Osteoporosis

Osteoporosis means porous bones. In people with osteoporosis, bones become less dense or more porous.

Because bones are less dense, they are very weak and more likely to break. However, not all people with osteoporosis break a bone,and not every older person who breaks a bone has osteoporosis.

Osteoporosis is common. In the United States, about 8 million women and 2 million men over 50 have osteoporosis. In millions of other women and men over 50, bone density (mass) is low but not low enough to be considered osteoporosis. These people have osteopenia (which means deficient bone). They are at risk of developing osteoporosis as they grow older.

Bones do not become porous overnight. Bones slowly begin to become less dense long before people reach old age. And the process continues as people age. Consequently, osteoporosis used to be considered an unavoidable part of aging. It was associated with becoming stooped over, breaking bones, and not being able to live independently. But now osteoporosis is recognized as a disorder that can be detected early, treated effectively, and often prevented.

See the figure Porous Bone: A Decrease in Bone Density.

To keep bones dense, the body needs an adequate supply of minerals (mainly calcium and phosphorus) and vitamin D. Minerals are incorporated into bones, making them dense and strong. This process is called mineralization. Vitamin D helps the body absorb calcium from food and incorporate it into bones. Calcium, phosphorus, and vitamin D can be consumed in foods. The body needs sunlight because vitamin D is formed when the skin is exposed to sunlight. To keep bones dense, the body also needs to produce appropriate amounts of several hormones. They include estrogen, testosterone, parathyroid hormone, and growth hormone. Calcitonin, another hormone, may play a role.

Bone is a constantly changing tissue. In response to the changing demands placed on bones, small areas of bone are continuously broken down and re-formed. For example, when physical stress is placed on bones, the body responds by forming more bone. The process of breaking down and re-forming bone is called remodeling. It occurs continuously in healthy bone.

Until about age 30 to 35, more bone is re-formed than is broken down, and bones progressively increase in density. Around this age, bones are at their densest and strongest. At some point after this age, bones begin to decrease in density slowly and progressively because more bone is broken down than is re-formed. Thus, as people age, bones become less dense, more fragile, and more likely to break.

Fractures due to osteoporosis are more likely to occur in some bones than in others. They include the thighbone (femur) at the hip, the arm bones (radius and ulna) at the wrist, and the bones of the spine (vertebrae), usually in the middle to lower back.

See the sidebar What Is Osteomalacia?

See the sidebar Vitamin D: Keeping Bones Strong.

Causes

There are two main types of osteoporosis: primary and secondary.

Primary osteoporosis, by far the most common type, has no specific cause but usually occurs in people over 50. Primary osteoporosis is more likely to develop in some people than in others. The following characteristics or conditions (called risk factors) make a person more likely to develop primary osteoporosis:

• Being middle-aged or older
• Being female
• Being white, Asian, or Hispanic
• Being thin
• Having close relatives with (a family history of) osteoporosis
• Consuming an inadequate amount of calcium
• Consuming an inadequate amount of vitamin D
• Spending an inadequate amount of time in sunlight
• Being physically inactive
• Smoking cigarettes

Drinking large amounts of alcohol may increase the risk of developing osteoporosis. However, consuming one to six drinks of alcohol a week does not seem to harm bones. If osteoporosis is already present, drinking large amounts of alcohol and smoking can make it worse.

Whether consuming a lot of caffeine increases the risk of osteoporosis is unclear. Consuming a lot may increase the amount of calcium excreted in urine. However, consuming a moderate amount of caffeine has only a small effect on bone density as long as enough calcium is also consumed.

Secondary osteoporosis is caused by a specific disorder or a drug. Disorders include inflammatory bowel disease, liver disorders, chronic kidney failure, rheumatoid arthritis, lupus (systemic lupus erythematosus), and hormonal disorders (especially hyperparathyroidism, Cushing's disease, hyperthyroidism, and diabetes mellitus). Drugs that can cause osteoporosis include corticosteroids (such as prednisone), thyroid hormones, phenytoin and phenobarbital (anticonvulsants), and cyclosporine (an immunosuppressant, taken to prevent rejection of transplanted organs). If primary osteoporosis is already present, these disorders and drugs can make it worse.

For additional detail on this topic, see Risk Factors for Osteoporosis.

Symptoms

Usually, osteoporosis does not cause any symptoms at first. The most common symptoms are pain and broken bones. People may not know they have osteoporosis until they break a bone, often after a slight jarring or a fall. Occasionally, a bone breaks for no apparent reason.

Some people lose height and become stooped with a bent back, called a dowager's hump (kyphosis). These changes may occur because the bones of the spine (vertebrae) gradually collapse within themselves and become squashed (compressed). This type of fracture is called a compression or crush fracture. Compression fractures may be painless or painful. Pain may develop gradually and be aching, or it may begin suddenly and be sharp. The shape of the chest and abdomen may change. As a result, clothes may be looser around the shoulders and chest and tighter around the waist. The changes in shape may put pressure on the lungs, heart, or intestine, and these organs may function less well.

See the figure How Osteoporosis Causes Stooping.

People with osteoporosis may break other bones, particularly the hip and wrist. Hip and wrist fractures often occur after a fall. A broken hip is especially serious. It can lead to loss of independence and function and to serious, even life-threatening problems. However, all broken bones in people with osteoporosis are serious, because bones that are less dense tend to heal slowly and sometimes incompletely. Also, if people with osteoporosis break one bone, they tend to break other bones.

Screening and Diagnosis

Screening involves measuring bone density before symptoms occur. All women over 65 should be screened for osteoporosis. Men over 65 who have low testosterone levels should also be screened for osteoporosis. Diagnosis involves checking for osteoporosis when doctors have a reason to think that it is present. For example, doctors should check for osteoporosis whenever an older person breaks a bone.

The most common and most useful test for measuring bone density is dual-energy x-ray absorptiometry (DEXA) scanning. It is used for screening and diagnosis. DEXA scanning is a safe, painless test that uses x-rays to measure bone density. Exposure to radiation is much less than that with a chest x-ray. The test takes about 15 minutes.

DEXA scanning provides two measures of how dense bone is: the T score and the Z score. The T score compares the person's bone density with the average bone density of 25- to 30-year-olds of the same sex. This age group is used because bone density is at its highest then. A T score of 0 means that bone density is the same as the average bone density of 25- to 30-year-olds. A score above 0 (a positive score) means that bones are more dense than the average. A score below 0 (a negative score) means that bones are less dense than the average.

The Z score compares a person's bone density with that of people of the same age, sex, and weight. Because bone density decreases with aging, bone density may be low in older people even when their Z score is average. Thus, this score is not as useful as T scores in determining the likelihood of breaking a bone and in making decisions about treatment.

DEXA scanning is usually used to measure bone density in the lower spine and hip and sometimes the wrist and forearm. Doctors measure bone density in more than one site because scores may vary from site to site. For example, a T score may be normal at the spine but low at the hip, or vice versa.

Ultrasonography (ultrasound) and computed tomography (CT) can also determine bone density. Ultrasonography is used primarily for screening. For example, portable ultrasound devices may be used at health fairs to scan the wrist, forearm, or heel. Special types of ultrasonography can be used to diagnose osteoporosis.

Computed tomography (CT) is used primarily for diagnosis. CT is particularly useful when changes in bone due to arthritis or old fractures make the results of DEXA scanning hard to interpret. Also, CT can help doctors identify or rule out other disorders (such as cancer) that can result in a broken bone.

After osteoporosis is diagnosed, blood and urine tests may be done. They can sometimes help determine how rapidly bone is being broken down and whether osteoporosis is due to another disorder.

See the table Interpreting T Scores.

Treatment

Ideally, early in life, people should make lifestyle choices to help keep bone density from decreasing and possibly to increase it. Making these choices early is important because bone density starts decreasing to some degree when people are in their 30s. These choices are particularly important for older people whether osteoporosis has been diagnosed or not.

Weight-bearing exercise done regularly may be the most important. Examples are walking, stair climbing, dancing, and weight training. In weight-bearing exercise, people support their entire body weight. The physical stress put on bones during this exercise stimulates bone formation and thus helps maintain or increase bone density. Usually, 30 minutes of weight-bearing exercise each day is recommended. Exercise that does not involve weight bearing, such as bicycle riding and swimming, does little to stimulate bone formation. However, exercise of any type improves muscle strength and balance, which can help prevent falls and the fractures that may result.

Consuming enough calcium and vitamin D helps maintain bone density. Older people should consume 1,200 to 1,500 milligrams (mg) of calcium and 600 to 800 international units (IU) of vitamin D every day—the amounts supplied by about four 8-ounce glasses of milk. Good sources of calcium include dairy products, tofu, broccoli, turnip greens, collard greens, and calcium-fortified juices. If a person does not consume enough calcium and vitamin D in foods and beverages, calcium and vitamin D supplements can be taken. Supplements are safe and inexpensive.

Spending time outside in the sun is another way to get vitamin D (because vitamin D is formed when the skin is exposed to sunlight). But older people cannot get enough vitamin D this way no matter how long they stay in the sun. Also, spending time in the sun becomes harder if older people have problems with walking.

Because smoking makes loss of bone density more likely, quitting or never smoking can help maintain bone density.

Drug treatment: For people who have low bone density or who have broken a bone, drugs that can prevent further decreases in density (and fractures) may be recommended.

A bisphosphonate (such as alendronate, etidronate, pamidronate, or risedronate) is the drug of choice for people who have low bone density. Bisphosphonates decrease the amount of bone being broken down. Men and women who take a bisphosphonate have fewer fractures of the vertebrae, hips, and wrists. These drugs are taken as tablets usually once a week but sometimes once a day. New bisphosphonates that can be given intravenously once or twice a year are being studied.

Foods and other substances in the digestive tract can prevent the body from absorbing bisphosphonates taken as tablets. So a person must take this drug with a full glass of water (6 to 8 ounces) on an empty stomach first thing in the morning. For the next 30 minutes, no other food, drink, or drug should be consumed. Also, bisphosphonates can irritate the lining of the esophagus. So after taking the drug, the person must sit up or stand for the next 30 minutes. People with disorders of the esophagus or a low calcium level in the blood should not take bisphosphonates by mouth.

Estrogen used to be widely prescribed to help maintain bone density in women after menopause and to treat women with low bone density. Estrogen prevents decreases in bone density and, in many women, increases bone density. Nonetheless, long-term use of estrogen for these purposes is no longer routinely recommended because such use has risks.

Because taking estrogen has risks, decisions about whether to use estrogen are complex. Use of estrogen alone increases the risk of cancer of the uterus (endometrial cancer) and may increase the risk of breast cancer. The risk of endometrial cancer can be reduced by taking a progestin with estrogen (hormone replacement therapy, sometimes called HRT). Progestins are drugs related to the female hormone progesterone. However, taking a combination of a progestin and estrogen increases the risk of breast cancer, coronary artery disease, stroke, and dementia. Estrogen, with or without a progestin, also increases the risk of blood clots, particularly for people who are already prone to developing clots, such as people who are temporarily or permanently confined to bed.

If treatment with estrogen is being considered, a woman should talk with her doctor, weigh the benefits and risks of estrogen, and compare all available options for maintaining bone density or treating low bone density.

Raloxifene belongs to a group of drugs called selective estrogen receptor modifiers (SERMs). Raloxifene resembles estrogen in some ways. Like estrogen, raloxifene prevents further decreases in bone density and, in some women, increases bone density. Women who take it have fewer fractures of the vertebrae. But raloxifene has not been shown to reduce the risk of hip or wrist fractures. Like estrogen, raloxifene has side effects and can increase the risk of blood clots. It has some advantages over estrogen because it does not affect the uterus or breasts. Raloxifene is prescribed for women who cannot or do not wish to take a bisphosphonate or estrogen.

Testosterone is used in men who have low testosterone levels. Testosterone can maintain or increase bone density.

Calcitonin, a hormone, can decrease the amount of bone being broken down. Calcitonin also seems to decrease pain due to fractures. But it is not as effective as bisphosphonates and other drugs for treating osteoporosis.

Teriparatide is a synthetic version of parathyroid hormone. The effects of teriparatide differ from those of parathyroid hormone. The continuous production of parathyroid hormone by the body helps balance the normal breaking down and reforming of bone. Because teriparatide is injected once a day, it stimulates the formation of bone more than the breakdown. Thus, it can help new bone form, increase bone density, and reduce the risk of fractures. The main disadvantage of this drug is that it must be injected. Its long-term effects are unknown.

Fluoride supplements should not be used to treat osteoporosis. They may increase bone density, but the resulting bone tends to be fragile. Fluoride supplements do not reduce the risk of fractures.

See the table Drugs Used to Treat Osteoporosis.

Treatment of fractures: Treatment of a fracture due to osteoporosis depends on the location of the fracture. Treatments include splints, casts, and surgery (such as insertion of pins or replacement of a joint). If a person has severe pain due to a collapsed vertebra, vertebroplasty or kyphoplasty may be done. In these procedures, a needle is used to inject plastic cement into a collapsed vertebra.

Outlook

Treating osteoporosis can help prevent fractures. However, treatment does not reverse the changes in appearance (such as loss of height) due to previous fractures.

Treatment of osteoporosis is not always effective. In up to 1 out of 6 people who take drugs for osteoporosis, bone density continues to decrease. Doctors periodically check to determine how well a drug is working. Several months after the start of treatment, blood and urine tests may be repeated to determine whether less bone is being broken down. DEXA scanning or another test to measure bone density may be repeated after 1 to 2 years. If bone density is continuing to decrease, doctors may recommend that the person take a higher dose of the drug, a different drug, or an additional drug. Changing treatment may be effective.