable to osteoporosis.
"We tend to think of the
skeleton as an inert erector set that holds us up and doesn't do much else.
That's not true," says Karl. L. Insogna, M.D., director of the Bone
Center at Yale School of Medicine, New Haven, Conn. Every bit as dynamic as
other tissues, bone responds to the pull of muscles and gravity, repairs
itself, and constantly renews itself.
Besides protecting internal
organs and allowing us to move about, bone is also involved in the body's
handling of minerals. Of the 2 to 4 pounds of calcium in the body, nearly 99
percent is in the teeth and skeleton. The remainder plays a critical role in
blood clotting, nerve transmission, muscle contraction (including
heartbeat), and other functions. The body keeps the blood level of calcium
within a narrow range. When needed, bones release calcium.
A complex interplay of many
hormones balances the activity of the two types of cells--osteoclasts and
osteoblasts--responsible for the continuous turnover process called
remodeling. Osteoclasts break down bone, and osteoblasts build it. In youth,
bone building prevails. Bone mass peaks by about age 30, then bone breakdown
outpaces formation, and density declines.
The skeleton is like a
retirement account, but in our skeletal "account" we can deposit
bone only during our first three decades. After that, all we can do is try
to postpone and minimize the steady withdrawals. Osteoporosis is the
bankruptcy that occurs when too little bone is formed during youth, or too
much is lost later, or both.
"You've got to get as
much bone as you can and not lose it," Insogna says. "The most
important risk factor for osteoporosis is a low bone mass."
"The upper limit of bone
mass that you can acquire is genetically determined," says Mona S.
Calvo, Ph.D., in FDA's Office of Special Nutritionals. "But even though
you may be programmed for high bone mass, other factors can influence how
much bone you end up with," she says. (See "Reducing
Your Risk.") For instance, men tend to build greater bone mass,
which is partly why more women face osteoporosis.
But there's another reason.
With the decline of the female hormone estrogen at menopause, usually around
age 50, bone breakdown markedly increases. For several years, women lose
bone two to four times faster than they did before menopause. The rate
usually slows down again, but some women may continue to lose bone rapidly.
By age 65, some women have lost half their skeletal mass. Because the
changes at menopause increase a woman's risk, many physicians feel it's a
good time to measure a woman's bone density, especially if she has other
risk factors for osteoporosis.
"The best way to gauge a
woman's risk for osteoporotic fracture is to measure her bone mass,"
says Insogna.
Routine x-rays can't detect
osteoporosis until it's quite advanced, but other radiological methods can.
FDA has approved several kinds of devices that use various methods to
estimate bone density. Most require far less radiation than a chest x-ray.
Doctors consider a patient's medical history and risk factors in deciding
who should have a bone density test. The method used is often determined by
the equipment available locally. Readings are compared to a standard for the
patient's age, sex and body size. Different parts of the skeleton may be
measured, and low density at any site is worrisome.
Bone density tests are useful
for confirming a diagnosis of osteoporosis if a person has already had a
suspicious fracture, or for detecting low bone density so that preventative
steps can be taken.
"There's a profound
relationship between bone mass and risk of fracture," says Robert
Recker, M.D., director of the Osteoporosis Research Center at Creighton
University, Omaha, Neb.
Readings repeated at intervals
of a year or more can determine the rate of bone loss and help monitor
treatment effectiveness. However, estimates are not necessarily comparable
between machine types because they use different measurement methods,
cautions Joseph Arnaudo, in the Center for Devices and Radiological Health.
"You always want to go back to the same machine, if you can," he
says.
Another new test provides an
indicator of bone breakdown. FDA approved in 1995 a simple, noninvasive
biochemical test that detects in a urine sample a specific component of bone
breakdown, called NTx. Clinical labs can get results in about 2 hours. The
NTx test, marketed as Osteomark, can help physicians monitor treatment and
identify fast losers of bone for more aggressive treatment, but the test may
not be used to diagnose osteoporosis.
Expanding Treatment
Options
Physicians and patients now
have more treatment options than ever. Under FDA guidelines, drugs to treat
osteoporosis must be shown to preserve or increase bone mass and maintain
bone quality in order to reduce the risk of fractures. "We want to be
sure that the bone is normal or stronger than it was," says Gloria
Troendle, M.D., deputy director of the division of metabolism and endocrine
drug products in FDA's Center for Drug Evaluation and Research.
Before 1995, the only choices
were the hormones estrogen and calcitonin. While enthusiasm for new weapons
against osteoporosis is warranted, one of the old ones is still the top
choice.
"Estrogen remains the
first thing that women should consider," says Insogna, because the
hormone not only helps prevent osteoporosis, but also protects against heart
disease.
"If you think about
what's missing at menopause, it's the hormones," says Paula Stern,
Ph.D., a pharmacologist at Northwestern University Medical School, Chicago,
Ill.
Estrogen replacement therapy
is the best prevention for the drop in bone mass at menopause, and there are
more ways to take it than ever. But it's not for everyone. Because estrogen
increases the risk of certain cancers and other diseases, taking it may not
be appropriate, or it may be given in combination with another female
hormone, progesterone, which can also cause undesirable side effects. A
woman and her doctor need to carefully weigh the risks and benefits.
According to the National Osteoporosis Foundation, a woman's risk of
developing a hip fracture is equal to her combined risk of developing
breast, uterine and ovarian cancer.
Women who can't or don't want
to take hormones--some 30 to 50 percent--have other treatment avenues. For
example, calcitonin treatment became much easier when FDA approved a nasal
spray in the summar of 1996. Calcitonin, one of the hormones responsible for
regulating the level of calcium in the blood, inhibits osteoclasts, the bone
dissolvers. The drug, marketed as Miacalcin, is a potent, synthetic version
of the hormone, and has been shown to slow and reverse bone loss. The
stomach quickly destroys the drug, so before the spray was available,
calcitonin had to be injected every day or two.
Later in 1996, FDA approved
the first nonhormonal treatment for osteoporosis. Alendronate, marketed as
Fosamax, falls within a class of drugs called bisphosphonates, which hinder
bone breakdown remodeling sites by inhibiting osteoclast activity. In
clinical trials lasting three years, alendronate increased the bone mass as
much as 8 percent and reduced fractures as much as 30 to 40 percent,
depending on skeletal site. Lengthier studies are ongoing.
To avoid damage to the
esophagus, Fosamax should be taken according to instructions. These
instructions include taking the drug in the morning upon awaking and at
least a half hour before eating. The drug should be taken with 6 to 8 ounces
of water, and the person should remain upright for a half hour after taking
it. Fosamax should not be taken by people who cannot stand or sit upright or
who have disorders that prevent esophageal emptying into the stomach.
"All the drugs approved
so far are things that just stop bone turnover. They're not really
stimulating more bone production," says Troendle.
Bone mass increases because
even though osteoclasts can't start new remodeling sites, osteoblasts
continue filling in existing cavities. Increases in bone mass are most
pronounced in the first year or two after treatment begins, then taper off.
Any gain is helpful, even if it doesn't continue, because increases in bone
mass help reduce fracture risk. But experts would like to encourage even
greater gains.
Fluoride, known for fighting
dental cavities, stimulates bone building, but early studies in osteoporosis
patients found that the structure of the new bone was abnormal and weaker
than normal bone. Gastrointestinal side effects were also a problem.
Investigators are working to find a formulation and dosage regimen that will
result in building normal bone.
Drugs Not Enough
Calcium and vitamin D
supplements are an integral part of all treatments for osteoporosis.
Everyone should make sure they get enough of these two nutrients, but
especially women and others at risk for osteoporosis. Attention to diet and
exercise are important not only for treatment, but also for prevention.
"If you go to the doctor
and get a prescription, and that's all you do, you're probably not going to
be helped very much," Recker says.
Calcium intake is critical,
and those who need it the most--younger women and girls--don't get enough.
(See "Calcium (Ac)Counts.") But calcium
alone can't build bone. Without vitamin D, calcium isn't sufficiently
absorbed. Most people get enough vitamin D because skin produces it in
sunlight. But people confined indoors who have a poor diet--which includes
many older Americans--or who live in northern latitudes in winter may be
deficient.
A lifelong habit of
weightbearing exercise, such as walking or biking, also helps build and
maintain strong bone. The greatest benefit for older people is that physical
fitness reduces the risk of fracture, because better balance, muscle
strength, and agility make falls less likely. Exercise also provides many
other life-enhancing psychological and cardiovascular benefits. Increased
activity can aid nutrition, too, because it boosts appetite, which is often
reduced in older people. The biggest reason older people don't get enough
calcium, Recker says, is that they simply don't eat much.
"The truth is, you don't
have to do very much to get most of the benefits of exercise," Recker
says. He suggests 30 minutes of brisk walking five days a week. Add a little
weightlifting, and that's even better. It's always smart to ask your doctor
before starting a new exercise program, especially if you already have
osteoporosis or other health problems.
Brighter Horizons
"A number of new things
seem to be in the offing, eventually to come to us, and we're looking
forward to getting some additional treatments for osteoporosis," says
Troendle.
Uses of existing drugs may be
broadened. Early drug trials are often conducted with patients who have
severe disease, often after a fracture has occurred or bone loss is quite
serious. Some studies under way are testing to see if certain drugs are
effective in less severe cases, if they can be started sooner, or used in
combination.
The search for bone-building
drugs continues. Some naturally occurring bone-specific growth factors have
been identified and their use as drugs is being investigated. "The way
I visualize the ideal future is that we'll be able to give Drug X that
builds up bone to where it's stronger and the risk of fracture is no longer
present, then Drug Y maintains it by preventing breakdown," says Stern.
In the realm of devices,
researchers are exploring the use of ultrasound to assess bone health. Such
tests would eliminate radiation exposure and probably cost less. The study
of risk factors also continues. "We consider that to be the research
that has the greatest public health significance," says Sherry Sherman,
Ph.D., of the National Institute on Aging. The institute has begun the Study
of Women's Health Across the Nation, a large-scale national examination of
the health of women in their 40s and 50s. Researchers expect to learn a
great deal about the factors affecting women's health during these
transitional years and beyond. Studies of genetics, biochemical markers, and
life habits are already turning up new insights.
Osteoporosis has been
described as an adolescent disease with a geriatric onset, highlighting the
importance of beginning to take steps--in exercise and diet--early in life
to reduce its disabling impact in later years.
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