19.1

Introduction

In this chapter, we first address some of the problems inherent in using a racial classification system for describing human variation. We then describe variations in bone and mineral metabolism and fracture risk that have been observed between and within “racial” or ethnic groups. We concentrate on race/ethnic differences in fracture rates within the United States since Chapter 20 , Geographic variability in the incidence of hip and vertebral fractures, reviews worldwide differences in fracture rates. We also concentrate on adults age 50 years or older. For race/ethnic differences in changes in bone strength over the menopausal transition, refer to Chapter 24 , Clinical and epidemiological studies. As race/ethnic differences in risk of osteoporosis should be interpreted with caution, they are all too often treated in an overly simplistic manner. They can be affected by technological differences in measurements, variations in use of reference data, geographic differences, and a myriad of biological and cultural factors.

19.2

Background and definitions

“Ethnicity” and “race” appear interchangeably in many publications. “Race” in the United States reflects the belief that a limited number of genetically characterized human groups exist, exemplified by the list to be used by the 2020 US Census, although individuals will be able to select among 15 subcategories or write them in. The main categories are White, Black or African-American, American-Indian or Alaska Native, Asian/Pacific Islander (with a number of choices), and “some other race.” Hispanic, Latino, or Spanish origin is asked separately. Most investigators recognize, however, that distinct racial lines may not be drawn due to significant genetic admixture and other evolutionary forces that have occurred over time. Also, because environments change, and because populations move and interbreed, it is difficult if not impossible to identify discrete, biologically meaningful subgroups of humans.

A factor that reflects cultural, religious, dietary, geographic, and other differences between groups, known as ethnicity, then becomes important . Lack of ethnic definition of study groups affects the general applicability of data. A study reporting hip fracture rates of “Asians” may apply only to a specific Asian group, such as Japanese, but not to Koreans or another Asian group. For example, in a study comparing the mean bone mineral density (BMD) of Japanese, Korean, and Taiwanese women, the Taiwanese had consistently greater BMD at the lumbar spine at almost every age .

Assessment of ethnic and geographic variations helps describe disease occurrence among human groups, such as the description of factors that may affect observed differences in fracture rates. For this reason, as well as the pitfalls associated with “race” described earlier, we attempt to use “ethnic” with “race” in most of the contexts that follow. Data are frequently reported using “racial” categorizations without indication of ethnic grouping. We present those data as reported. Finally, race plays a role in the knowledge, attitudes, and beliefs of women with osteoporosis, which will influence racial disparities .

19.3

Ethnoepidemiology of osteoporosis

Great variation in the occurrence of osteoporotic fractures exists worldwide and within and among different racial and ethnic groups (see Chapter 20 : Geographic variability in the incidence of hip and vertebral fractures). Some studies report wide ranges in hip fracture incidence rates within a given racial group, probably due to regional and/or lifestyle factors. In what follows we concentrate on race/ethnic differences in fracture rates within the United States.

19.4

Ethnic differences in US hip fractures

Broad conclusions can be drawn regarding differences in hip fracture rates among US Whites and Blacks with more limited data on Hispanics and Asians. Early studies from a 5% sample of Medicare beneficiaries, including more than 26,000 hip fractures, demonstrated that rates in 1986 increased with age in both men and women, Blacks and Whites. The black/white ratio in rates differed by age in women ranging from 0.42 in women age 65–69 years to 0.73 in women age 95–99 years. The black/white ratio in men ranged from 0.75 in men age 65–69 years to 0.36 in men aged 90–94 years, but there were few hip fractures in men in this oldest age-group .

Karagas et al. compared femoral neck and trochanteric hip fractures in a 5% Medicare sample of US Whites and Blacks (1986–90). Incidence of each type of hip fracture increased with age in both Whites and Blacks, men and women. The age-adjusted incidence of femoral neck hip fractures (per 100,000) was 218, 123, 433, and 191 in white men, black men, white women, and black women, respectively, following the overall pattern of all hip fractures. Rates of trochanteric hip fractures (per 100,000) were 2.8, 124, 423, and 154 in white men, black men, white women, and black women, respectively. Rates of each type of hip fracture were similar within each race and sex group.

Lauderdale et al. used a 1992 sample of Medicare enrollees, including a 50% sample of Hispanics and a 10% sample of Whites, Blacks, and Native Americans . Hispanic ethnicity was assigned by Spanish surnames. To separate the Hispanic population by ancestry, the authors used the 1990 census Public Use Microdata to identify states where the Hispanic elderly population is overwhelming of one ancestry: Texas and Arizona Mexican Americans (MAs) and Florida (Cubans).

Puerto Ricans were identified as those living in Puerto Rico. Hip fractures were identified by ICD code. Traumatic and pathologic fractures were excluded. Age-adjusted rates (per 100,000) were 220, 430, 730, and 1010 for Hispanic men, white men, Hispanic women, and white women, respectively. Overall rates in Hispanics were 0.75 observed in Whites. Within Hispanic subgroups, rates were greatest in MAs, followed by Cubans and Puerto Ricans.

The Hispanic Established Populations for the Epidemiologic Study of the Elderly (H-EPESE), a longitudinal study of a representative sample of 2895 MAs age 65 years and older in the southwestern United States, used a complex acculturation algorithm for MA heritage. The algorithm takes into account father’s Spanish versus non-Spanish surname, mother’s maiden name, both parents’ birthplace, subject’s self-identification, and ethnic background of all four grandparents . Results showed an overall incidence of hip fracture (per 100,000) in Hispanic women of 930 [95% confidence interval (CI)] (890–970) and Hispanic men of 480 (95% CI) (106–860). These rates are even higher than rates reported in US Medicare beneficiaries (1984–87) of 428 and 807 (per 100,000) for white men and white women, respectively. However, as noted earlier, H-EPESE study relied on a complex algorithm for identifying Hispanic heritage, and the population may not be representative. In addition, they relied on self-report of hip fracture and were unable to exclude major trauma.

Silverman and Madison examined hip fracture hospital discharge rates for the state of California in 1983–84. Age-adjusted rates per 100,000 of hip fracture were 140.7, 49.7, 57.3, and 85.4 in White, Hispanic, Black, and Asian women, respectively, and 48.9, 22.2, 38.7, and 26.3 in White, Hispanic, Black, and Asian men, respectively. These hip fracture rates among Hispanics were similar to those from Mexico City, Mexico in women but higher than rates in men living in Mexico .

Hip fracture hospitalization rates for Non-Hispanic Whites (NHW), Blacks, Hispanics, and Asians were estimated for New York City in 1988–2002 . Hip fracture hospitalization rates per 100,000 were in men 220.3, 87.2, 109.4, and 104.0 in Whites, Hispanics, Blacks, and Asians, respectively, and in women 459.0, 143.1, 137.4, and 173.6 in Whites, Hispanics, Blacks, and Asians, respectively. Hispanics in New York are likely of different heritage than Mexican Americans, which may contribute to the observed difference in rates.

There are limited data comparisons within Asian groups. Lauderdale et al. used surnames within the Medicare data (1992) and showed that the age-adjusted hip fracture incidence was lower for all three Asian-American groups than for Whites . For women, standardized fracture ratio relative to Whites was 0.30 for Chinese, 0.73 for Japanese, and 0.53 for Koreans. For men the standardized hip fracture ratio was 0.42 for Chinese, 0.58 for Japanese, and 0.90 for Koreans. The use of surnames to identify ethnicity may be problematic, especially for women.

To address whether or not these differences in hip fracture rates were related to environment or lifestyle, Ross et al. compared hip fracture rates in men and women of Japanese ancestry living in Oahu, Hawaii from 1979 to 1981 to rates for Japanese living in Okinawa, Japan from 1984 to 1985, and rates in Caucasians (Rochester, Minnesota) from 1978 to 1982. Age-specific and cumulative rates of hip fracture among people of Japanese ancestry were approximately half that of Caucasians with little detectable difference in rates between Oahu, Hawaii and Okinawa, Japan. A further study included comparison between Japanese living in Hawaii and Caucasians living in Hawaii and found no difference primarily because rates of hip fracture were low among the Hawaiian-Caucasians .

To our knowledge, there are few data on hip fracture rates in American-Indians. In the Women’s Health Initiative (WHI), during a mean of 7.6 years, 5 of 417 (0.4%) American-Indians experienced a hip fracture . Among First Nations people in Canada, rates of hip fracture were about twofold higher than Caucasians in Canada .

Most of these early papers reported rates of hip fracture by race from 1986 to 1993 . To our knowledge, the most recent data by race ethnicity are from 2000 to 2009 . Wright et al. updated hip fracture rates in the United States using data from a 5% sample of Medicare enrollees . Self-reported race/ethnicity was used based on social security administration records. A total of 821,475 women and 632,162 men were included in the analysis each year. As shown in Table 19.1 , rates were highest in white women followed by Hispanics, Asians, and Blacks. For men, rates were highest in Whites, followed by Hispanics, Blacks, and Asians. Using data from 2008 to 2009, the rate ratio of hip fracture compared to white women was 0.42, 0.51, and 0.71 and compared to white men, 0.67, 0.50, and 0.81 in Blacks, Asians, and Hispanics, respectively. A significant decreasing trend in hip fractures was observed among white men (8% decline) and women (14% decline), similar to a previous report from 1995 to 2005 . However, trends varied by race/ethnicity (see Figs. 19.1 and 19.2 ). Declines were more modest for non-Caucasians overall but separate examination by age revealed significant declines in hip fracture in White (−24.5%), Black (−23.8%), and Asian (−21.6%) women age >75 years. Results were similar in men, although the declines were smaller: Whites (−13.3%), Blacks (−20.7%), Asians (−31.8%), and Hispanics (−5.7%). The declines were statistically significant for white women, black women, and white men age 75 years or older. Unlike a previous report from California , hip fracture rates in Hispanics were not increasing. These decreasing trends may reflect increasing availability and use of osteoporosis therapies, and increasing emphasis on lifestyle (calcium/vitamin D/physical activity). In addition, the epidemic of obesity may also contribute.

Age-standardized hip fracture incidence in women from 2000 to 2009 by race/ethnicity.

Reproduced with permission from Wright NC, Saag KG, Curtis JR, Smith WK, Kilgore ML, Morrisey MA, et al. Recent trends in hip fracture rates by race/ethnicity among older US adults. J Bone Miner Res 2012;27(11):2325–32.

Age-standardized hip fracture incidence in men from 2000 to 2009 by race/ethnicity .

Reproduced with permission from Wright NC, Saag KG, Curtis JR, Smith WK, Kilgore ML, Morrisey MA, et al. Recent trends in hip fracture rates by race/ethnicity among older US adults. J Bone Miner Res 2012;27(11):2325–32.

Updated analysis of US Medicare claims data from 2002 to 2015 found that age-adjusted hip fracture rates declined from 2002 to 2012 but rates for 2013, 2014, and 2015 were higher than projected, resulting in 11,000 more hip fractures . These data suggest that the decline in hip fracture rates has stopped perhaps due to declines in BMD testing and dual-energy X-ray absorptiometry (DXA) availability . These authors did not report whether these patterns differed by race/ethnicity.

19.5

Hip fracture rate by immigration status

Many countries in Europe are experiencing increasing immigration . There is emerging data on fracture rates in immigrants compared to native born in the United Kingdom and Sweden . The UK data included over three million patients, age 30–100 years (50% men) in the derivation cohort, and reported the incidence of hip, distal, radius, vertebra, or proximal humerus fractures from 1993 to 2011. The Swedish data focus only on hip fracture and included men and women, age 50 years or older in Sweden between 1987 and 2001. The results of the two studies are summarized in Table 19.2 .

In the UK data, all immigrants had significantly lower major osteoporotic fractures, 25%–77% lower in comparison to Whites. Patterns were similar in analyses confined to hip fracture only. In the Swedish-born cohort, hip fracture incidence was almost twice that of immigrants. Hip fracture incidence rose slowly with time from immigration but remained significantly lower than that for Swedish-born individuals.

19.6

Ethnic differences in other fractures

Early data from Medicare/Medicaid showed lower distal forearm and proximal humerus fracture in Blacks compared to Whites . More recently, the incidence of nonspine fractures (per 100,000) was 1090, 580, 3170, and 1680 in white men, black men, white women, and black women, respectively, in subjects age 70–79 years . However, the number of fractures was very low in Blacks: 11 fractures in black men and 39 fractures in black women.

Among women enrolled in the WHI, clinical fracture rates per 100,000 were 2000, 900, 1300, 1200, and 2000 in Whites, Blacks, Hispanics, Asians, and American-Indians . In the National Osteoporosis Risk Assessment (NORA) study, individual fracture rates were not provided but the relative hazard ratios (HR) of fracture (95% CI) compared to Whites were Blacks, HR 0.54 (95% CI 0.41–0.72); Native Americans, HR 0.89 (95% CI 0.59–1.30); Hispanics, HR 0.91 (95% CI 0.72–1.15); and Asians, HR 0.41 (05% CI 0.21–1.79) .

Medicare claims data from 2000 to 2005 were used to examine demographic factors associated with incident nonspine, nonhip fractures . ICD-9 coding and procedure coding were used to identify incident hip, spine, distal radius, ulna, humerus, ankle, and tibia/fibula fractures. As shown in Table 19.3 , ratios were lowest for US Blacks for all sites except ankle and tibia/fibula fractures that were lowest among Asian-Americans. A recent report from the Osteoporotic Fractures in Men Study (MrOS) reported no race/ethnicity differences in wrist fracture, but ethnic minorities accounted for only 10% of the cohort and power were low . Radiographic vertebral fractures, the most common osteoporotic fractures show much less variability in women by race/ethnicity and geography ( Fig. 19.3 ). US black women have the lowest prevalence but the prevalence is similar in Japanese, Chinese, and Mexican women. It is important to note that different methodologies and definitions were used to define morphometric fractures across these studies.

Prevalence of morphometric vertebral fracture in women by age, race, or geographic location.

Modified from Cummings SR, Melton LJ. Epidemiology and outcomes of osteoporotic fractures. Lancet 2002;359(9319):1761–7. Cauley JA, Palermo L, Vogt M, Ensrud KE, Ewing S, Hochberg M, et al. Prevalent vertebral fractures in black women and white women. J Bone Miner Res 2008;23(9):1458–67. Clark P, Cons-Molina F, Deleze M, Ragi S, Haddock L, Zanchetta JR, et al. The prevalence of radiographic vertebral fractures in Latin American countries: the Latin American Vertebral Osteoporosis Study (LAVOS). Osteoporos Int 2009;20(2):275–82. Horii C, Asai Y, Iidaka T, Muraki S, Oka H, Tsutsui S, et al. Differences in prevalence and associated factors between mild and severe vertebral fractures in Japanese men and women: the third survey of the ROAD study. J Bone Miner Metab 2019;37(5):844–53.

In summary, many studies of racially diverse populations in the United States have consistently reported higher rates among Whites than among other racial and ethnic groups. Rates among US Hispanics are intermediate between the lower US black rates and the higher white rates . The analysis of Medicare data for individuals age 65 years and older found that age-adjusted hip fracture incidence rates were lower for all Asian groups (Chinese, Japanese, and Korean-Americans) than for Whites .

Of interest are racial and ethnic differences with respect to the magnitude of the female:male ratio of hip fracture incidence rates, which usually exceeds two in NHW populations. Among black Americans, hip fracture is more common among women than men; however, the female:male ratio is usually below 2. In the studies conducted in Hispanic populations, the gender ratio is close to 2 . All studies but two in Asian populations demonstrate a higher incidence of hip fracture in Asian women than men, with two studies reporting female:male ratios that exceed 3.0 . In the 2012 report using Medicare data the female:male ratio in hip fracture was 1.86 for Whites, 1.16 for Blacks, 1.89 for Asians, and 1.62 for Hispanics .

Increasing age is an established risk factor for hip fracture in all racial and ethnic groups. An excellent albeit old review of differences in age-specific incidence rates of hip fracture between racial and ethnic groups is provided by Maggi et al. . Although hip fracture incidence increases with age in all ethnic groups, the increase occurs earlier in NHW populations than in US black, Asian, and Hispanic populations . Studies conducted in NHW populations report higher rates of hip fracture among men than women before 50 years of age, whereas after age 50 years, women have higher rates than men.

Environmental lifestyle factors, such as urbanization, diet, level of physical activity, obesity, frequency of cigarette smoking, alcohol intake, and use of hormonal medications, may explain some of the differences in hip fracture incidence observed between racial and ethnic groups. Factors that may contribute to racial and ethnic differences in skeletal health and risk for hip fracture are discussed in the remainder of this chapter.

19.7

Ethnic patterns in bone strength measures

The term “bone mass” can refer to a variety of measurements, including bone mineral content (BMC; in g), areal BMD (aBMD; in g/cm ² ), and volumetric BMD (vBMD; in g/cm ³ ), although strictly the term should be used only when referring to total BMC. The magnitude of ethnic differences in bone mass reported by various investigators varies with the measurement used as well as other factors. The most important of these is body size (especially body weight), as bone size and therefore bone mass vary directly with body size. Many interethnic and interracial studies in adults do not adjust for differences in body stature, making comparisons difficult.

19.7.3

Trabecular bone score

Trabecular bone score (TBS) was developed as an indirect measure of vertebral bone microarchitecture derived from texture analysis of spine DXA scans and has been shown to predict fracture independent of aBMD . The Fracture Risk Assessment tool, FRAX has also incorporated TBS into its fracture probability algorithm . As it is based on lumbar spine DXA scans, the TBS may be influenced by degenerative changes in the spine and by body composition, thus care must be taken when interpreting TBS measurements.

Notably, there is little and conflicting information on race/ethnic differences in TBS. The best data come from NHANES because it is a large sample and representative of US adults . TBS declined cross-sectionally by age in each race/ethnic group in both men and women. However, there were significant age×sex and sex by race/ethnicity interaction, Table 19.5 .

Table 19.5

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