doi: 10.1161/hy0202.103439
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(Hypertension. 2002;39:203.)
© 2002 American Heart Association, Inc.
Scientific Contributions |
Prevalence of Hypertension in Hispanic and non-Hispanic White Populations
From the Department of Medicine, Division of Clinical Epidemiology, University of Texas Health Science Center at San Antonio (C.L., K.W., M.P.S., H.P.H., S.M.H.); Department of Internal Medicine, Hospital Universitario de San Carlos (M.S-R., M.T.M-L.), Madrid, Spain; Department of Clinical Epidemiology, Hospital de La Princesa (R.G.), Madrid, Spain; and Center of Studies in Diabetes, American British Cowdray Hospital (C.G-V.), Mexico City, Mexico.
Correspondence to Carlos Lorenzo, MD, Department of Medicine, Division of Clinical Epidemiology, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Dr, San Antonio, TX 78284-7873. E-mail lorenzo{at}uthscsa.edu
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Abstract |
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Mexican nationals in Mexico City and Mexican Americans in San Antonio, Tex, have a lower adjusted prevalence of hypertension than San Antonio non-Hispanic whites, especially after adjusting for the greater obesity of San Antonio Mexican Americans. The concomitant examination of a new study from Spain may better explain the association of genetic and environmental factors with hypertension. Three population-based epidemiological studies conducted in Mexico City, Spain, and San Antonio, Tex, were available for comparisons. Hypertension was defined as systolic blood pressure
140 mm Hg, diastolic blood pressure 90 mm Hg, or the use of antihypertensive medications. The prevalence of hypertension was independently associated with age, body mass index, glucose tolerance, and alcohol consumption, with comparable degrees of relationship in all 4 populations. Relative to San Antonio non-Hispanic whites, an excess prevalence of hypertension was observed in Spaniards (odds ratio [OR], 1.53; 95% confidence interval [95% CI], 1.24 to 1.90). A deficit in hypertension prevalence was statistically significant in Mexican nationals (OR, 0.67; 95% CI, 0.53 to 0.85) and close to significance in San Antonio Mexican Americans (OR, 0.86; 95% CI, 0.71 to 1.03). Thus, obesity, educational attainment, type 2 diabetes, glucose tolerance, and marked alcohol consumption (14 drinks/wk) do not fully explain the increased prevalence of hypertension in Spain and the lower prevalence of hypertension in Mexican-origin populations. Although we cannot conclude definitively that these differences are genetically driven, our results suggest no relationship between Spanish genetic admixture and the deficit in hypertension prevalence in Mexican-origin populations.
Key Words: clinical trials • diabetes • obesity • epidemiology
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Introduction |
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In San Antonio, Tex, as in other places of the United States, Mexican Americans (SA-MAs) have a slightly lower prevalence of hypertension than non-Hispanic whites (SA-NHWs). After the adjustment for the greater obesity and lower socioeconomic status, the prevalence of hypertension becomes much lower in SA-MAs than in SA-NHWs.1–4 In comparisons between 2 populations with similar genetic admixture, Mexicans from Mexico City and SA-MAs, low-income participants have a lower prevalence of hypertension in Mexico than in San Antonio.1,5 The assumption that genetic susceptibility is similar in native Mexicans and SA-MAs derives from population estimates of similar genetic admixture in San Antonio and Mexico based on skin color and genetic markers.6,7 The addition of a new epidemiological study from Spain may clarify the role of Mexican genetic admixture on the prevalence of hypertension because of the genetic and cultural contributions of Spain to Hispanic communities in Mexico and the United States.
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Methods |
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The San Antonio Heart Study and the Mexico City Diabetes Study
The San Antonio Heart Study (SAHS) and the Mexico City Diabetes Study (MCDS) are population-based studies on cardiovascular disease that share identical protocols. Survey procedures have been published previously.8–11 In the SAHS, households from low-, middle-, and high-income neighborhoods were randomly sampled. Ethnic classification (Mexican American and non-Hispanic white) was based on a previous published algorithm.8 A total of 5158 men and nonpregnant women, age 25 to 64 years, participated in the SAHS (overall response rate, 65.3%). Of those, 3682 subjects completed a 8-year follow-up visit.9,10 Data from the SAHS follow-up visits were used for comparisons because of the lower differences in the mean age among studies. In the MCDS, households from a low-income area of Mexico City were randomly selected. A total of 2282 men and nonpregnant women, age 35 to 64 years, completed the survey (overall response rate, 65.1%).11 All subjects in both studies gave informed consent.
The Spanish Insulin Resistance Study
Spanish Insulin Resistance Study (SIRS) is a population-based study on cardiovascular risk factors conducted in 7 small and middle-size towns across Spain. From a targeted population of 348 980 inhabitants, age 34 to 69 years,12 a total of 2949 men and nonpregnant women completed the survey (overall response rate, 66.9%). Survey procedures were adapted from the World Health Organization MONICA Project (WHO MONICA) protocol.13 One of the SAHS and MCDS investigators (S.H.) contributed to the design of SIRS, although SIRS medical staff received no cross training. All subjects gave informed consent.
Definition of Variables
Educational attainment was treated as a dichotomous variable (having and not having obtained high school diploma). Waist circumference was measured at the level of the umbilicus. Overall adiposity was assessed by body mass index (BMI); central fat distribution, by waist circumference. Alcohol consumption and current smoking were estimated by interview. Systolic (SBP) and diastolic (DBP) blood pressure (first and fifth Korotkoff sounds, respectively) were measured to the nearest even digit and were reported as the mean of the first and second SBP and DBP readings. Subjects with SBP 140 mm Hg or DBP 90 mm Hg or subjects currently using antihypertensive medications were considered to have hypertension.14 Type 2 diabetes was defined as fasting plasma glucose level 7.0 mmol/L and/or 2-hour glucose 11.1 mmol/L. Diabetic subjects taking oral antidiabetic medications or those taking insulin with a BMI >27 and age at onset >30 years were considered to have type 2 diabetes. In nondiabetic subjects, impaired glucose tolerance (IGT) was defined as 2-hour glucose level between 7.8 mmol/L and 11.1 mmol/L.15
Statistical Methods
Statistical analyses were performed with the SAS statistical software (SAS Institute). Age-adjusted differences in continuous variables between the studied populations were evaluated by 1-way ANCOVA. Population was used as the grouping variable, and the others were covariates. Logistic regression models identified variables independently associated with the prevalence of hypertension. Age, gender, education, obesity, glucose tolerance, alcohol consumption, and smoking interactions with population were also considered. All probability values are 2-sided.
An expanded Methods section can be found in an online data supplement available at http://www.hypertensionaha.org.
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Results |
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In men and women, comparisons among populations were significantly different for mean age, educational attainment, and age-adjusted indices of obesity (Table 1). In men, BMI was especially high in SA-MAs, and waist circumference was high in both San Antonio populations. In women, BMI and waist circumference were higher in Mexican-origin populations than in European-origin populations and in women from Spain than in SA-NHWs.
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Men had higher age-adjusted SBP than women in Mexico (P<0.0001), SA-MAs (P<0.0001), and SA-NHWs (P=0.002) but not in Spain (P=NS). In men, SBP was higher in Spain than in Mexico and in SA-NHWs (P<0.0001 for both comparisons), but SBP was similar in Spanish populations and SA-MAs (P=NS). In women, SBP was higher in Spain than in the other 3 populations (P<0.0001 for all comparisons). Men had higher age-adjusted DBP than women in Mexico (P<0.0001), SA-MAs (P<0.0001), SA-NHWs (P<0.0001), and Spanish populations (P=0.009). In men, DBP was higher in Spain than in Mexico (P=0.006), in SA-MAs (P<0.0001), and in SA-NHWs (P<0.0001). In women, DBP was higher in Spain than in the other 3 populations (P<0.0001 for all comparisons).
In comparisons between men and women, the age-adjusted prevalence of hypertension was not significantly different in any of the populations. Men in Spain had higher hypertension prevalence than those in Mexico (P<0.0001), SA-MAs (P=0.005), SA-NHWs (P<0.0001), and women in Spain more than women in Mexico or San Antonio (P<0.0001 for all 3 comparisons). Type 2 diabetes was more prevalent in both Mexican-origin populations than in those of European ancestry. In comparisons between Spanish subjects and SA-NHWs, differences in the prevalence of type 2 diabetes were near significance in men (9.9% versus 7.0%, P=0.094) and were significant in women (8.4% versus 5.6%, P=0.022). Alcohol consumption was higher in men than in women (P<0.0001 for all comparisons). Men had higher alcohol intake in Spain than in the other 3 populations (P<0.0001 for all comparisons), and women had higher alcohol consumption in SA-NHWs and Spain than in Mexico and SA-MAs (P<0.0001 for all comparisons). Men smoked more than women in all populations (P<0.0001 for all comparisons) but SA-NHWs (P=NS). Men smoked less in San Antonio than in Spain and Mexico (P<0.0001 for all comparisons). Population differences in the prevalence of current smoking were less marked in women.
Because the diagnosis of hypertension has clinical consequences and antihypertensive medications lower blood pressure values, we selected the prevalence of hypertension instead of blood pressure values for subsequent comparisons. Compared with age-matched men, a lower prevalence of hypertension in women age 35 to 44 years was statistically significant in Mexico (P=0.019), SA-NHWs (P=0.025), and Spain (P<0.0001) and was close to significance in SA-MAs (P=0.053) (Figure 1a and 1b). However, older women had similar prevalence in all 4 populations or even higher prevalence in Spanish women age 55 to 64 years (P<0.0001). An association trend between the age- and gender-adjusted prevalence of hypertension and BMI was observed in each population (Cochran-Armitage trend test, P<0.0001 for all comparisons) (Figure 2a). Lower hypertension prevalence in high school graduates was demonstrated in Spain (P<0.0001) and in SA-MAs (P=0.017) (Figure 2b). The prevalence of hypertension was higher in participants with type 2 diabetes and IGT than in those with normal glucose tolerance (Figure 2c) and was also higher in participants with alcohol consumption 14 drinks/wk (Figure 2d).
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Table 2 shows a multiple logistic regression analyses on the prevalence hypertension for each one of the populations. As independent variables, we included age (10-year increments), gender (male versus female), BMI (tertiles), educational attainment (having versus not having obtained high school diploma), glucose tolerance category (type 2 diabetes, IGT, and normal), current smoking (yes versus no), and alcohol consumption (14 versus <14 drinks/wk). Odds ratio (OR) for age ranged between 2.00 and 2.15. This means that the odds of having hypertension doubled for every 10-year increment of age in each population. A higher prevalence of hypertension was observed in participants in the highest and middle categories of BMI, with a comparable degree of association across populations. Hypertension prevalence was associated with IGT as much as with type 2 diabetes in all 4 populations, and so was it with alcohol consumption. No consistent association of hypertension with gender and educational attainment was observed across populations, and no association was observed with current smoking. Multiple logistic regression analyses using waist circumference instead of BMI did not result in a higher degree of association with the prevalence of hypertension (data not shown).
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A multiple logistic regression analysis with the combined data of all 4 populations was used to evaluate additional population-related risk associated with hypertension prevalence (Table 3). Alcohol consumption was treated as a categorical variable (0, 0.1 to 13.9, and 14 drinks/wk), because its association with hypertension followed a J-shape pattern in both men and women (data not shown). Current smoking was not introduced because of its lack of association with hypertension prevalence in each one of the populations. Relative to SA-NHWs, an excess prevalence of hypertension was demonstrated in Spain (OR, 1.53; 95% confidence interval [95% CI], 1.24 to 1.90). A lower hypertension prevalence was statistically significant in Mexico (OR, 0.67; 95% CI, 0.53 to 0.85) and close to significance in SA-MAs (OR, 0.86; 95% CI, 0.71 to 1.03). Compared with no alcohol consumption, alcohol intake of 0.1 to 13.9 drinks/wk was associated with lower prevalence of hypertension (OR, 0.85; 95% CI, 0.74 to 0.97); alcohol intake 14 drinks/wk, with higher prevalence (OR, 1.41; 95% CI, 1.15 to 1.72).
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Discussion |
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Blood pressure values and the prevalence of hypertension are significantly higher in Spain than in San Antonio and Mexico City. Comparable blood pressure results have been reported in Spain16–18 and have been associated with the relatively high cerebrovascular mortality in Spaniards, which is twice as high as in US citizens.19
The increased risk for hypertension associated with age, BMI, and glucose tolerance is well established, but it is remarkable that this risk is increased similarly in populations that have different genetic, socioeconomic, and cultural backgrounds. We have previously shown that waist circumference is the best obesity-related predictor of type 2 diabetes in Mexican-origin populations.20 However, waist circumference is not better than BMI for its association with the prevalence of hypertension. In our analyses, we have used BMI as the index of obesity because of the high correlation between BMI and waist circumference and the availability of BMI in clinical practice. In a previous report from the SAHS, we observed no association between fasting glucose and the incidence of hypertension in nondiabetic subjects.9 But in this larger current analysis, the prevalence of hypertension is associated with IGT as much as it is associated with type 2 diabetes in all 4 populations. Thus, metabolic changes responsible for hypertension are already present in subjects with IGT. In this regard, we have already reported that the incidence of hypertension is directly related to fasting insulin (a surrogate for insulin resistance) and insulin secretion in Hispanic and non-Hispanic whites.9
Although hypertension prevalence is lower in women age 35 to 44 years than in age-matched controls, no association is observed between hypertension prevalence and gender in any of the populations. Alcohol consumption is associated with age, gender, and indices of obesity, but the relationship between alcohol and prevalence of hypertension is independent of those variables. Some epidemiological studies have reported cardiovascular benefit with alcohol intakes beyond the amount of 14 drinks/wk.21,22 This is a subject of debate that needs further clarification by prospective studies. However, our data indicate that a higher prevalence of hypertension is associated with alcohol consumption 14 drinks/wk. Thus, alcohol consumption may be of epidemiological importance in Spain because alcohol consumption 14 drinks/wk is observed in 32% of Spanish men. Of interest is also the similar or even lower prevalence of hypertension in subjects with alcohol consumption between 0.1 and 13.9 drinks/wk than in those without alcohol consumption, although statistical significance is observed only in the combined analysis of all 4 populations.
We have previously described an inverse association between educational attainment and the prevalence of hypertension in San Antonio and Mexico City. However, a multiple logistic regression analysis demonstrated that this association was statistically significant in Mexican and Mexican American men but not in women, and only when the level of educational attainment was dichotomized to 8 versus <8 years of education.11 In this present analysis, we observe an independent association between educational attainment 12 years and hypertension prevalence only in Spain, which may be responsible for the statistical significance of educational attainment in the combined analysis of all 4 populations. However, this finding is not free from caveats. Similar levels of education may have different health consequences in populations that differ in their socioeconomic status and cultural background. The statistical power of our analysis may be undermined by the high school completion rates, which were very low in Mexico and Spain and very high in SA-NHWs. Neither are these studies suitable for comparisons regarding other factors related to education, culture, and socioeconomic level, such as salt intake, saturated fat consumption, and level of exercise.23,24 Of particular interest is salt consumption because some epidemiological surveys have observed a very high daily intake of salt in Spain.25
In summary, the prevalence of hypertension is similarly associated with age, BMI, glucose tolerance, and alcohol consumption in all 4 populations. In Spanish men, alcohol consumption is particularly high, which may partially contribute to their high prevalence of hypertension. Differences in education, BMI, glucose tolerance, and alcohol consumption do not fully explain the increased prevalence of hypertension in Spain and the lower prevalence in Mexican-origin populations. Although we cannot conclude definitively that these differences are genetically driven, these results suggest no relationship between Spanish genetic admixture and the deficit in hypertension prevalence in Mexican-origin populations.
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Acknowledgments |
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Spanish Insulin Resistance Study Group (SIRSG) Principal Investigators are Rafael Gabriel, MD (Hospital de la Princesa de Madrid), and Manuel Serrano-Ríos, MD (Hospital Clínico de San Carlos de Madrid). SIRSG Associated Investigators Juan Cabello-López, MD (Hospital Universitario de Alicante), Isabel Esteva, MD (Hospital Civil de Málaga), José M Fernández-Carreira, MD (Hospital San Agustín de Avilés), Pedro Horcajo-Aranda, MD (Hospital General Universitario de Guadalajara), María Teresa Martínez-Larrad, MD (Hospital Clínico de San Carlos de Madrid), Javier Muñiz, MD (Hospital de La Coruña), Manel Pladevall-Vila, MD (Hospital General de Vic), Pedro Saenz de Aranzubia, MD (Hospital de Mérida), Antonio Segura-Fragosa, MD (Hospital de Talavera), Federico Soriguer-Escofet, MD (Hospital Civil de Málaga), Saturio Vega-Quiroga, MD (Hospital de Arévalo), and Juan A. Gómez Gerique, MD, PhD, and Amelia Porres, PhD (Fundación Jiménez Díaz de Madrid, Laboratorio de Bioquímica Clínica). This work has been supported by grants from the Fondo de Investigaciones Sanitarias of Spain (FISS 95/0029–02), by the National Heart, Lung and Blood Institute (RO1-HL24799 and R01-HL36820), and by the Fundación Mexicana para la Salud. We thank Milagros Pérez Barba for technical assistance with the biochemical assays.
Received August 23, 2001; first decision November 19, 2001; accepted November 19, 2001.
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