Boning Up on Osteoporosis
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.
There is no cure or proven preventive treatment for osteoporosis, 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. The FDA has also approved a wide variety of products to help diagnose and treat osteoporosis, including several in the last few years.
Osteoporosis has been described as a geriatric disease with an adolescent onset, highlighting the importance of beginning to take steps--in exercise and diet--early in life to reduce its disabling impact in later years.
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 it 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 in 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, since the volume of bone remains about the same.
The skeleton is like a retirement account for minerals, but in our skeletal "account" we can deposit bone faster than we withdraw it only during our first three decades. After that, withdrawals are greater than deposits, and all we can do is try to minimize the net loss. Osteoporotic fractures are the sign of 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., a calcium expert in the FDA's Center for Food Safety and Applied Nutrition. "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 mineral 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. The 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 an internationally accepted standard based on young Caucasian women. 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 preventive 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 in 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 FDA's Center for Devices and Radiological Health. "You always want to go back to the same machine, if you can," he says.
A newer technique for evaluating bone strength is ultrasound, and the FDA has approved several instruments for this purpose. "These machines use the same principles that are employed when using ultrasound to look at fetuses during pregnancy," says Leo Lutwak, M.D., Ph.D., of the FDA's Division of Reproductive, Abdominal, and Radiological Devices. "Although this measurement examines different properties of bone than do X-ray-based bone densitometers, the results are also useful for prediction of fracture." The devices for ultrasound measurement are cheaper and easier to use. This makes them available in more locations and allows evaluation for osteoporosis in many more subjects. "Because they don't use X-rays, they are safer and may be used for repeated examinations, even in pregnant women and children, so they provide a means for better public health practice," Lutwak says.
Another new test provides an indicator of bone breakdown. In 1995, the FDA approved 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 doesn't measure bone metabolism specifically, so it may not be used to diagnose osteoporosis.
Expanding Treatment Options
Physicians and patients now have more treatment options. 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.
An important treatment option became available to women in November 2002. Forteo (teriparatide) is the first treatment that stimulates new bone growth to increase bone mass. Forteo is a portion of human parathyroid hormone, which works in the body to regulate the metabolism of calcium and phosphate in bones. The treatment is given in daily injections and is approved for postmenopausal women who are at high risk for bone fractures.
The approval of this treatment comes with a strong caution from the FDA: In the pre-approval studies of Forteo using rats, there was an increase in the incidence of osteosarcoma, a rare but serious cancer of the bone. Because it's possible that women treated with Forteo could have increased risk for developing this cancer, doctors are advised to discuss this risk with their patients and be sure that it's the best treatment. Women who are prescribed Forteo receive an FDA-approved medication guide that explains the benefits and risks and gives other advice about how to use the treatment properly.
All other drugs approved for osteoporosis treatment act by slowing the turnover of bone, rather than stimulating new bone formation. Increases in bone mass are most pronounced in the first year or two after treatment with the drugs begins, then taper off. Any gain is helpful, even if it doesn't continue, because increases in bone mass help reduce fracture risk.
In the mid-1990s, the FDA approved the first nonhormonal treatment for osteoporosis. Alendronate, marketed as Fosamax, falls within a class of drugs called bisphosphonates. In clinical trials, Fosamax increased the bone mass as much as 8 percent and reduced fractures as much as 30 percent to 40 percent, depending on skeletal site.
To avoid damage to the esophagus, Fosamax should be taken according to the instructions. These instructions include taking the drug in the morning upon awaking and at least half an hour before eating. The drug should be taken with a glass of water, and the person should remain upright for half an 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.
Other drugs recently approved for the prevention and treatment of osteoporosis
are Actonel (risedronate), a bisphosphonate similar to Fosamax, and Evista (raloxifene),
a drug in a class known as selective estrogen receptor modulators, or SERMs.
Both drugs have been shown to reduce the risk for fracture of the spine.
Fluoride, known for fighting dental cavities, stimulates bone building, but studies in osteoporosis patients have found that the structure of the new bone was abnormal and weaker than normal bone.
While estrogen may be a good option for some women, new guidelines developed in 2003 by the FDA advise doctors to consider alternative treatments. These changes were prompted by studies indicating that women who take estrogen or estrogen with progestin products after menopause are at higher risk for other conditions, including cardiovascular disease and breast cancer. Because of this, estrogen-containing products should only be considered for women at significant risk of osteoporosis.
Drugs Not Enough
Calcium and vitamin D supplements are an integral part of all treatments for osteoporosis. At the same time, people who take supplements should keep in mind that it is possible to consume excess amounts of these and other nutrients. 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 most--younger women and girls--may not get enough. (See "Calcium (Ac)Counts.") But calcium alone can't build bones. Vitamin D is needed to help the body absorb calcium. Most people appear to get enough vitamin D because the skin produces it in sunlight. And many foods, such as milk products and breakfast cereals, are fortified with vitamin D. But older adults and people with little exposure to sunlight may need a vitamin D supplement.
A lifelong habit of weight-bearing 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.
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 Paula Stern, Ph.D., a pharmacologist at Northwestern University Medical School in Chicago.
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.
Many factors can affect your chances of developing osteoporosis. The good news is that you control some of them. Even though you can't change your genes, you can still lower your risk with attention to certain lifestyle changes that will help build and maintain bone mass. The younger you start, and the longer you keep it up, the better.
Here's what you can do for yourself:
A sedentary lifestyle, smoking, excessive drinking, and low calcium intake all increase risk.
Other factors are beyond your control. Being aware of them can provide extra motivation and can help you and your doctor to make health care decisions. These risk factors are:
Risk factors may not tell the whole story. You may have none of these factors and still have osteoporosis. Or you may have many of them and not develop the condition. It's best to discuss your specific situation with your doctor.
Your skeletal calcium bank has to last through old age. Frequent deposits to this retirement account should begin in youth and be maintained throughout life to help minimize withdrawals. Recommendations for daily calcium intakes were established a few years ago by the Institute of Medicine. (See "How Much Calcium Do You Need?") Most women get much less calcium than they need--as little as half.
Nutritionists recommend meeting your calcium needs with foods naturally rich in calcium. Adequate calcium intake in childhood and young adulthood is critical to achieving peak adult bone mass, yet many adolescent girls replace milk with nutrient-poor beverages like soda pop. "Bone health requires a lot of nutrients and you're likely to get most of them in dairy products," says Connie Weaver, Ph.D., who heads the department of foods and nutrition at Purdue University. "They're a huge package rather than just a single nutrient." With so many low-fat and nonfat dairy products available, it's easy to make dairy foods part of a healthy diet. People who have trouble digesting milk can look for products treated to reduce lactose. A serving of milk or yogurt contains about 350 milligrams of calcium. Fortified products have even more.
"People who don't consume dairy foods can meet their calcium needs with foods that are fortified with calcium, such as orange juice, or with calcium supplements," says Mona S. Calvo, Ph.D., a calcium expert in the FDA's Center for Food Safety and Applied Nutrition. Other good sources of calcium are dark-green leafy vegetables like kale and turnip greens, tofu (if made with calcium), canned fish (eaten with bones), and fortified cereal products.
The food label can help you identify foods that are a good source of calcium and other nutrients important for bone health, such as vitamin D. You can use the Nutrition Facts found on the label to see if a food is a good source of these nutrients--that is, if it has at least 10 percent of the Daily Value (DV) per serving. Also, if a food has at least 10 percent of the DV, the label may bear a claim that it is a good source of a nutrient. If it has 20 percent or more, the label can say that it is "high" in or an "excellent source." Some foods that are excellent sources of calcium may also bear a health claim about the role of diet and other factors in reducing the risk of osteoporosis.
But keep in mind that foods with smaller amounts (such as between 5 percent and 10 percent of the DV) can still make significant contributions to your daily calcium intake. This may be especially true if you often eat more than one serving of the food in a day, or if your actual serving size is typically larger than the one on the label.
Finally, remember that label values are based on a single Daily Value established by the FDA for food labeling purposes--1000 milligrams in the case of calcium. They do not take into account that some age groups have lower or higher recommendations for intake.
What about too much calcium? A few years ago, the Institute of Medicine established a level of 2,500 milligrams as an upper intake level for calcium for most people. While intakes considerably above this level may be safe for many, others may be particularly susceptible to calcium's potentially harmful effects at these levels. Those with higher sensitivities, such as people at risk of kidney stones, should discuss calcium with their doctors.
Calcium is critical, but even a high intake won't fully protect you against bone loss caused by estrogen deficiency, physical inactivity, alcohol abuse, smoking, or medical disorders and treatments.
Source: Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride. Institute of Medicine, Washington D.C.: National Academy Press, 1997
For More Information
National Osteoporosis Foundation
Osteoporosis and Related Bone Diseases National Resource Center (ORBD-NRC)
Older Women's League (OWL)
North American Menopause Society