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TABLE 20-1 Classification of Blood Pressure in

Adults 18 Years and Oldera

Blood Pressure


Range (mm Hg)





Normal blood pressure


High-normal blood pressure


Mild hypertension


Moderate hypertension

³ 115

Severe hypertension

Systolic, when diastolic

blood pressure is <90


Normal blood pressure


Borderline isolated systolic hypertension

³ 160

Isolated systolic hypertension

a Adapted from JNC (1988). Blood pressures are based on the average of two or more readings on two or more occasions.

b A classification of borderline isolated systolic hypertension (SBP 140-159 mm Hg) or isolated systolic hypertension (SBP ³ 160 mm Hg) takes precedence over a classification of normal diastolic blood pressure (DBP < 85 mm Hg) or high-normal diastolic blood pressure (DBP 8589 mm Hg) when either occurs in the same person. A classification of high-normal diastolic blood pressure (DBP 85-89 mm Hg) takes precedence over a classification of normal systolic blood pressure (SBP < 140 mm Hg) when both occur in the same person.

Population comparisons indicate that there are substantial differences in mean blood pressure values and distributions and in the frequency of adult hypertension that cannot be explained solely by problems of standardization and reliability of measurement. Data derived from the 1976-1980 National Health and Nutrition Examination Survey (NHANES II) conducted by the National Center for Health Statistics (Carroll et al., 1983) indicate that approximately 25 million adults in the United States (17.7%) have definite hypertension according to WHO  criteria and that an additional 17 million  (12.0%) have borderline hypertension (DHHS, 1986). If the JNC IV criteria are used, 42 million adults (29.7%) are hypertensive. Average SBP is higher among blacks than among whites in most adult age groups. Mean DBP is generally higher in men than in women and higher in black adults than in white adults. Isolated systolic hypertension was found to be rare below age 55 (DHHS, 1986).

Comparison of NHANES II data (DHHS, 1986) with those from two previous surveys—one during 1960-1962 (DHEW, 1963) and one during 1971-1975 (DHEW, 1979)—indicates no significant trend in population mean or in distribution of average blood pressure for any ages between the 1960-1962 and 1971-1975 surveys, but NHANES II (1976-1980) showed a lower average SBP at all ages above 30 and a lower overall prevalence of hypertension in people over 40, based on either the WHO or the JNC IV criteria. The relative contributions to this possible lowering of average blood pressure made by detection and control programs and by primary prevention could not be determined from the data. Although both factors have probably played a role, there is no direct evidence of a decline in mean population blood pressure that is independent of medical treatment. Similarly, there is no evidence that the decline in high blood pressure has resulted from a change in the average weight of the population, since this has risen in recent years in the United States.

Additional data on the distribution of hypertension in the population are given in Chapter 5.

Evidence Associating Dietary Factors with Hypertension

Human Studies

The relationships among body mass, obesity, and hypertension have been extensively examined in human populations (see Chapter 21). In virtually every epidemiologic study of blood pressure throughout the world, investigators have found strong correlations between body mass and blood pressure and between obesity and hypertension. Although problems of measurement occur when cuff size is not properly adjusted to arm circumference in obese people, the relationship between body mass and blood pressure remains highly significant, even when this source of error is controlled. Blood pressure and body mass are well correlated in both the hypertensive and the normal ranges.

Weight gain during adult life is associated with increased blood pressure levels. In the Framingham study, the risk of developing hypertension among those normotensive at entry was proportional to subsequent weight gain (Kannel et al., 1967). In general, risk appears greatest in people who gain weight during the third and fourth decades of life, after which the relationship weakens (Oberman et al., 1967; Stamler et al., 1975). Loss of weight by obese hypertensives is associated with a reduction in blood pressure, especially during active weight loss (Chiang et al., 1969; Reisin et al., 1978; Tuck et al., 1981; Tyroler et al., 1975). Little is known, however, about the effects of sustained weight loss

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