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Epidemiology
Epidemiology of Osteopenia and Osteoporosis
Osteoporosis has a major public health impact worldwide. In the United States, more than 28 million people are affected. The major clinical consequence of osteoporosis is a greatly increased risk of fracture. Osteoporosis predisposes the population to 1.5 million fractures yearly (including 700,000 vertebral fractures; 250,000 hip fractures; and 250,000 wrist fractures [Riggs and Melton, 1995]), costing more than $13 billion [Ray et al., 1997]. The World Health Organization (WHO) has defined low bone mass and osteoporosis (click here for definition).
A predicted global increase in the elderly population will result in a substantial increase in the prevalence of osteoporosis and subsequent increased risk of fracture. Life expectancies will increase, and it is anticipated that there will be a 4-fold increase in the global fracture rate over the next 50 years [Riggs and Melton, 1995]. The prevalence of osteoporosis has been reported in various ways, by various organizations, including the World Health Organization (WHO), the National Center for Health Statistics, and the National Osteoporosis Foundation.
When evaluating data on prevalence estimates, it should be determined whether the definitions refer to low bone mass, osteopenia, or osteoporosis. Additionally, low bone mass is sometimes used as a general term to refer to all states of bone mass less than the young adult mean (i.e., both osteopenia and osteoporosis). Thus, careful attention should be paid to the definition that is used in studies about these various groups of patients.
National Center for Health Statistics
The National Center for Health Statistics at the Centers for Disease Control and Prevention conducted the third National Health and Nutrition Examination Survey (NHANES III) [Looker et al., 1998,1997,1995].
The purpose of NHANES III was to assess the health and nutritional status of Americans. Data on a random sample of the population were collected through household interviews and standardized physical examinations conducted in specially equipped mobile examination centers. Information on many diseases and risk factors was collected, providing a reference population and prevalence estimates of various public health problems, including osteoporosis.
NHANES III was a 6-year study (1988-1994) divided into two phases: Phase 1 (1988-1991) and Phase 2 (1991-1994). Bone mineral measurements were performed on 14,646 men and women ages 20 and older in the full survey over the 6-year period. The population of men and women was categorized into three ethnic groups: nonhispanic white (NHW), nonhispanic black (NHB), and Mexican American (MA). Estimates of the number of older men and women (ages 50 and older) in the United States with low bone density at the hip (osteopenia and osteoporosis) were made using dual energy X-ray absorptiometry (DXA) measurements gathered in both Phases 1 and 2 of NHANES III.
BMD measurements were obtained at four regions of the hip (see following figure). The mean young normal reference for BMD at the four hip sites was determined by a random sample of NHW men (n=382) and women (n=409), ages 20-29. Four estimates of the prevalence of osteopenia and osteoporosis of men and women were determined by using the normative BMD reference data for each hip region (femoral neck, trochanter, and intertrochanter) and for the total hip.
Four Regions of the Hip
Click on image for larger version.
The following four sections depict some data from NHANES III.
NHANES III Phase 1: Prevalence estimates of osteopenia and osteoporosis for women
NHANES III Phases 1 and 2: Prevalence estimates of osteopenia and osteoporosis for men and women
National Osteoporosis Foundation
Using data from Phase 1 of NHANES III, the National Osteoporosis Foundation (NOF) estimated that about 8 million women and 2 million men have osteoporosis. Moreover, nearly 16 million women and 3 million men have osteopenia and are at increased risk for developing osteoporosis and osteoporotic fracture. Using data from Phases 1 and 2 of NHANES III, the NOF published in the Physician’s Guide to Prevention and Treatment of Osteoporosis that 13-18% (4-6 million) of postmenopausal American women have osteoporosis and an additional 37-50% (13-17 million) of women have low bone density at the hip. Another analysis of NHANES III Phase 1 data, using a different cutoff for the definition of osteoporosis, provided estimates of the number of women ages 50 and older with osteoporosis (BMD more than 2 SD below the young adult mean). Using this cutoff, 14 million women in the United States have osteoporosis and an additional 12 million have low bone mass.
Prevalence data from a different study that used a random sample of women from Rochester, Minnesota [Melton et al., 1992], agreed with the estimates of the prevalence of osteoporosis from NHANES III. Using bone mineral values less than or equal to 2 SD below the mean of young normal women as the criterion for osteopenia, less than 5% (1 of 20) of Caucasian women ages 30-39 are estimated to have low bone mass at any one of the following three sites: hip, spine, or forearm. The prevalence rises to 45.2% in Caucasian women ages 50 or older. In 1992, when these estimates were performed, about 14 million Caucasian women in the United States were believed to have low bone mass.
National Osteoporosis Risk Assessment Program
The National Osteoporosis Risk Assessment (NORA) Program, a national health initiative funded by Merck & Co., Inc. [Siris et al., 1998], enrolled up to 204,000 women nationwide into a comprehensive osteoporosis education and risk assessment program. This initiative created a longitudinal, observational database of postmenopausal women without prior diagnosis of low bone mass, available for continued study by the medical community. Data on the women that was collected at the onset of the program allowed determination of the incidence of osteopenia, osteoporosis, and fractures and provided information on risk factors. In this longitudinal study, repeated observations of these women over time will provide additional information regarding issues such as the natural history of the disease, patient outcomes (e.g., fractures, hospitalizations), treatment choices and effects, cost of the disease, and patient compliance with medication.
Click on the links below for further details on the NORA program.
NORA Objectives
NORA Study Method
NORA BMD Results
Epidemiology of Osteoporotic Fractures
The epidemiology of fractures has been studied in many countries, thus providing basic information for etiologic investigation as well as strategies for preventing and controlling osteoporosis. To obtain data, hospital admissions for fracture have been surveyed in many regions of the world. The numbers of age-related fractures have been calculated from the excess rate compared to the young, healthy community. However, not all fractures are osteoporotic fractures, so the magnitude of the problem is difficult to assess accurately.
International Clinical Data
The association of osteoporotic fractures with advancing age and postmenopausal status is well established. In the United Kingdom, for example, a survey of the Trent Region has shown that the incidence of fractures in men increases from age 65 onward; in women, from age 45 onward [Donaldson et al., 1985]. Thus, the majority of fractures associated with aging occur in postmenopausal women.
Epidemiologic data from various nations show that racial differences in fracture incidence exist. The highest incidence of hip fracture has been found in Scandinavian women older than age 50.
By age 70, more than 25% of European women have sustained at least one osteoporotic fracture. Another part of this investigation, known as the Mediterranean Osteoporosis Study (MEDOS), has collected data from six countries in southern Europe: Portugal, Spain, France, Italy, Greece, and Turkey [Elffors et al., 1994]. The lowest rates of hip fracture were observed in Turkey and the highest in France and Italy. According to the data, the risk of hip fracture is greatest in northern Europe, lower in central Europe, and lowest in southern Europe.
As the size of the elderly population increases, more patients are at risk for fractures. However, the MEDOS Study concludes that the high incidence of osteoporotic fractures is not only related to age but also to factors surrounding the changes in living standards and associated reductions in physical activity observed in the populations of developed countries. Data have demonstrated a higher incidence of fractures in more industrialized areas. The progressive increase in osteoporosis in Western nations is known as the "secular trend."
The incidence of hip fractures was studied in Japan, where it was found to be comparable with other Asian countries, but lower than the incidence in the United States and Europe, despite the lower bone mass in Asians.
Although the incidence of hip fractures in Japan is lower than in the West, the recent trend is toward increasing incidence; however, the aging population is not the only reason for this increase. Other data have shown significant differences in fracture incidence between rural and urban areas of Japan. Higher fracture incidence in urban areas may reflect changes in lifestyle.
Further support for the secular trend comes from a study on the Hong Kong Chinese [Lau et al., 1990]. Incidence of hip fractures in Hong Kong has increased in the last 20 years and is attributed to urbanization and reduced physical activity.
U.S. Clinical Data
A higher incidence of vertebral, hip, and Colles’ fractures has been noted in women older than age 45, in the following graphs.
Incidence Rates for Osteoporotic Fractures in Men and Women
(Rochester, Minnesota)
From Cooper and Melton [1992]; with permission.
Click on image for larger version.
A sharp increase in the fracture rate occurs following menopause. The incidence of Colles’ fractures tends to stabilize, whereas hip fractures increase exponentially in both sexes. The most extensive epidemiologic information comes from a survey of hip fractures over a 55-year period in Rochester, Minnesota [Cooper et al., 1992]. Age-adjusted hip fracture rates in men have increased in North America at the same rate seen elsewhere in the world. Among women, hip fracture rates increased rapidly in Rochester in the years 1930-1955.
This type of rapid increase has also been observed in Scandinavia since 1965. The rate of this rise may be slowing in Europe, as it has in Rochester, although the reason for the leveling effect is unknown.
Incidence of hip fracture
Hip fractures are responsible for the most serious sequelae of osteoporosis, such as long-term care and immobility. In the United States, osteoporosis causes a predisposition to more than 250,000 hip fractures yearly [Ray et al., 1997]. It is estimated that a 50-year-old white woman has a 17.5% lifetime risk of fracture of the proximal femur [Melton et al., 1992]. The incidence of hip fractures increases each decade from the sixth through the ninth for both women and men for all populations. The highest incidence is found among those men and women ages 80 or older [Melton et al., 1992].
National and regional surveys demonstrate dramatic gender and ethnic differences in hip fracture incidence. In the United States population older than age 50, the likelihood of hip fracture is substantially greater for women than for men on an age-adjusted basis. In fact, about 80% of all hip fractures occur in women. The incidence of hip fracture is about 2.4 times greater in Caucasian women than African Americans. Asian Americans have a higher incidence than African Americans, and Mexican Americans have a rate similar to that of African Americans.
Incidence of vertebral fracture
An estimated 700,000 women have a first vertebral fracture each year [Melton et al., 1992]. The lifetime risk of a clinically detected symptomatic vertebral fracture is about 15% in a 50-year-old white woman [Melton et al., 1992]. Many vertebral fractures are asymptomatic and go undetected; thus, the lifetime risk of all vertebral fractures is expected to be much higher.
The prevalence estimated from surveys of X-rays suggests that vertebral fractures affect a high proportion of the elderly. Prevalence has been estimated to vary from 15-75% for individuals ages 70 or older. This variability may be due to the lack of a uniform definition of a vertebral fracture. For example, complete vertebral collapse (i.e., crush fracture) is easily diagnosed, but minor anterior wedging may or may not be classified as an osteoporotic fracture. On average, a 90-year-old woman has a 15-30-fold higher risk of vertebral fracture than a 50-year-old woman.
Incidence of wrist fracture
Distal radius fractures, usually of the Colles' type, are the third most common type of osteoporotic fractures. In the United States, the total annual number of Colles' fractures is about 250,000 [Ray et al., 1997]. The lifetime risk of sustaining a Colles' fracture is about 16% for white women [Melton et al., 1992]. By the time women reach age 70, about 20% have had at least one wrist fracture.
Epidemiologic Studies of Osteoporotic Fractures
NORA Program
NORA, a national health initiative funded by Merck & Co., Inc. [Siris et al., 1998], enrolled up to 204,000 women nationwide into a comprehensive osteoporosis education and risk assessment program. This initiative created a longitudinal, observational database of postmenopausal women without prior diagnosis of low bone mass, available for continued study by the medical community. Data on the women that was collected at the onset of the program allowed determination of the incidence of osteopenia, osteoporosis, and fractures and provided information on risk factors. In this longitudinal study, repeated observations of these women over time will provide additional information regarding issues such as the natural history of the disease, patient outcomes (e.g., fractures, hospitalizations), treatment choices and effects, cost of the disease, and patient compliance with medication.
Click on the links below for further details on the NORA program
NORA Objectives
NORA Study Method
NORA BMD Results
NORA Fracture Incidence ResultsThe NORA program has provided preliminary results on fracture incidence based on 8 months of follow-up of 20,229 women [Miller et al., 1999]. These women had not been diagnosed with osteoporosis before enrollment. The study was conducted through physician offices using peripheral BMD (heel or forearm) measurements. During follow-up, 403 women (2%) sustained 428 new fractures for a rate of 3.06 women with fractures per 100 patient-years.
An analysis of the rate of fracture based on peripheral BMD T-scores showed that the rate of fracture was greatest in the group with the lowest BMD and that the rate decreased with increasing BMD (see table below).
Incidence of Fractures per 100 Patient-Years by T-score and Age in NORA after 8 Months of Follow-Up
T-score </=-2.5 SD* -2.49 <T-score <-1.0† -1.0 < T-score** All women 6.58 3.65 2.12 Ages 50-59 – 3.61 2.12 Ages 60-69 5.87 3.22 2.09 Ages 70-79 5.43 3.37 2.24 Ages 80+ 9.85 7.27 2.96
Additionally, the incidence of fractures appears independent of age among women younger than age 80, whereas incidence increases dramatically among women older than age 80 with low BMD.
Study of Osteoporotic Fractures (SOF)
SOF Objective
SOF Study Method
SOF Fracture Incidence Results
The risk factors that were found to be associated with hip fractures [Cummings et al., 1995] include:
- A maternal history of hip fracture doubled the risk of hip fracture [relative risk=2.0, 95% confidence interval (CI), 1.4-2.9].
- A decrease in weight since age 25 doubled the risk of hip fracture [relative risk=2.2, 95% CI, 1.6-3.0].
- The more weight a woman gained since age 25, the lower her risk of hip fracture. Overall, an increase in weight since age 25 decreased the risk of hip fracture by 40% [relative risk=0.6, 95% CI, 0.5-0.7].
Additional risk factors for hip fracture include:
- Previous fracture of any type after age 50
- Decrease in height since age 25
- Self-rating of health as fair or poor
- Previous hyperthyroidism
- Medications (benzodiazepines or anticonvulsants)
- Greater amount of caffeine intake
- Spending less than or equal to 4 hours per day on feet.
The incidence of hip fracture was 1.1 [95% CI, 0.5-1.6] per 1000 women-years among women with no more than two risk factors and normal BMD of the heel for their age. The incidence of hip fracture increased to 27 (95% CI, 20-34) per 1000 women-years among women with five or more risk factors and low BMD of the heel (lowest third for their age).
Conclusion
Even if age-adjusted rates of fractures remain stable, the aging population will produce an enormous annual increase in the number of hip fractures. On the basis of age alone, it is estimated that the number of hip fractures in Americans older than age 50 may increase from 238,000 in 1986 to 347,000 in 2020. On a worldwide basis, it is estimated that the number of hip fractures could rise to 6.25 million by 2050. Factoring in rising health-care costs, this increase prompts tremendous urgency in finding a cost-effective approach to the prevention of osteoporotic fractures.
References
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