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Hypertension is a condition that can claim a number of firsts: It is the most common chronic condition in the United States; it is the number one reason for an office visit to a physician; it accounts for the most drug prescriptions; it is a major risk factor for heart disease and stroke, which are the first and third leading causes of death in the United States; and it is the number one attributable risk for death throughout the world.1 At the same time, it is both preventable and treatable in the majority of patients. Despite these impressive statistics, hypertension continues to be neglected. It is not recognized as a condition worthy of specialist care, and only approximately one-third of hypertensive patients in the United States have their blood pressure controlled to target levels that have been proven in numerous studies to reduce the rates of heart attacks and strokes. In addition, although the death rates from these two conditions have been decreasing over the past 20 years, the rates of two others that are also consequences of hypertension—heart failure and chronic kidney disease—have been increasing. It gets worse yet: A major public health concern in the United States today is the epidemic of obesity, which has resulted in a major increase in the prevalence of type 2 diabetes and which increases the risk of cardiovascular events to the same degree as a prior myocardial infarction, for which the most effective treatment is the aggressive reduction of blood pressure. So perhaps the worst single statistic relating to hypertension is that less than 25% of patients with diabetes have their blood pressure adequately controlled.

This chapter reviews the epidemiology of hypertension—what it is and how it is classified; how common it is; who is affected by it; its consequences, and how they are affected by treatment; and the degree to which it is being controlled.

There is agreement that hypertension is a quantitative rather than a qualitative disease. The basis for this statement rests on a large number of epidemiologic studies showing that the distribution of blood pressure in the population is continuous, although the curve is skewed at the higher levels of blood pressure. This was not always accepted: In the 1950s there was a sharp debate between Sir George Pickering and Lord Robert Platt that played out in the correspondence section of the Lancet and was subsequently assembled in a monograph.2 Pickering took the view that the distribution of blood pressure in the population is continuous and that there is no discernible separation between subjects with high blood pressure from those with normal blood pressure. Platt had data that indicated that there was a bimodal distribution and that a hypertensive subpopulation could be distinguished from the normotensive majority, a dispute that could be summarized as "one hump or two?" The general consensus was that Pickering won and that the unimodal distribution holds sway. This has important implications, first ...

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