Osteoporosis

Osteoporosis (os-te-o-po-RO-sis) is a disorder in which there is loss of bone density, which increases the likelihood of fracture.

Bone consists of two layers: a compact outer layer, called cortical bone, and a porous inner layer, called spongy (or cancellous) bone. Osteoporosis weakens mostly bones with a large percentage of spongy bone. These include the vertebrae (bones of the spine), the hips, and the wrists. Bones of this kind are more fragile and are especially prone to fracture when affected by osteoporosis.

Osteoporosis develops gradually over time, although rates vary in different individuals. It results from an imbalance in the normal process in which bone is constantly being broken down and replaced by new bone. In osteoporosis, the rate at which bone tissue is lost exceeds the rate at which it is replaced. This imbalance results in an overall loss of bone.

Prevalence of Osteoporosis

No one can say how many people have osteoporosis, because it develops gradually and merges with the natural process of aging. However, it is known that women are much more likely to develop the disorder than men, and that people of European ancestry have a higher incidence of osteoporosis than people of African ancestry.

Often, a person can have osteoporosis but not be aware of it until she fractures a bone. Typically, this happens in a fall that would not have caused the fracture to occur in a young adult. It has been estimated that in the United States osteoporosis is responsible for more than 1.2 million bone fractures each year. Among women, surveys indicate that at least 10 percent of those over age 50 have bone loss severe enough to increase the risk of fractures of the spine, hip, or long bones.

Types and Causes of Osteoporosis

Osteoporosis is classified as primary or secondary, depending on whether there is some other condition or abnormality causing the bone loss.

Primary osteoporosis

Primary osteoporosis is the most common form of the disorder. It has been divided further into age-related osteoporosis, postmenopausal osteoporosis, and idiopathic (of unknown cause) juvenile osteoporosis. Age-related (or senile) osteoporosis occurs mostly in elderly people whose bones have become significantly thinner owing to their advanced age. Postmenopausal osteoporosis results from the acceleration of bone loss in women after they have reached menopause ^* , when their ovaries have stopped producing estrogen, a hormone that helps maintain bone mass.

The amount of bone mass a person has as a young adult when the skeleton is mature is believed to be related to the likelihood of developing osteoporosis after middle life. It is believed that the generally greater incidence ^* of osteoporosis in women than in men, and in people of European background than in those of African origin, is due largely to their lower skeletal density as young adults. Moreover, the density of bone in a person's skeleton in young adulthood is partly determined by his or her genes ^* (inherited), and people with lighter skeletons who develop osteoporosis in later life are likely to have relatives with the same condition.

Juvenile osteoporosis is rare and occurs in boys and girls before they reach their teens. It may last 2 to 4 years until normal bone growth resumes. Another uncommon form occasionally develops in young adults.

Secondary osteoporosis

A condition is said to be "secondary" when it is caused by something else not functioning correctly. Secondary osteoporosis may have several causes. Immobility, as in someone with a paralytic disease, can cause the bones to thin and become brittle. This effect also has been observed in astronauts who have undergone prolonged periods of weightlessness in space. (It is difficult to get proper exercise when there is no gravity to work against.)

Additional causes of secondary osteoporosis include hormonal diseases, such as hyperthyroidism, and estrogen loss caused by failure or removal of the ovaries ^* . Nutritional disorders such as anorexia nervosa can also lead to osteoporosis. Smoking and heavy consumption of alcoholic beverages are thought to be strong contributing factors in some cases of osteoporosis.

Signs and Symptoms

Osteoporosis does not always produce obvious symptoms. That is why an older person may first learn of his or her condition after breaking a bone in a fall. An x-ray then reveals the decreased bone density.

It has been estimated that 70 percent of fractures in people age 45 and older can be attributed to osteoporosis. About one third of women older than age 65 will have fractures of the vertebrae. The ratio of women to men experiencing spinal fractures is about 8 to 1. By the time people reach very advanced age, one third of women and one sixth of men will have broken a bone in the hip. Another common site of fracture is the forearm bone (radius) just above the wrist.

The thinning vertebrae in a person with osteoporosis may collapse spontaneously. Called compression fractures, these breaks can cause severe pain, usually in the mid or lower back. Chronic, or long-lasting, pain may develop after several such fractures have occurred. The person may gradually lose inches of height, and the upper back often curves forward. These signs and symptoms typically develop in women within 20 years after menopause if osteoporosis is not treated.

Diagnosing Osteoporosis

A diagnosis of osteoporosis is usually made by noting the person's physical appearance in general and the spine in particular. X-rays can reveal that the bones are less dense than normal. Special imaging techniques, including photon densitometry (FO-ton den-si-TOM-e-tree), are also used to detect osteoporosis.

In some instances, a blood test and bone biopsy (removal of a tiny sample of bone for examination) may be used to rule out the possibility of osteomalacia (OS-te-o-ma-LAY-she-a), a closely related condition in adults that results from a lack of vitamin D.

Treatment Options

If osteoporosis is not treated, the loss of bone density may continue. The risk of fractures will increase correspondingly as the person ages. Treatment is aimed primarily at stopping the bone loss.

Medications

Calcium supplements in tablet form at recommended dosages are safe, inexpensive, and effective. Still more effective is treatment with the hormone estrogen, but this can have harmful side effects. Doctors may or may not prescribe estrogens, depending largely on other health considerations in individual patients. Other drugs such as calcitonin can prevent bone loss and may be given to women who do not take estrogen.

False-color x-ray of upper part of femur (thigh bone) with osteoporosis shown in yellow-orange. Fractures are likelier when this amount of osteoporosis occurs because it decreases bone density, which increases brittleness.

Alfred Pasieka/Science Photo Library, Photo Researchers, Inc.

Certain drugs taken to treat other conditions may have the additional effect of causing bone loss. The use of such medications may have to be curtailed or adjusted for people who have osteoporosis. Cortisone, thyroid hormone, and diuretics (used for various disorders to increase the flow of urine) are examples of drugs that can cause loss of bone density.

Men who develop osteoporosis usually are not given hormone treatment but take calcium supplements and can be given some of the newer drugs available.

Lifestyle

General measures that can be taken to slow further loss of bone include undertaking a regular program of exercise (induding long walks or some equivalent activity), quitting smoking, and drinking alcoholic beverages only in moderation. Good eating habits are important, and a balanced diet should include adequate calcium, vitamins, and other nutrients. Elderly people need to take precautionary measures to avoid falls.

Pain Relief

Standard pain-relieving drugs, such as aspirin, and heat applications can be used for back pain. Posture training and special exercises for the stomach and back muscles can have long-term benefits in reducing pain and discomfort. Occasionally a back brace may be necessary to provide support.

Early Prevention

The best time to start taking steps to prevent osteoporosis is during the childhood and teen years. This is particularly so for young women with lightweight skeletons and small bones and who have close relatives with osteoporosis. As in older people, getting plenty of regular exercise is important, as is calcium in the diet. It is estimated that more than 70 percent of children and teenagers fail to consume adequate amounts of calcium in their diets. Foods rich in calcium include milk and other dairy products, green leafy vegetables, citrus fruits, fish such as sardines and mackerel, and shellfish. The aim is to achieve full, normal bone density in the skeleton at maturity.

Lifestyle choices such as not smoking and limiting alcohol use are important. Also to be avoided are fad diets that promise rapid weight loss. While exercise, particularly supervised weight training, is important in the prevention of osteoporosis, excessive exercise in teenage girls and young women can have the opposite effect. Extreme amounts of exercise (especially if it is combined with dieting and weight loss) can cause the stopping of menstrual periods and decreased estrogen levels in the body. Significant bone loss can be a result.