Osteoporosis is a condition in which a decrease in the density of bones weakens the bones, making fractures likely.
Bones contain minerals, including calcium and phosphorus, which make them hard and dense. To maintain bone density, the body requires an adequate supply of calcium and other minerals and must produce the proper amounts of several hormones, such as parathyroid hormone, growth hormone, calcitonin, estrogen, and testosterone. An adequate supply of vitamin D is also needed to absorb calcium from food and incorporate it into bones. Vitamin D is absorbed from the diet and also manufactured in the skin using sunlight (see Vitamins: Vitamin D).
So that bones can adjust to the changing demands placed on them, they are continuously broken down and reformed, or remodeled (see Biology of the Musculoskeletal System: Bones). In this process, small areas of bone tissue are removed and new bone tissue is deposited. This process is continuous. Remodeling affects the shape and density of the bones. In youth, the bones grow in width and length as the body grows. In later life, bones may sometimes enlarge in width but do not continue to grow longer.
Because more bone is formed than is broken down in the young adult years, bones progressively increase in density until about age 30, when they are at their strongest. After that, as breakdown exceeds formation, bones slowly decrease in density. If the body is unable to maintain an adequate amount of bone formation, bones continue to lose density and may become increasingly fragile, eventually resulting in osteoporosis.
About 8 million women and 2 million men in the United States have osteoporosis. There are two main types of osteoporosis: primary osteoporosis, which occurs spontaneously, and secondary osteoporosis, which is caused by another disorder or drug.
More than 95% of osteoporosis in women and probably about 80% in men is primary. Most cases occur in postmenopausal women and in older men.
A major cause of osteoporosis is a lack of estrogen, particularly the rapid decrease that occurs at menopause. Most men over 50 have higher estrogen levels than postmenopausal women, but these levels also decline with aging, and low estrogen levels are associated with osteoporosis in both men and women. Estrogen deficiency increases bone breakdown and results in rapid bone loss. In men, low levels of male sex hormones also contribute to osteoporosis. Bone loss is even greater if calcium intake or vitamin D levels are low. Low vitamin D levels result in calcium deficiency and increased activity of the parathyroid glands (secreting parathyroid hormone), which can also stimulate bone breakdown. For unknown reasons, bone production also decreases.
A number of other factors increase the risk of bone loss and the development of osteoporosis in women. These risk factors are probably also important in men. People who have had one fracture in which osteoporosis had been a factor are at much higher risk of having more such fractures.
Examples of disorders that may cause secondary osteoporosis are chronic kidney disease and hormonal disorders (especially Cushing disease, hyperparathyroidism, hyperthyroidism, hypogonadism, high levels of prolactin, and diabetes mellitus). Examples of drugs that may cause secondary osteoporosis are corticosteroids, thyroid hormones, certain chemotherapy drugs, and anticonvulsants. Excessive alcohol or caffeine consumption and cigarette smoking may worsen preexisting osteoporosis but are unlikely to cause it.
Idiopathic osteoporosis is a rare type of osteoporosis. The word idiopathic simply means that the cause is unknown. This type of osteoporosis occurs in premenopausal women, in men under age 50, and in children and adolescents who have normal hormone levels, normal vitamin D levels, and no obvious reason to have weak bones.
At first, osteoporosis causes no symptoms because bone density loss occurs very gradually. Some people never develop symptoms.
Eventually, however, bone density may decrease enough for bones to collapse or fracture, causing severe sudden pain or gradually developing aching bone pain and deformities. In long bones, such as the bones of the arms and legs, the fracture usually occurs at the ends of the bones rather than in the middle. The bones of the spinal column (vertebrae) are particularly at risk of fracture due to osteoporosis. The fracture usually occurs in the middle to lower back.
Vertebral compression fractures (fractures of spinal vertebrae) may occur in people who have any type of osteoporosis. The weakened vertebrae may collapse spontaneously or after a slight injury. Most of these vertebral compression fractures do not cause pain. However, pain can develop, usually starting suddenly, staying in a particular area of the back, and worsening when a person stands or walks. The area may be tender. Usually the pain and tenderness begin to go away gradually after 1 week. However, lingering pain may last for months or be constant. If several vertebrae break, an abnormal curvature of the spine (a dowager's hump) may develop, causing muscle strain and soreness as well as deformity.
Bones in other parts of the body may fracture, often because of a relatively minor strain or fall. One of the most serious fractures is a hip fracture, a major cause of disability and loss of independence in older people (see Fractures: Hip Fractures). Common wrist fractures (see Fractures: Wrist Fractures) occur often, especially in people with postmenopausal osteoporosis. In addition, fractures tend to heal slowly in people who have osteoporosis.
A doctor may suspect osteoporosis in the following people:
Bone density testing can be used to detect or confirm suspected osteoporosis, even before a fracture occurs. A number of rapid screening techniques are available to measure density at the wrist or the heel. The most useful test, however, is dual-energy x-ray absorptiometry (DXA), which measures bone density at the sites at which major fractures are likely to occur: the spine and hip. This test is painless, involves very little radiation, and can be done in about 5 to 15 minutes. It may be useful for monitoring the response to treatment as well as for making the diagnosis.
Blood tests may be done to measure calcium and vitamin D levels. Further testing may be needed to rule out treatable conditions that might lead to osteoporosis. If such a condition is found, the diagnosis is secondary osteoporosis.
Prevention and Treatment
Prevention is generally more successful than treatment because it is easier to prevent loss of bone density than to restore density once it has been lost. Prevention involves managing risk factors (for example, quitting smoking and avoiding excess alcohol and caffeine use), maintaining or increasing bone density by consuming adequate amounts of calcium and vitamin D, engaging in weight-bearing exercise, and, for some people, taking certain drugs. Treatment also involves ensuring adequate intake of calcium and vitamin D and engaging in weight-bearing exercises. All people being treated need to take drugs.
Certain measures can help prevent fractures. Many older people are at risk of falls because of poor coordination, poor vision, muscle weakness, confusion, and use of drugs that cause light-headedness when people stand or cause confusion. Modifying the home environment for safety (see Falls: Prevention) and working with a physical therapist to develop an exercise program can help. Strengthening exercises may help improve balance.
Diet and exercise:
Consuming an adequate amount of nutrients, particularly calcium and vitamin D, is helpful, especially before maximum bone density is reached (around age 30) but also after this time. About 1200 to 1500 milligrams of calcium and 600 to 800 units of vitamin D daily are recommended, although slightly lower amounts may be sufficient for younger people and some people need more. Sometimes doctors check the level of vitamin D in the blood to determine how much supplemental vitamin D should be taken. Drinking two 8-ounce glasses of vitamin D-fortified milk, eating a balanced diet, and taking a vitamin D supplement are important, but many women may also need to take a calcium supplement. Many calcium preparations are available, and some include supplemental vitamin D. Supplements should be taken as calcium citrate if people take a proton pump inhibitor such as omeprazole (which are used to reduce stomach acid production) or have had gastric bypass surgery.
Weight-bearing exercise, such as walking and stair-climbing, increases bone density. Exercises that do not involve weight bearing, such as swimming, do not increase bone density. Most experts recommend about 30 minutes of weight-bearing exercise daily. Exercise is also important to improve balance, which can help to prevent a fracture that may occur from falling. Curiously, in premenopausal women, high levels of exercise, such as those maintained by athletes, can actually cause a small reduction in bone density because such exercise suppresses the production of estrogen by the ovaries.
Most of the same drugs are used for prevention and treatment.
Drugs called bisphosphonates (alendronate, risedronate, ibandronate, and zoledronic acid) are useful in preventing and treating all types of osteoporosis and are usually the first drugs used. Bisphosphonates have been shown to increase bone density in the spine and hips and reduce the risk of fractures. Alendronate and risedronate can be taken by mouth (orally). Zoledronic acid can be given by vein (intravenously). Ibandronate can be taken orally or intravenously.
An oral bisphosphonate must be swallowed with a full glass of water (8 ounces) after arising for the day. No other food, drink, or drug should be consumed for the next 30 minutes because food in the stomach may decrease the absorption of the drug. Because oral bisphosphonates can irritate the lining of the esophagus, the person must not lie down for at least 30 minutes (60 minutes for ibandronate) after taking a dose and then must not lie down until after something has been eaten. Certain people, including those who have difficulty swallowing, gastrointestinal symptoms (for example, heartburn or nausea), and certain disorders of the esophagus or stomach, should not take the bisphosphonates orally. These people can be given ibandronate or zoledronic acid intravenously. In addition, the following people should not take bisphosphonates:
At this time, doctors do not know how long people should take bisphosphonates. Most people need to take these drugs for 3 to 5 years, and some people may need to take them for up to 10 years. The determination of how long taking the drugs is likely to be helpful is made by the doctor and is based on a person's medical condition and risk factors for fracture. After stopping, doctors usually do periodic tests to determine whether bone mass is decreasing. If bone mass is decreasing, treatment with a bisphosphonate or another drug may be restarted.
Osteonecrosis of the jaw (see Osteonecrosis: Osteonecrosis of the Jaw) is a rare condition that has occurred in some people who take bisphosphonates. In this condition, the jaw becomes damaged and infected. People who have had extensive dental work or injury, take bisphosphonates intravenously, who have cancer, or a combination are at highest risk. However, it is not truly clear whether bisphosphonates cause osteonecrosis of the jaw and, if they do, which particular drugs are most likely to cause it. There is also no evidence that stopping bisphosphonates before having dental work helps.
Long-term use of bisphosphonates may increase the risk of developing unusual fractures of the thigh bone (femur). However, bisphosphonates, when used as prescribed, prevent more fractures than they may cause.
Calcitonin, which inhibits the breakdown of bone, is another drug used for treatment but not frequently. Calcitonin seems to be less effective in reducing fracture risk than other available drugs but it can help relieve pain caused by vertebral fractures. Calcitonin is usually taken by nasal spray. Its use can decrease blood levels of calcium, so these levels must be monitored.
Hormonal therapy (for example, with estrogen) helps maintain bone density in women and can be used for prevention or treatment. This therapy is most effective when started within 4 to 6 years after menopause, but starting it later can still slow bone loss and reduce the risk of fractures. However, because the risks of hormonal therapy exceed its benefits for most women, hormonal therapy is usually not the treatment option used. Decisions about using estrogen replacement therapy after menopause are complex (see Menopause: Hormone therapy).
Raloxifene is an estrogen-like drug that may be less effective than estrogen in preventing and treating bone loss, but it does not have some of estrogen‘s negative side effects. Raloxifene is used in people who cannot or prefer not to take bisphosphonates. Raloxifene can reduce the risk of spine fractures and may reduce the risk of breast cancer.
Men do not benefit from estrogen but may benefit from testosterone replacement therapy if their testosterone level is low.
A synthetic form of parathyroid hormone called teriparatide can be injected daily in small amounts. Teriparatide increases the formation of new bone, increases bone density, and decreases the likelihood of fractures. This therapy is used in some people who
Treatment of fractures:
Fractures resulting from osteoporosis must be treated. For hip fractures, usually part or all of the hip is replaced surgically (see Fractures: Hip Fractures). Surgery may be needed for a wrist fracture, or the wrist may need to be placed in a cast. Supportive back braces are used temporarily for people with painful vertebral compression fractures. Calcitonin can decrease the pain caused by vertebral fractures.
A collapsed vertebra can be repaired by a procedure called vertebroplasty. In this procedure, which takes about an hour for each vertebra, a material called methyl methacrylate (MMA)—an acrylic bone cement—is injected into the collapsed vertebra, helping to relieve pain and reduce deformity. Kyphoplasty is a similar procedure, in which an orthopedic balloon is used to expand the vertebra back to its normal shape before the injection of the MMA. With vertebroplasty and kyphoplasty, deformity may be reduced in the MMA-injected bone, but the risk of fractures in adjacent bones in the spine or ribs does not decrease and may even increase. Other risks may include rib fractures, cement leakage, and possibly heart or lung problems. When these procedures should be recommended has not been determined.
Last full review/revision February 2013 by Marcy B. Bolster, MD