Hypertension in Hispanics

A great deal of attention has been paid to the fact that hypertension is more common in African Americans than whites in the United States, the reasons for which have been addressed previously. ¹ Although the facts are not in doubt, there is dispute about the origins of ethnic differences, with some favoring environmental and social factors ¹ and others favoring genetic differences. ² There is a marked inverse gradient of many chronic diseases with socioeconomic status (SES), which has been used to explain the higher prevalence and higher mortality rates of common conditions such as hypertension, heart disease, stroke, and cancer in African Americans than in whites.

The fastest‐growing segment of the US population is persons of Hispanic or Latino descent. This group is overtaking African Americans as the largest US minority group. Between 1980 and 1990 the US Hispanic population increased by 39%, while the overall US population increased by only 7%. ³ Many are recent immigrants who tend to be of relatively low SES. If psychosocial factors are so important in determining the SES gradient of disease it might therefore be expected that Hispanics would also have higher mortality rates than whites. Surprisingly, this does not appear to be the case. According to the National Center for Health Statistics, ⁴ the age‐adjusted death rates for heart disease are 121.9 per 100,000 for whites, 183.3 per 100,000 for African Americans, and 84.2 per 100,000 for Hispanics. For stroke the corresponding figures are 23.3, 41.4, and 19.0, and for cancer 121.0, 161.2, and 76.1. Thus, for all these conditions the rates appear to be lower, not higher, for Hispanics. Relationships between chronic disease, ethnicity, and SES undoubtedly have complex explanations, so findings that seem to go against this gradient are of particular interest to help reveal which factors are relevant. First, we must define who makes up an ethnic group, and in the case of Hispanics this is far from easy.

WHO ARE HISPANICS?

There are two major subgroups of Hispanics in the United States: those from Mexico and Latin America who reside predominantly in states such as Texas and California, and those of Caribbean origin, who reside mostly in the northeastern United States and Florida. Whether they have more or less hypertension than other ethnic groups is an interesting question, and one for which there are surprisingly few data. This is an additionally complex issue because lumping persons together as an ethnic group simply on the basis of common language results in the inclusion of people with very different cultures and ancestries. A white Cuban exile living in Miami, for instance, May have very little in common with someone from the Dominican Republic living in Manhattan or a Mexican immigrant living in San Antonio, TX, but technically all could be called Hispanic.

Most studies have used the National Institutes of Health definitions of race and ethnicity, ⁵ which involve asking subjects two questions: first, “Are you of Hispanic/Spanish origin? (answer yes or no)” and second, “Which of the following best describes your race? (white, black or African American, Eskimo or Aleutian [Alaskan native], Asian or Pacific Islander, or other [specify]).” The San Antonio Heart Study took into consideration respondents' surnames and birthplace as well as their self‐identified ethnicity. ⁶ Reliance on self‐definition has been attacked on the grounds that it is a very crude categorization, but no one has suggested a better method. In the United States the principal ethnic split has been between African American and white, but due to intermarriage this distinction is not always clear. Where do we draw the line? One technique used in the past was to measure skin color, done by using numbered, colored tiles called Van Luschan tiles. These were matched to the skin color on the inner arm of a subject who was classified as dark‐skinned or black if he or she scored between 23 and 30. ⁷ While this approach May have had some objectivity, not much else can be said in its defense. The self‐report method has been rejected by the leaders of the Human Genome Project, who are supporting the use of race‐specific markers such as microsatellite markers, which will require genotyping before population stratification can take place. ⁸ It remains to be seen whether this process will shed much light on ethnic differences in chronic disease.

HYPERTENSION STUDIES IN MEXICAN AMERICANS

The literature on hypertension in Hispanics is both sparse and confusing. The gold standard for defining the prevalence of hypertension in different groups of the US population is the National Health and Nutrition Examination Survey (NHANES). Four surveys have been conducted that included blood pressure measurement. Race/ethnicity was self‐defined by necessity and classified into four groups: non‐Hispanic whites, non‐Hispanic African Americans, Mexican Americans, and other groups. White and African‐American Hispanics who are not Mexican American are put into the last category. To obtain more reliable figures for differences between groups, each survey oversampled African Americans and Mexican Americans. The latest results, published in 2003, ⁵ were based on a survey conducted in 1999 and 2000, and the results were compared with two earlier surveys (1988–1991 and 1991–1994). There were parallel ethnic differences in all three surveys, with non‐Hispanic African Americans having the highest prevalence of hypertension (33.5% in 1999–2000) and Mexican Americans the lowest (20.7%); whites were in the middle (28.9%). The lower rates in Mexican Americans cannot be attributed to better awareness or treatment of hypertension because both measures were lower in this group than in either of the other two groups: in 1999–2000 the percentages of persons with hypertension who were receiving treatment were 60% for African Americans, 63% for whites, and only 40% for Mexican Americans.

One of the few studies to systematically examine the prevalence of hypertension and related diseases in Hispanics, is the San Antonio Heart Study, which compared Mexican Americans with whites. ⁶ Mexican Americans were more obese than the whites and had a dramatically higher prevalence of type 2 diabetes. ⁶ , ⁹ Despite this, the prevalence of hypertension was slightly lower in Mexican Americans, particularly after adjusting for obesity. The issue of culture and ethnicity has been further explored by comparing the data from the San Antonio Heart Study with two other epidemiologic studies that obtained comparable population‐based data. ¹⁰ One was the Mexico City Diabetes Study, and the other was the Spanish Insulin Resistance Study, which was conducted in seven small towns in Spain. In the San Antonio study, the prevalence of hypertension was similar in both whites and Mexican Americans (16% and 19%, respectively), which was the same as Mexicans in Mexico City (19%), but much lower than the Spaniards, where it was 34.5%. Socioeconomic status did not account for these differences—10% of the Mexicans had high school diplomas, whereas 95% of the whites in San Antonio did. When the known factors that might have contributed to these differences were included in a logistic regression analysis (age, gender, education, obesity, alcohol intake), significantly more hypertension was still observed in the Spaniards (odds ratio [OR], 1.53) relative to the San Antonio whites, and significantly less in the Mexicans in Mexico City (OR, 0.67). The prevalence was slightly, but not quite significantly, less in Mexican Americans (OR, 0.86). While it is difficult to explain these differences, the results are at least consistent with the idea that there could be genetic factors that contribute to the lower blood pressure in Mexicans, but they do not support the idea that being labeled Hispanic is in any way related to blood pressure. Whether or not Mexican Americans have less hypertension than whites, there seems to be little doubt that they have less than African Americans. A cohort of more than 200,000 African Americans and Mexican Americans in Los Angeles ¹¹ reported hypertension in 57.5% of the former and 35.8% in the latter; cardiovascular death rates were more than twice as high in African Americans as in the Hispanics.

Some early studies have suggested that, despite higher rates of obesity and diabetes in Mexican Americans, they have a lower all‐cause and cardiovascular mortality than whites, ¹² , ¹³ leading to what has been called the Hispanic paradox. However, the most recent analysis from the San Antonio Heart Study found just the opposite, namely that mortality from cardiovascular disease is about 60% higher in Mexican Americans than whites. ¹³ This is the largest prospective study of Hispanics, so its findings command respect. The authors attribute the contrary findings of the earlier studies to underreporting of deaths in the Mexican Americans.

HYPERTENSION STUDIES IN CARIBBEAN HISPANICS

There is little published information about the prevalence of hypertension and cardiovascular disease in Caribbean Hispanics. One study that has begun to look at the issue is the Northern Manhattan Stroke Study (NOMASS), ³ a case‐control study of patients admitted to area hospitals with a diagnosis of stroke and controls identified by random‐digit dialing from the community, which includes a high proportion of Caribbean Hispanics. In the control group, both hypertension and diabetes were more common in African Americans and Hispanics than in whites: for hypertension the rates were 62%, 58%, and 43%, respectively. An interesting survey was conducted in Cuba, ¹⁴ where everyone can claim to be Hispanic but where there is also a mix of people of European origin (white) and African origin. Subjects classified themselves as blanco(white), mulatto, or negro, the latter two being classified as black. The prevalence of hypertension was only minimally higher in the blacks (46%) than in the whites (43%), which the authors attributed to the fact that socioeconomic differences between blacks and whites are much smaller in Cuba than in the United States. The ethnic difference was also small in comparison with the situation reported in Puerto Rico, where statistical adjustment for social class narrowed the gap between blacks and whites. ¹⁵

ETHNICITY AND 24‐HOUR BLOOD PRESSURE

One feature that relates to ethnicity is the diurnal rhythm of blood pressure. Numerous studies have shown that African Americans are more likely than whites to show a nondipping pattern of blood pressure, which in some, but not all studies, has been related to increased target organ damage. ¹⁶ , ¹⁷ , ¹⁸ , ¹⁹ Only one study has addressed this issue in Hispanics ¹⁹ and found that Hispanic men, but not women, were more likely to be nondippers than whites. However, these were Mexican Americans (the study was conducted in Houston, TX), and no studies to date have reported what happens in Caribbean Hispanics.

THE ROLE OF GENETIC FACTORS

The contribution of genetic factors to ethnic differences in blood pressure remains highly controversial. Although there are many diseases that can be attributed to a single gene mutation (such as glucocorticoid remediable aldosteronism) and that May show genuine ethnic differences (Tay Sachs disease in Ashkenazi Jews is a classic example), it has been argued by Cooper ⁴ and others that racial differences in the prevalence of common complex diseases such as hypertension do not have a primary genetic origin. The discovery of the human genome a few years ago was a major scientific breakthrough, but it led to an unwarranted enthusiasm as to how much of human disease is programmed in our genes. In the case of hypertension, there are huge differences in its prevalence among ethnic or cultural groups, as shown in a recent study where hypertension was more than 50% more common in many West European countries than in the United States or Canada, despite a presumably common gene pool, ²⁰ so it would be surprising if any differences between Hispanics and other ethnic groups in the United States have their basis in genetic factors. Studies of ethnic differences May, however, provide more information about the roles of social and cultural factors on blood pressure.