Hypertension is not an equal opportunity disorder. That is, it affects persons with certain demographic characteristics more than persons without those characteristics. For example, there is a linear relation between blood pressure and age, and it is well known that hypertension proportionately affects persons of African ethnicity more than those of Caucasian ethnicity.
Incidence of essential hypertension is actually slightly lower among Mexican Americans despite the increased prevalence of obesity and diabetes among them (Fields et al., 2004; Sorel, Ragland, and Syme, 1991).
As depicted in Figure 1.3, prevalence rates increase with age, but this change is affected by both sex and race. During early adulthood, males have higher rates of hypertension than females, particularly among African Americans. However, in middle adulthood, prevalence rates for female African Americans rise above male African American rates, while males continue to have higher prevalence than females among Caucasian Americans. Finally, in older adulthood, females of both races have higher prevalence rates than males. Regardless of sex or race, however, it is easy to conclude that a significant number of Americans, particularly older Americans, can be diagnosed with high blood pressure. In the United States nearly one out of every three adults has high blood pressure (Fields et al., 2004). Estimates of high blood pressure are even higher in some other industrialized countries. For example, in Germany, Finland, and Spain roughly 44 percent of the adult population can be diagnosed with hypertension (Wolf-Maier et al., 2003), and in Japan the estimated prevalence of high blood pressure is as high as 73 percent among older adults (Curb et al., 1996).
Regardless of prevalence differences pertaining to race or age, it is quite evident that hypertension is a very common medical problem. In fact, it is the most common primary diagnosis assigned during outpatient visits in the United States with over 35 million office visits to medical clinics annually (Cherry and Woodwell, 2002).
Figure 1.3. Prevalence of high blood pressure in Americans by age, sex, and race. Adapted from M. Wolz et al., Statement from the National High Blood Pressure Education Program: Prevalence of hypertension, American Journal of Hypertension, 13, pp. 103-104.
Furthermore, data from the National Health and Nutrition Examination Surveys
) have revealed that about 30 percent of hypertensive patients in the community were not aware they had high blood pressure, and were therefore not receiving treatment (Burt et al., 1995). Of those community-dwelling adults who were being treated, only about a third of them had achieved good control of their hypertension with treatment.
Although some gradual improvement has been noted in identifying and treating hypertension over the past few decades, the condition still represents a significant medical problem for a large number of people.
It is generally acknowledged that there is a genetic component to the development of essential hypertension (Pickering and Sleight, 1977). Individuals with hypertensive parents possess a much higher risk for developing hypertension themselves than individuals of normotensive parentage (Paffenbarger, Thorne, and Wing, 1968; Zinner, Levy, and Kass, 1971). Transmission is considered polygenic, as there is no evidence that any single gene could regulate each of the interrelated systems that affect blood pressure. Although genetics certainly contributes to determining the risk for essential hypertension, it is clear that environmental factors also need to be considered when predicting who will develop the disorder. To illustrate the interaction between genetic and environmental contributions, consider the classic work of Dahl, Heine, and Tassinari (1962), who demonstrated that elevations in blood pressure occurred among certain strains of rats only when exposed to conditions of salt loading. Despite the importance of hereditary factors, there are plenty of individuals who develop hypertension with no known genetic propensity for the disorder, as there are individuals who live out their lives with normal blood pressure despite having a strong family history of hypertension.
A few additional demographic or personal characteristics increase risk for developing hypertension, including concurrent diagnoses of diabetes mellitus, the presence of obesity, physical inactivity, and excessive use of sodium and alcohol (Page, 1983). The relative contribution for each of these characteristics is uncertain, however, because there is considerable overlap among them. For example, among the substantial number of obese patients who are diagnosed with diabetes, it is unclear whether the risk of hypertension is associated with the diabetic condition, obesity, or both diabetes and obesity.