The etiology of hypertension remains unknown, but one fact is clearly established: no single cause is responsible. High blood pressure is the end result of a number of factors, both genetic and environmental, which may be quantitatively and qualitatively different in different individuals. It has for many years been suspected that an adverse reaction between an individual and his or her environment may play a role in the development of hypertension, although conclusive evidence is still lacking. Four general approaches have been used to identify the potential role of such factors. The first is to study the effects of environmental stressors in epidemiological studies, the second is to look for personality differences between normotensive and hypertensive individuals, the third is to examine the relevance of individual differences in susceptibility or reactivity to standardized stressors in a laboratory setting, and the fourth is animal studies.
In man, there is abundant evidence for the influence of social and cultural effects on blood pressure, as shown by studies of people who migrate from a traditional society to a westernized one, and experience an increase of blood pressure. Another factor that is associated with higher blood pressure is "lifestyle incongruity," whereby people's expenditures exceed their incomes. Some of the most convincing evidence comes from studies of job strain, a measure of occupational stress which has been related not only to coronary heart disease, but also to hypertension in both cross sectional and prospective studies. Men employed in high strain jobs (defined by low control and high demands) have increased ambulatory blood pressure and greater left ventricular mass, but the same does not apply in women. Studies of personality have not been very successful at identifying a hypertensive personality, but both anxiety and depression have been found to predict future hypertension. Physiological differences in blood pressure reactivity have generally given inconclusive results. Animal studies have shown that stressful social interactions can lead to a sustained increase of blood pressure, but only in susceptible genetic strains of animals.
One of the most interesting questions concerns the higher prevalence of hypertension in African Americans as compared to whites. Hypertension is relatively rare in rural Africa, but becomes more prevalent in urban migrants, suggesting environmental rather than genetic origins. Studies done in the U.S. have shown that blood pressure tends to be higher in disadvantaged neighborhoods. The racial differences in the prevalence of hypertension may be partly due to differences in socioeconomic status.
It will be argued that chronic environmental stress can have effects on blood pressure which are equivalent in magnitude to those of aging and obesity.
The implications for the prevention of hypertension remain to be determined. Change in body weight is one of the most potent predictors of blood pressure change, and there is evidence that central obesity may be in part the result of exposure to chronic stress. Control of hypertension is a major unresolved problem, and the same psychological factors that promote the development of hypertension (especially depression) may also lead to poor adherence to treatment.
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