Table of Contents
Osteoporosis is a chronic disorder in which the mass of bones decreases and their internal structure degenerates to the point where bones become fragile and break easily.
Bone is living material. It is constantly broken down by cells called osteoclasts and built up again by cells called osteoblasts. This process is called bone remodeling, and it continues throughout an individual’s life. Normally, more bone is built up than is broken down from birth through adolescence. In the late teens or early twenties, people reach their peak bone mass—the most bone that they will ever have. For twenty or so years, bone gain and bone loss remain approximately balanced in healthy people with good nutrition. However, when women enter menopause, usually in their mid to late forties, for the first 5to 7 years bone loss occurs at a rate of 1–5% a year. Men
tend to lose less bone, and the loss often begins later in life. Osteoporosis occurs when bone loss continues and bones become so thin and their internal structure is so damaged that they break easily.
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 (Ca 2+) 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 (which literally means porous bones) eventually develops. Osteoporosis is a silent disorder. It usually
shows no symptoms until bones become so weak that they fracture from a seemingly minor bump of fall. All bones in the body may be affected by osteoporosis, but spinal vertebrae, the hip, and the wrist and forearm are the bones most often broken.
The National Osteoporosis Foundation estimates that 10 million people in the United States over age 55 have osteoporosis, and another 34 million have lost enough bone mass to put them at high risk for developing the disorder. The National Institutes of Health estimate that 25 million people in the United States have osteoporosis. Since people rarely seek treatment until they have a bone fracture, accurate estimates are difficult to obtain. However, about 1.5 million fractures are attributed to osteoporosis in the United States each year. Internationally, in Europe 1 of every 8 people over age 50 will have a spinal fracture, suggesting a high rate of osteoporosis.
Osteoporosis is a disorder of older individuals. It rarely develops before age 50. and the likelihood of developing it increases steadily with age. Eighty percent of the people who have osteoporosis are women, but there is a fair amount of variation among the rate in women of different ethnic groups. White women, especially those of northern European ancestry, are at highest risk of developing osteoporosis. Their rate is twice as high as Hispanic women and four times as high as black women. White men also are most likely to be affected, but the differences in the rate of osteoporosis among men of different races and ethnicities is smaller than among women.
Although the immediate cause of osteoporosis is loss of bone, there are many risk factors that increase the change of developing this condition. Age, race, gender, and heredity play a role in the development of osteoporosis, but other the risk factors are related to lifestyle. These include:
- cigarette smoking. Smoking causes the liver to destroy estrogen at a faster than normal rate .
- heavy alcohol consumption. Alcohol can interfere with calcium absorption.
- lack of exercise. Weight bearing exercises help increase bone mass.
- too much strenuous exercise in women. Extreme exercise causes menstrual cycles to stop (amenorrhea), reducing estrogen levels.
- Poor diet. Vitamin D and calcium are both necessary to build strong bones.
Medical conditions and treatments can also cause osteoporosis. These include:
- conditions that cause low testosterone levels in men (e.g. hypogonadism)
- cancer or treatment with certain chemotherapy drugs (e.g. cyclosporine A).
- early hysterectomy or removal of the ovaries. This reduces the level of estrogen in the body.
- use of anticonvulsant drugs (e.g. phenytoin, carba-mazepin). These cause vitamin D deficiency and reduce the amount of calcium absorbed from the intestine.
- long-term use of corticosteroids drugs (e.g. cortisone, prendisone) to treat conditions such as systemic lupus erythematosus (SLE) or rheumatoid arthritis. These drugs directly inhibit bone formation.
- Certain hormonal disorders such as Cushing syndrome where the body makes too many corticosteroids
- spinal cord injury that results in paralysis or any other medical condition that severely limits the individual’s physical activity
Osteoporosis is a disorder that shows few obvious symptoms. Elderly individuals may begin to lose height and develop a curved upper back and what is sometimes called a dowagers hump. For most people, signs of osteoporosis only become apparent when they either fracture a bone or have a bone mineral density (BMD) test done.
Diagnosis begins with a medical history to determine whether what risk factors the individual has. The physician may order blood and urine tests to rule out other disorders. The definitive test for osteoporosis is a bone mineral density (BMD) test. The most commonly used BMD is called a dual-energy x-ray absorptiometry (DXA)test. This test measures the density of bone in the hip and spine. It is similar to an x ray, only with less exposure to radiation, and it is painless. Results are given as a T-score, with negative numbers indicating low bone mass. Occasionally the physician may order a bone scan. A bone scan checks for bone inflammation, fractures, bone cancer, and other abnormalities, but it does not measure bone density.
Osteoporosis cannot be cured but it can be treated with exercise (see Therapy), diet, and sometimes with medication. There are several types of prescription medications approved by the United States Food and Drug Administration for the treatment of osteoporosis.
- Antiresorptive medications slow or prevent bone from being broken down. These include alendronate sodium (Fosamax), ibandronate sodium (Boniva), etidronate (Didronel), and risedronate sodium (Actonel). If drug therapy is used, these medication are often the first choice.
- In women, estrogen therapy and hormone replacement therapy drugs increase the level of estrogen in the body and improve bone health. Because of side effects such as the increase in breast cancer, heart attacks, and stroke, these drugs are used less frequently. Most often they are used to treat other symptoms of menopause rather than specifically to treat osteoporosis.
- Selective estrogen receptor modulators (SERMs) such as raloxifene (Evista). These drugs are being developed to replace estrogen and hormone therapy drugs. They act on estrogen receptors in bone in a way that prevents the bone from being broken down.
- Parathyroid hormone stimulates the formation of new bone by activating more new osteoblasts. It is marketed as teriparatide (Fortéo)
- Calcitonin (Miacalcin, Calcimar, Cibacalcin) is a hormone that slows bone breakdown by inhibiting osteoclast activity.
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.
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.
Physical therapy involving weight-bearing exercises an help individuals of any age, even those who are frail or have chronic illnesses slow bone loss and regain muscle mass. Physical therapy exercises that emphasize improving strength, flexibility, coordination, and balance also decrease the risk of falls and fractures in individuals who have osteoporosis.
Osteoporosis cannot be cured but preventive behaviors and treatment can slow its progression. Falls that result in hip and spine fractures present the greatest risk of complications. Almost one-fourth of people over age 50 who have hip fractures die within one year. Although women have two to three times more hip fractures than men, men with hip fractures die twice as often as women. One study found that six months after a hip fracture, only about 15% of individuals could walk across a room unaided. Many require long-term care. About 20% end up in nursing homes. Quality of life is greatly affected by osteoporosis.
Prevention should begin in childhood and the teenage years with healthy diet and plenty of physical activity to build strong bones. The higher the bone mass density in early adulthood, the greater the chance of avoiding or delaying the effects of osteoporosis.
Individuals need to get the RDA for calcium and vitamin D beginning in childhood and continuing through old age. Exercise at any age is also beneficial in slowing osteoporosis. A BMD test should be done every two years in older individuals. Medicare will usually pay for a BMD test every two years. Signs of osteoporosis should be treated as soon as they appear.
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Tish Davidson, A.M.