Osteoporosis

Bone remodeling occurs because bone is made primarily of calcium and phosphorous. Calcium is critically involved in muscle contraction, nerve impulse transmission, and many metabolic activities within cells. To remain healthy, the body must keep the level of free calcium ions (Ca²⁺) in the blood within a very narrow concentration range. Besides providing a framework for the body, bone acts as a calcium “bank.” When excess calcium is present in the blood, osteoblasts deposit it into bones where it is stored. When too little calcium is present, osteoblasts dissolve calcium from bones and move it into the blood. This process is controlled mainly by parathyroid hormone (PTH) secreted by the parathyroid glands in the neck. As people age, various conditions cause them to take more calcium out of the “bone bank” than they deposit, and osteoporosis eventually develops. A person's peak bone mass and the rate at which they lose it in later life affect their risk of developing osteoporosis; the higher the peak bone mass at age 30, the lower the risk of osteoporosis later on.

Doctors divide osteoporosis into three categories, or types. Types 1 and 2 are considered primary because they are not caused by other diseases or conditions. Type 3 osteoporosis is sometimes called secondary osteoporosis because it results from taking certain drugs or having other diseases.

According to the National Osteoporosis Foundation (NOF), as of 2011 about 10 million people (8 million women and 2 million men) in the United States have osteoporosis, and another 34 million adults have low bone density, a condition called osteopenia. Osteopenia can develop into osteoporosis if it is not treated. Osteoporosis is responsible for more than 1.5 million fractures annually in the United States, including 300,000 hip fractures, 700,000 vertebral fractures, 200,000 wrist fractures, and more than 300,000 fractures in other parts of the body. The costs of treating osteoporosis and the fractures that it causes come to more than US$19 billion each year. An osteoporosis-related fracture occurs in one in two women and one in eight men over the age of 50.

Although osteoporosis is often thought of as a woman's disease, it affects men, too. Men who take certain medications, particularly cortisone and other steroid drugs, have the same risk of developing osteoporosis as women who take these medications. Each year, 80,000 American men with osteoporosis have a hip fracture, and one-third of them die within a year.

Worldwide, osteoporosis is estimated to affect one in three women and one in 12 men over the age of 50. It is the most common metabolic bone disease in the world.

Osteoporosis in children is very unusual. There is a rare condition called juvenile idiopathic osteoporosis. About 60 cases have been reported worldwide. Idiopathic means that the cause of the condition is unknown.

Risk factors

There are two basic categories of risk factors for osteoporosis. Some of these risk factors can be changed, while others cannot be altered. Risk factors that cannot be changed include:

Risk factors for osteoporosis that people can change include:

Certain diseases also increase a person's risk of developing osteoporosis:

The basic cause of osteoporosis is that the loss of bone tissue occurs faster than the production of replacement bone. The increased rate of bone loss can be particularly critical if the person had a low or inadequate peak bone mass to begin with. A low peak bone mass can result from malnutrition in childhood; inadequate intake of calcium or vitamin D (vitamin D is necessary for the body to make use of calcium in the diet); an eating disorder in adolescence, when the body's need for calcium is at its height; or not getting enough exercise.

Osteoporosis results from a complex interaction between genetic and environmental factors throughout life. Evidence suggests that peak bone mass is inherited, but current genetic markers are able to explain only a small proportion of the variation in individual bone mass or fracture risk. As of 2011, no specific mode of inheritance has been identified. Heritability of bone mass has been estimated to account for 60%–90% of its variance. Studies have shown reduced bone mass in daughters of osteoporotic women when compared with controls, in men and women who have first-degree relatives (parents, siblings) with osteoporosis, and in perimenopausal women who have a family history of hip fracture. Body weight in infancy may be a determinant of adult bone mass.

Many candidate genes exist for osteoporosis; however, relatively few have been studied. The first candidate gene to be identified was the vitamin D receptor (VDR) gene, and studies are ongoing as to how much this gene accounts for variance in bone mass. The response of bone mass to dietary supplementation with vitamin D and calcium is known to be dependent, in part, on VDR polymorphisms. Other genes may aid in establishing who would benefit from treatments such as drug therapy or exercise. Associations between bone mass and polymorphisms have also been found in the estrogen receptor gene, the interleukin-6 genes, the transforming growth factor beta, and a binding site of the collagen type I alpha1 (COLIA1) gene.

The risk of osteoporosis is greatly determined by peak bone mass, and any gene linked to fractures in the elderly may possibly be associated with low bone mass in children as well. Some scientists think that environmental influences during early life interact with the genome to establish the functional level of a variety of metabolic processes involved in skeletal growth.

Osteoporosis can proceed for a long time without any noticeable symptoms. Some older adults simply notice that their height is shrinking. This loss of height is caused by compression of the bones in the spinal column. Sometimes the vertebrae fracture as they come closer together; this type of injury is called a compression fracture.

Over many years, a sequence of spinal compression fractures may cause kyphosis, the bent-over posture known as dowager's or widow's hump. These fractures rarely require surgery, and they can range from causing minor discomfort to severe painful episodes of backache. In either case, pain generally subsides gradually over one to two months.

Another common symptom of osteoporosis is a fragility fracture. Fragility fractures occur when a person falls from a standing position or a low height and breaks a bone that would not break in a person with healthy bone. The most common locations of fragility fractures in people with osteoporosis are the wrists, the hips, and the vertebrae in the spine. The individual may experience vertebral pain in various ways; some describe it as sharp while others describe it as dull or nagging. In some cases the pain gets worse when walking or moving around.

Since osteoporosis can develop undetected for decades until a fracture occurs, early diagnosis is important. Osteoporosis is most likely to be diagnosed following a fragility fracture. The doctor will take a careful history of the patient's risk factors, including a possible family history of easily broken bones as well as a medication history and questions about such lifestyle factors as exercise, diet, smoking, and drinking.

The physical examination includes measurement of the patient's height, evaluation of possible loss of height, and assessment for evidence of kyphosis.

The doctor may order a blood test to rule out a thyroid disorder or to check the levels of sex hormones in the patient's blood.

A bone mineral density test (BMD) is the only way to diagnose osteoporosis and determine risk for future fracture. The painless, noninvasive test measures bone density and helps determine whether medication is needed to help maintain bone mass, prevent further bone loss, and reduce fracture risk. To take this test, the patient lies on an examination table while two x-ray beams of different intensities are aimed at the bones. The result is called a T-score. It is calculated by comparing the patient's bone mineral density to that of a healthy 30-year-old of the same sex and race. A T-score of —1.0 or higher is normal; a score between —1.0 and —2.5 indicates osteopenia; a score below —2.5 indicates osteoporosis.

Several different machines measure bone density. Central machines, such as the dual-energy x-ray absorptiometry (DXA or DEXA) and quantitative computed tomography (QCT), measure density in the hip, spine, and total body. Peripheral machines, such as radiographic absorptiometry (RA), peripheral dualenergy x-ray absorptiometry (pDXA), and peripheral quantitative computed tomography (pQCT), measure density in the finger, wrist, kneecap, shin bone, and heel.

A physician may be able to observe osteoporotic bone in a routine spinal x-ray, however, BMD tests are more accurate and can measure small percentages of lost bone density. In an x-ray, osteoporotic bone appears less dense and the image is less distinct, suggesting weaker bone.

As of 2011, the United States Preventive Services Task Force recommended using DEXA to screen all women 65 years and older and women 60–64 years of age who have increased fracture risk. Some physicians also recommend bone density testing at menopause at whatever age it occurs to begin preventive treatment, if necessary. The major risk factors are low body weight, low calcium intake, poor health, and a family history of osteoporosis.

Some healthcare organizations recommend screening all men 70 years and older, as well as men with one of the following risk factors: bone fracture, poor health, or low testosterone levels.

Medications are an important part of treatment for osteoporosis. Various drugs have been shown to be effective in preventing or slowing bone loss and increasing bone mass. These include:

Recommended lifestyle changes that can reduce the rate of bone loss include regular exercise, particularly weight-bearing forms of exercise like walking, dancing, treadmill exercises, and jumping. Other measures include quitting smoking, taking supplemental vitamin D and calcium, and watching one's alcohol intake.

NUTRITIONAL THERAPY. A healthful diet low in fats, salt, sugar, and nutritionally inferior processed foods, and containing whole grains, fruits and vegetables, nuts and seeds, and calcium-rich foods (particularly dairy products, dark green leafy vegetables, sardines, salmon, and almonds), along with nutritional supplements (such as calcium, magnesium, and vitamin D) are important components of nutritional approaches to treating this disease. Calcium found in dairy products is well absorbed by the body making them a valuable source of calcium.

In addition, women should avoid foods that may accelerate bone loss. They should cut down on caffei-nated beverages if their intake is excessive (more than five cups of coffee a day). Some studies have shown that high amounts of caffeine can decrease calcium absorption. Research is mixed on the impact of soda consumption on bone health. Some studies have suggested that the phosphoric acid found in many sodas can negatively affect bone health, while others have shown that it has no effect. What most experts do agree on is that caffeinated beverages and sodas should be consumed in moderation for good health.

The prognosis for osteoporosis depends on its type and cause; the patient's age, sex, and ethnicity; the presence of other diseases or disorders; and the patient's willingness to follow the doctor's recommendations about medications and lifestyle changes.

People cannot change such risk factors for osteoporosis as age, sex, and race, but they can eat properly, exercise regularly, and ask their doctor about vitamin D and calcium supplements. Male and female adolescents should participate in sports and get adequate calcium in the diet in order to build up a high peak bone mass before midlife. Women who have not yet gone through menopause should get at least 1,000 milligrams (mg) of elemental calcium and a minimum of 800 international units (IU) of vitamin D every day; women who have completed menopause, anyone who must take steroid medications, and all men and women over age 65 should aim for 1,500 mg of elemental calcium and at least 800 IU of vitamin D daily.

Other recommendations for lowering the risk of osteoporosis in older adults include:

Older adults should try to reduce their risk of falls whether or not they have osteoporosis. There are balance and strength exercises that older adults can practice at home. In addition, such safety measures as wearing properly fitted shoes with nonslip soles, checking one's house for loose rugs, poor lighting, and other hazards, installing grab bars in shower stalls, and keeping a cordless phone within easy reach in case of an accident are all good forms of fall prevention.

Calcium and vitamin D are both essential to building and maintaining strong bones. Dairy products are a good source of these nutrients. Calcium supplements are recommended for many women who have difficulty getting enough calcium in their diet. Recommended dietary allowances (RDAs) and lists of foods that are high in calcium and vitamin D can be found in their individual entries. Fluoride also is needed to develop healthy bones and teeth.

Although good bone health is important for everyone, it is especially important for athletes and individuals who engage in recreational fitness activities. Weak bones can increase the likelihood of serious injury during participation in sports and fitness activities for athletes of all ages and skill levels.

Elite athletes can be at increased risk of osteoporosis. Extreme training regimens and diets that lack the required amounts of calcium and vitamin D can be problematic. It is especially important for elite athletes to have strong, healthy bones because of the repeated pressures and strains often put on them during training and competition.

Repetitive stress on the bones, such as running during marathons or track and field events, and repeated jumping during basketball, figure skating, or ballet can lead to fractures in athletes who do not have good bone health. Many sports involve sudden strains on bones, such as during gymnastics, wrestling, and baseball, that can lead to fractures and breaks if bones are brittle. These kinds of injuries, while painful and difficult for everyone, can be especially problematic for elite and professional athletes as serious injuries can lead to missing seasons, forgoing important competitions, and loss of income.

Female athletes are at special risk of the female athlete triad, which is the combination of disordered eating, amenorrhea (cessation of a normal menstrual period), and osteoporosis. This triad is often caused by eating disorders including anorexia and bulimia. Athletes are at increased risk for developing eating disorders because of the focus on body shape and the perception that losing a few more pounds could provide a competitive edge.

Young people with the eating disorder anorexia nervosa are at especially high risk of developing osteoporosis later in life because they have poor, unbalanced diets. The menstrual cycle in girls with anorexia is often delayed in starting or if it has started, stops. In addition, people with anorexia almost never get enough calcium to build strong bones during adolescence and they make unusually larger amounts of cortisol, a corticosteroid made by the adrenal gland that causes bone loss. Although the effect of this eating disorder on bones will not be seen until the individual is older, failure to build strong, dense bones during the teen years substantially increases the risk of osteoporosis later.

The bone health of young athletes is especially important because good bone health is required for normal growth and development. Children and adolescents who do not get enough calcium and vitamin D are at an increased risk for growth problems as well as bone fractures and breaks. Young female athletes are especially at risk for the female athlete triad. Parents of young athletes of both genders should be alert for signs of disordered eating, and work closely with their children to ensure that their children are eating a healthy, well-balanced diet.

Regular exercise is important to good health and can improve quality of life and bone health well into the later senior years. However, older athletes need to take precautions when exercising to help protect their bones. Because older people are more likely to have osteoporosis, and because bones generally weaken during the later years, older athletes are at increased risk for bone fractures and breaks. Working with a doctor and nutritionist is important to ensure a balanced diet that includes enough calcium and vitamin D. Participating in sports such as walking and low-impact aerobics that have a reduced likelihood of causing sudden impacts to the bones is a good idea. Strength training can improve balance and help reduce the risk of falls that can reduce the risk of broken hips and wrists. With a few precautions, older athletes are often able to continue to engage in the sports and fitness activities they enjoy well into their senior years.

See also Bone health .