Osteoporosis is a skeletal disorder characterized by compromised bone strength, which predisposes affected individuals to increased risk of fracture. The National Osteoporosis Foundation (NOF; http://www.nof.org/) defines osteoporosis as about 25% bone loss compared with a healthy young adult, or on a bone density test, 2.5 standard deviations below normal. Although some bone loss occurs naturally with advancing age, the stooped posture (kyphosis) and loss of height (greater than one to two inches) experienced by many older adults result from vertebral fractures caused by osteoporosis.
Bone density builds during childhood growth and reaches its peak in early adulthood. From then on, bone loss gradually increases, outpacing the body's natural ability to replace bone. The denser bones are during the growth years, the less likely they will be to develop osteoporosis. Proper diet, especially eating foods rich in calcium and vitamin D long before the visible symptoms of osteoporosis appear, is vitally important.
Osteoporosis worsens with age, leaving its sufferers at risk of broken hips or other bones, curvature of the spine, and other disabilities. An estimated eight million women (non-Hispanic white women are disproportionately affected) have a severe form of the disease, which causes many of them to experience spontaneous (without external causes) fractures, generally in the vertebrae of the spine.
The NOF reports that in 2005 about ten million Americans over age fifty had been diagnosed with osteoporosis, and another thirty-four million were considered at risk of developing the condition (http://www.nof.org/osteoporosis/diseasefacts.htm). Like other chronic conditions that disproportionately affect older adults, the prevalence of bone disease and fractures is projected to increase markedly as the population ages. According to a report issued by the U.S. Surgeon General, each year about 1.5 million people suffer an osteoporotic-related fracture, which often leads to a downward spiral in physical and mental health—about 20% of older adults who suffer hip fractures die within one year (Bone Health and Osteoporosis: A Report of the Surgeon General, Rockville, MD: U.S. Department of Health and Human Services, Public Health Service, Office of the Surgeon General, October 14, 2004, http://www.surgeongeneral.gov/library/bonehealth/content.html).
One out of every two women over age fifty will have an osteoporosis-related fracture in her lifetime, with the risk of fracture increasing with age. The aging of the population combined with the historic lack of focus on bone health may together cause the number of hip fractures in the United States to double or even triple by the year 2020.
About one-third of a person's risk of developing osteoporosis is hereditary. In 1994 an Australian research team identified a gene linked to bone density. Two forms of the gene, B and b, exist. People with two b genes, one from each parent, have the highest bone density and are least likely to develop osteoporosis, whereas those with one of each, the Bb genotype, have intermediate bone density. People with two B genes have the lowest bone density and the highest risk of osteoporosis. Women with the BB genotype may be four times as likely to experience hip fractures as those with the bb genotype (Jane E. Brody, "New Study Links Gene to Risk of Bone Disease," New York Times, January 20, 1994, http://query.nytimes.com/gst/fullpage.html?res=9C0DE6DB1430F933A15752C0A962958260&sec=health&pagewanted=print).
The gene discovery was hailed as the most important finding in the osteoporosis field in a decade. Although much research remains to be done, investigators hope the identification of the gene eventually will lead to a simple test to identify children at risk for osteoporosis in later life. The test would allow doctors to prescribe an
increased intake of calcium and protein during the growth years for these children, thus preventing or delaying the onset of osteoporosis.
Table 6.1 summarizes the factors that predispose a person to osteoporosis and fractures. Apart from genetics, the risk factors—nutrition, physical activity (especially weight-bearing exercise), and choosing not to smoke—are all modifiable. Because the prevalence of osteoporosis and fractures can be reduced via lifestyle
Causes of bone loss and fractures in osteoporosis
Failure to develop a strong skeleton
Genetics—limited growth or abnormal bone composition
Nutrition—calcium, phosphorous and vitamin D deficiency, poor general nutrition
Lifestyle—lack of weight-bearing exercise, smoking
Loss of bone due to excessive breakdown (resorption)
Decreased sex hormone production
Calcium and vitamin D deficiency, increased parathyroid hormone
Excess production of local resorbing factors
Failure to replace lost bone due to impaired formation
Loss of ability to replenish bone cells with age
Decreased production of systemic growth factors
Loss of local growth factors
Increased tendency to fall
Loss of muscle strength
Slow reflexes and poor vision
Drugs that impair balance
SOURCE: "Table 2-2. Causes of Bone Loss and Fractures in Osteoporosis," in "Chapter 2: The Basics of Bone in Health and Disease," Bone Health and Osteoporosis: A Report of the Surgeon General 2004, U.S. Department of Health and Human Services, Public Health Service, Office of the Surgeon General, 2004, http://www.surgeongeneral.gov/library/bonehealth/chapter_2.html (accessed January 16, 2006) TABLE 6.2 Healthy People 2010 osteoporosis and bone health objectives "Table 1-1. Healthy People 2010 Osteoporosis and Bone Health Objectives," in "Chapter 1: A Public Health Approach to Promote Bone Health," Bone Health and Osteoporosis: A Report of the Surgeon General 2004, U.S. Department of Health and Human Services, Public Health Service, Office of the Surgeon General, 2004, http://www.surgeongeneral.gov/library/bonehealth/chapter_1.html (accessed January 16, 2006)
|Healthy People 2010 osteoporosis and bone health objectives
|Healthy People 2010 objective number
||Healthy people 2010 objective
SOURCE: "Table 1-1. Healthy People 2010 Osteoporosis and Bone Health Objectives," in "Chapter 1: A Public Health Approach to Promote Bone Health," Bone Health and Osteoporosis: A Report of the Surgeon General 2004, U.S. Department of Health and Human Services, Public Health Service, Office of the Surgeon General, 2004, http://www.surgeongeneral.gov/library/bonehealth/chapter_1.html (accessed January 16, 2006)
||Reduce cases of osteoporosis
||10 percent of adults aged 50 years and older had osteoporosis as measured by low total femur bone mineral density (BMD) in 1988–94 (age adjusted to the year 2000 standard population).
||Reduce hospitalizations for vertebral fracture
||17.5 hospitalizations per 10,000 adults aged 65 years and older were for vertebral fractures associated with osteoporosis in 1998 (age adjusted to the year 2000 standard population).
||14.0 hospitalizations per 10,000 adults aged 65 years and older
||Reduce hip fractures
||Females aged 65 years and older
||1,055.8 per 100,000
||416 per 100,000
||Males aged 65 years and older
||592.7 per 100,000
||474 per 100,000
||Increase calcium intake
||46 percent of persons aged 2 years and older were at or above approximated mean calcium requirements (based on consideration of calcium from foods, dietary supplements, and antacids) in 1988–94 (age adjusted to the year 2000 standard population).
||Increase physical activity (there are 15 objectives for increasing physical activity)
modification, Healthy People 2010, the nation's plan for improving the health of Americans, aims to reduce the number of cases of osteoporosis and hospitalizations for fractures, as well as increase calcium intake by Americans. (See Table 6.2.)
Treatment of Osteoporosis
The primary goal of therapy is to prevent fractures. Nonpharmacologic (without medicine) preventive measures to help prevent osteoporosis include diet modification (an increase in the intake of calcium and vitamin D), exercise programs, and fall-prevention strategies. Current pharmacologic (medication) therapies improve bone mass and reduce fracture risk.
At the end of the twentieth century, the traditional treatment for postmenopausal women with osteoporosis, or those at risk for the disease, was hormone replacement therapy (HRT), often combined with daily doses of calcium and regular weight-bearing exercise, such as walking and exercising with weights. This treatment slows the advance of the disease and helps to prevent fractures and disability. Because serious side effects of HRT were publicized in July 2002—including documented increased risks of cardiovascular disease and certain types of cancer—many women discontinued HRT treatment. For some women at heightened risk for osteoporosis who also have fewer risk factors for cardiovascular disease, HRT remains a treatment option.
One of the goals of the treatment of osteoporosis is to maintain bone health by preventing bone loss and by building new bone. Another is to minimize the risk and
FIGURE 6.3 The osteoporosis pyramid for prevention and treatment "Figure 9-1. The Osteoporosis Pyramid for Prevention and Treatment," in "Chapter 9: Prevention and Treatment for Those Who Have Bone Diseases," Bone Health and Osteoporosis: A Report of the Surgeon General 2004, U.S. Department of Health and Human Services, Public Health Service, Office of the Surgeon General, 2004, http://www.surgeongeneral.gov/library/bonehealth/chapter_9.html (accessed January 16, 2006)impact of falls, because they can cause fractures. Figure 6.3 shows the pyramid of prevention and treatment of osteoporosis. At its base is nutrition, with adequate intake of calcium, vitamin D, and other minerals; physical exercise; and preventive measures to reduce the risk of falls. The second layer of the pyramid involves identifying and treating diseases that can cause osteoporosis, such as thyroid disease. The peak of the pyramid involves drug therapy for osteoporosis.
There are two primary types of drugs used to treat osteoporosis. Antiresorptive agents act to reduce bone loss, and anabolic agents are drugs that build bone. Antiresorptive therapies include use of bisphosphonates, estrogen, selective estrogen receptor modulators (SERMs), and calcitonin. Antiresorptive therapies reduce bone loss, stabilize the architecture of the bone, and decrease bone turnover. In 2005 the FDA approved two bisphosphonates—alendronate and risedronate—for prevention or treatment of osteoporosis and one anabolic agent—a synthetic form of parathyroid hormone known as teriparatide that is administered by injection.
EXERCISE IMPROVES BONE HEALTH IN OLDER ADULTS
The first study to examine the impact of exercise independent of other factors, primarily diet, on bone mineral density and the risk of osteoporosis and fractures confirmed that exercise helps to maintain and, in some cases, improve bone mass in persons ages fifty-five to seventy-five. Researchers at Johns Hopkins University School of Medicine in Baltimore, Maryland, followed 104 older men and women and found that six months of aerobic exercise using a bicycle, treadmill, or stepper, combined with weightlifting, resulted in improved overall fitness and fat loss without significant change (loss) in bone mineral density. Further, the study participants who exercised the hardest and had the greatest increases in aerobic fitness, muscle strength, and muscle tissue showed bone mass increases of 1% to 2% (Kerry Stewart et al., "Exercise Effects on Bone Mineral Density: Relationships to Change in Fitness and Fatness," American Journal of Preventive Medicine, vol. 28, no. 5, June 2005).