Trends in Hypertension Prevalence, Awareness, Treatment, and Control Rates in United States Adults Between 1988–1994 and 1999–2004

Hypertension, or high blood pressure (HBP), is the most important cardiovascular risk factor worldwide, contributing to one half of the coronary heart disease and approximately two thirds of the cerebrovascular disease burdens.¹ In the United States, the estimated prevalence of hypertension (defined as systolic blood pressure [BP] ≥140 mm Hg and/or diastolic BP ≥90 mm Hg and/or receiving antihypertensive medication) derived from the 1988–1994 Third National Health and Nutrition Examination Survey (NHANES III) was 42 million adults. An additional 8 million Americans reported having been told twice by a health professional that they have HBP, but their BP was <140/90 mm Hg at the NHANES III examination.^2–4 This subgroup, termed “twice told,” increased the hypertension prevalence estimate to 50 million persons. In 1999–2000, prevalence was estimated as 59 million among US adults.⁴ There were an additional 6 million persons twice told, yielding a total estimate of 65 million persons based on the NHANES 1999–2000 data.⁴

Since the 1960s, national examination surveys (including NHANES) conducted by the National Center for Health Statistics have been the principal means to track progress in preventing, treating, and controlling hypertension and have been benchmarks for the National High Blood Pressure Education Program and related health objectives for the nation.^5,6 These data have generally indicated favorable trends, ie, improvements in hypertension prevalence, awareness, treatment, and control rates. Except for prevalence, these trends persisted through 1999–2000. There was an 8.3% relative increase in the prevalence rate during the 1990s, partially attributable to the epidemic of overweight and obesity occurring in the United States during the past 2 decades.⁷

In addition to articles describing hypertension trends through the year 2000,^4,7 there have been several other reports using more recent NHANES data. A National Center for Health Statistics data brief updated the overall trends in hypertension through 2006 but did not address trends in awareness, treatment, and control and did not address changes in BP distributions or mean values.⁸ A report by Ostchega et al⁹ analyzed trends through 2004 but only in older persons and without the level of detail in this report. A recent publication by Gu et al¹⁰ investigated data through 2004 but was focused primarily on hypertension treatment patterns. This current report adds to these previous findings through a detailed analysis of NHANES 1999–2004 related to trends in prevalence; trends in awareness, treatment, and control; evaluation of the role of changes in body mass index (BMI) in the changes in hypertension prevalence; and analysis of changes in the mean values and distributions of BP values.

Methods

Data from the NHANES are used to assess the health and nutritional status of the civilian, noninstitutionalized US population. A nationally representative sample is obtained using a complex, stratified, multistage probability cluster sampling design. Selected subpopulations are oversampled, thereby providing a larger subsample size to yield more reliable estimates for these groups. The data used in this article are from NHANES III (1988–1994) and NHANES 1999–2004. Informed consent was obtained from all of the participants, and the protocol was approved by the institutional review board of the National Center for Health Statistics.

NHANES data were collected through a standardized household interview with additional interviewing and a physical examination in a mobile examination center. Respondents who were pregnant or for whom no BP data were available were excluded from the analysis. Because of coding changes, pregnant women could not be excluded from the 2003–2004 portion of the data. From previous estimates, this has an insignificant effect and would alter the prevalence of hypertension by approximately one tenth of a percent. In both surveys, the protocol called for 3 BP measurements at the mobile examination center by a physician using a mercury sphygmomanometer after a 5-minute rest. For NHANES III, 99% of the study population had 3 BP measurements; for NHANES 1999–2004, the figure was 91%. The final analytic sample consisted of 16 351 respondents for NHANES III and 14 430 respondents for NHANES 1999–2004, all age ≥18 years. Additional information about overall NHANES methodology and BP measurement is available elsewhere.^11–13

Respondents were defined as having hypertension if their average systolic BP was ≥140 mm Hg, their average diastolic BP was ≥90 mm Hg, or they reported current use of antihypertensive medication. Awareness was defined as hypertensive respondents having been told at least once by a health professional that they had hypertension. Hypertensive adults were included in the treatment category if they reported the use of a prescribed medicine for hypertension. Among hypertensive persons, control was defined as a systolic BP <140 mm Hg and a diastolic BP <90 mm Hg.

BMI was defined as measured weight in kilograms divided by squared height in meters. There were 3 BMI categories: underweight/normal, defined as a BMI <25 kg/m²; overweight, 25 to <30 kg/m²; and obese, ≥30 kg/m². Respondents were grouped into 6 age groups: 18 to 29, 30 to 39, 40 to 49, 50 to 59, 60 to 69, and ≥70 years of age. Respondents were categorized into 4 racial/ethnic groups according to self-reported race and ethnicity: non-Hispanic white (NHW), non-Hispanic black (NHB), Mexican American (MA), and other. Because the “other racial/ethnic” category is a diverse group, separate results for this group are not shown.

SAS for Windows¹⁴ (SAS Institute, Inc) and SUDAAN¹⁵ (Research Triangle Institute) were used for data management and statistical analysis. All of the estimates were weighted according to the inverse probability of being sampled for the examination. Sampling weights provided with the data were also adjusted for person-level nonresponse and a poststratification adjustment to the estimated US population.¹⁶ Age standardization was done using the year 2000 standard¹⁷ and the age groups defined above.

Comparisons of the differences in means and percentages between the 2 surveys were performed using linear contrasts in the SUDAAN descript procedure. Differences between surveys for population distributions among BP categories as defined in the Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure were evaluated using χ² tests. P values <0.05 were considered statistically significant. To examine the effect of BMI on the trends in hypertension, logistic regression models were examined within each racial/ethnic gender subgroup. Each model included age as a continuous variable and the time period of the surveys (1988–1994 or 1999–2004) as a categorical variable. Two sets of models were compared, first without and then with BMI (as a continuous variable). Adjusted odds ratios were calculated using the logistic procedure in SUDAAN. Odds ratios of which the 95% CI did not include unity were considered significant.

Results

Between NHANES III and the NHANES 1999–2004, the age-standardized prevalence rate of hypertension increased from 24.4% to 28.9% (P<0.001), an 18% relative increase (Table 1). Although there were increases in age-standardized prevalence rates in all of the racial/ethnic-by-gender subgroups, increases were greater for women, and the changes in NHW and MA men were not statistically significant. Non-Hispanic white and black women experienced absolute increases of >5%. These represent relative increases of 24% in NHW women and 14% in NHB women. The absolute increases in NHW and NHB men and MA women were similar (3.0% to 3.6%).

Age-specific prevalence rates increased significantly in all of the age groups of NHW women aged ≥40 years but only in those ≥60 among NHW men. Similarly, in both NHB men and women, age-specific prevalence rates increased the most in those ≥60 years of age. In general, age-specific prevalence rates did not increase significantly in MA men and women.

It is important to evaluate the relationship of increased hypertension prevalence rates to the increasing prevalence of overweight/obesity in the US population. The Figure presents age-standardized prevalence rates by racial/ethnic gender subgroups within categories of BMI for the 2 time periods. Although the statistically significant increases between the 2 time periods are predominantly among women with BMI <30 kg/m², there is an observed increase within every BMI strata for all 3 of the racial/ethnic subgroups of women and NHB men.

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Although the Figure shows a graphical representation of the changes in hypertension prevalence after stratification for levels of BMI, an evaluation using statistical modeling is presented in Table 2. A comparison is made of the relative increase in hypertension between the 2 periods, first adjusting for age, which is analogous to comparing age-standardized prevalence rates in Table 1. Note that the age-adjusted ratios in Tables 1 and 2 are not exactly the same, because they perform age-adjustment using different methodology, and Table 2 shows odds ratios and Table 1 shows a ratio of prevalence rates. Table 1 also shows the relative increase between the 2 periods modeled as if there had been no increase in BMI (ie, adjusted for both age and BMI). The relative increase is measured by an odds ratio, because the logistic model is used. For men, the relative increase (odds ratio) in the recent NHANES compared with the earlier was 0.97 in MA men, 1.18 in NHB men, and 1.23 in NHW men. After adjustment for BMI, there was no statistically significant change in hypertension in men (0.87, 1.08, and 1.04, respectively, for the same groups), indicating that the increase in BMI accounted for nearly all of the increase in hypertension in men. For women, there were much larger relative increases in the prevalence of hypertension in the recent NHANES (1.33, 1.42, and 1.59 in MA, NHB, and NHW women, respectively). However, equivalent to results from the Figure, after adjustment for BMI there continued to be large relative increases in the prevalence of hypertension (1.27, 1.29, and 1.44, respectfully), indicating that some of the increases in hypertension in women were attributable to factors other than their increases in BMI in the recent NHANES period.

Table 3 presents time trends in the BP distributions in the untreated US population by Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure categories of BP. The most notable change seen in most race-gender groups was the upward shift in BP values, lowering the percentage in the normal group and increasing the percentage in the prehypertension group. This distribution change did not occur in the MA group. The distribution change also did not occur in those in the top 2 BMI categories but did occur in the lowest BMI group.

Table 4 indicates that, overall, there has been some improvement in awareness of hypertension, from 68.5% to 71.8%. However, this is most clear in NHW men (from 63% to 70%). Overall, awareness in NHB persons has increased as well, from 71% to 76% between the 2 time periods, mainly among the middle-aged group. Awareness rates have not improved for MA or NHW women and remain only 45% in MA men ages 18 to 49 years.

Treatment rates tended to improve in all of the race-gender subgroups, significantly in NHW and NHB men (P<0.001 for each) and in NHB women (P<0.05), although only approximately half as much as in NHB men. Increases in men, except NHW men, were largest in the middle-aged group, whereas improvements in women were largest over age 70 years. MA men continued to have the lowest treatment rates, 40% overall, and only 25% in young men.

Control rates improved overall and tended to improve in all racial/ethnic-gender groups—more among men than women. NHB and NHW men experienced the largest increases between the 2 time periods, and the highest control rate in 1999–2004 was observed in NHW men, who experienced an increase from 22% to 39%. NHB men experienced a relative increase of ≈80%, from 17% to 30%. Significant improvement in control rates in women overall was not been observed, although middle-aged NHB women and older MA women experienced clear increases (each ≈12% absolute change). NHW women had the highest control rate among the racial/ethnic-gender groups in 1988–1994 but did not experience a significant increase. MA men and women continued to experience low control rates, especially among young men (16%) and older women (19%).

Table 5 presents the net results of the changes in terms of mean BP levels. Age-standardized mean systolic BP increased in women, by 3 mm Hg overall, whereas there were significant increases only in nonhypertensive men. In contrast, age-standardized mean diastolic BPs were lower in men in almost all of the subgroups, with an overall decrease of 3 mm Hg. Mean diastolic BP in women remained essentially unchanged between the 2 time periods except in the treated hypertension group.

When the definition of hypertension is expanded to account for those persons possibly obtaining BP reduction from nonpharmacological means (ie, adding those persons with normal BP but twice told that they have hypertension), the age-adjusted prevalence of hypertension becomes 28.8% in NHANES III and 32.6% in NHANES 1999–2004, ≈4% higher for each time period than found in Table 1. The crude prevalence rate of hypertension in 1999–2004 is 32.0%, with the components of the definition being 18.8% defined by elevated BP, 10.2% defined by control of BP from medications, and 3.0% defined by control of BP from other means. Using this expanded definition, of all persons with hypertension in 1999–2004, 74% were aware, 65% were being treated (56% by medications and 9% by other means), and 41% had their HBP under control (32% by medication and 9% by other means).

Discussion

This article updates hypertension-related trends using recent NHANES data for the adult US population. The major observations are as follows: (1) age-standardized hypertension prevalence rates are increasing in general, and there is no subgroup in which they are declining, suggesting that prevention efforts have not been strongly successful; (2) part but not all of the increase in prevalence can be explained by increasing overweight/obesity; (3) awareness, treatment, and control rates continue to improve, so that they are higher than ever reported; (4) among untreated persons, there is a decrease in the proportion with normal BPs and an increase in the prehypertension category; (5) among each race/ethnic group, ≥1 of the foregoing trends are more favorable in men than in women, and the differentials are particularly striking among NHW persons; and (6) although there have been apparent gains in treatment and control among MA persons, their rates (including awareness) remain substantially lower than for other race/ethnic groups.

How to directly measure interventions to prevent chronic diseases continues to be difficult.¹⁸ Effective prevention of the development of hypertension in the US population would be evidenced by a left shift in the BP population distribution curve over time in nonhypertensive persons.^2,5,19–21 The rising prevalence of adults with excess weight over the study time period partly explains why prevention of hypertension among the US adult population has not improved.^22,23 An estimated 65% of US adults had excess weight in 1999–2002 compared with 56% in 1988–1994, and, on average, overweight adults are getting heavier.²⁴ The presence of obesity is strongly associated with the development of hypertension.²⁵ The achievement and maintenance of a more optimal standardized weight using a healthful dietary plan, recommended levels of regular physical activity, and other behavioral approaches are associated with a significant reduction in BP.^6,26

The presence of a similar positive relationship between BMI and hypertension prevalence for each gender/racial/ethnic subpopulation as observed for both time periods of this study is consistent with results of other reports.^27,28 In the present study, increases in BMI accounted for some but not all of the observed increases in hypertension prevalence among adults: inclusion of BMI in the logistic regression model reduced odds ratios associated with the survey period by more than half in NHW and NHB men but much less in women. Trends in obesity prevalence between 1988–1994 and 1999–2000 were similar in men and women among NHW and MA but greater among NHB women than men.²⁹ More recently, obesity or overweight have been increasing more in men than in women.³⁰

Factors other than obesity likely contributed to the increase in hypertension over the study time period, such as improved survival of hypertensive persons because of better treatment. Other potential determinants could include increasing consumption of dietary sodium, the increasingly sedentary lifestyle of the US population (regular physical activity at recommended levels is associated with lower BP), suboptimal levels of health literacy among the general US population (adoption and maintenance of healthful behaviors may be correlated with higher levels of health literacy), lack of early access to health plan coverage or to high-quality preventive healthcare services, and other factors including changes in alcohol and potassium consumption.^31–33 In 1999–2002, 9% to 10% of US adults 18 to 64 years of age had health plan coverage from public sources, and 72% to 75% had private health plan coverage.³⁴ Effective treatment of hypertension significantly reduces the risk of adverse clinical outcomes, including end stage renal disease and morbidity/mortality attributable to myocardial infarction, stroke, and heart failure.^6,35,36

The more favorable overall trend for men compared with women in this study was unexpected in view of a generally greater access to care for women.³⁷ On the other hand, access to care may play a role in recent trends, because in 2002 more women than men did not get medical care (5.2% versus 4.2%) or delayed it because of concerns about cost (7.1% versus 6.0%).³⁷

Subgroup analyses among the race/ethnic subpopulations showed similar men-more-than-women improvement patterns as the overall population, but with women retaining higher rates. Among hypertensive NHB persons, both men (by 14%) and women (by 7%) showed significant improvements in treatment rates (33% and 11% in relative terms, respectively). Whether these outcomes reflect the impact of gender/racial/ethnic-focused efforts or are the result of other factors remains to be determined.³⁸ Although there was a nonsignificant improvement in the treatment and control rates among MA men, their very low awareness, treatment, and control rates demonstrate the need for and use of additional focused efforts in this subpopulation.³⁹

The ultimate clinical practice objective for the management of hypertensive individuals and a very important public health target is the achievement of BP control.⁴⁰ Estimated hypertension control rates improved from 26.0% to 35.0%, a relative increase of 34.5% for the overall US adult population. The overall gender difference in improvement of control rates over the study period is striking and may represent the results of targeted efforts. The 50% relative improvement in the control rate for MAs was significant and consistent with observations for treatment rates, but the persisting low rates underscore the need for additional attention.

The new findings show that men had higher systolic and diastolic BP than women, but the differences were significantly less in 1999–2004 compared with 1988–1994. The observed 2-mm Hg increase in mean systolic BP among the overall US adult population over the study period is primarily attributable to the SBP increase among women. Conversely, mean diastolic BP fell by 1 mm Hg overall because of a statistically significant 3-mm Hg decline in men, whereas there was no significant change in women. The basis for the more favorable overall BP trends for men compared with women may be attributable to the increased percentage who are aware, treated, and controlled in men but not in women.

Qualifications and Limitations

Hypertension prevalence rates reported in this study are for the overall nonpregnant, noninstitutionalized, nonmilitary US population. Accordingly, a potential underestimation bias may exist in view of the fact that a relatively high proportion of adults in nursing homes, hospices, chronic disease hospitals, and other chronic care facilities have hypertension. Although this effect is offset by exclusion of adults likely to have normal BP (eg, many military personnel), the extent of the offset was not estimated.

Estimates are provided that both exclude and briefly include a subpopulation that has been traditionally overlooked: those who were nonhypertensive at the time of the survey but who have been told at least twice that they have hypertension. Exclusion of this subpopulation permits a more direct comparison with previous studies that only evaluated adults who were hypertensive by direct measurement or reported use of antihypertensive medication. Inclusion of this subpopulation who reported previously confirmed hypertension but whose BP was controlled by means other than antihypertensive medication (eg, nonpharmacologic therapy or diminished left ventricular function) is more representative of the overall population.^41,42

Each data collection period occurred over 6 years. This approach ensures a large enough sample size and represents a strength of this study. However, trends occurring within each 6-year period were not evaluated in these analyses.

Although the sample size for the MA subpopulation was smaller than for the other racial/ethnic groups in NHANES III, it was actually larger than for the NHB subpopulation in the 1999–2004 survey. Accordingly, the historical difficulties with achieving large enough sample sizing by oversampling some groups were not as severe as in past studies.

Perspectives

Effective prevention, detection, treatment, and control of HBP continue to be important goals for health policy, public health, and medical care decision makers, as well as advocates and individuals at risk for hypertension.⁴³ A positive impact of their aggregate efforts, interventions, and health behaviors will likely be reflected in improvements in key BP-related trends (or vice versa). For example, hypertension control rates have risen progressively from 1976 to 1980 to 1999 to 2004. However, the same data underscore the fact that there is still much that needs to be accomplished to further improve hypertension control rates for the US population.⁴⁴

The overall hypertension prevalence trend for 1988–1994 to 1999–2004 is upward, driven primarily by a rise among women. This is contrary to the Healthy People 2010 objective that set as a goal to reduce the percentage of hypertension to an overall age-standardized prevalence in adults of 14%.⁴⁵ The fact that rates are rising in the context of progressive rise in age and BMI of the overall population is of particular concern from a public health policy, as well as a medical care perspective. There are important unanswered questions about why the proportion of women with hypertension is rising 2 times faster than for men.

Although important progress continues to be made in the area of awareness, treatment, and control, the need continues to be high for interventions that will ultimately halt and reverse this rising tide of hypertension prevalence. The rapid improvements in BP control in some groups does suggest that the Health People 2010 objective to achieve a goal of 68% under control may have a chance of succeeding, eg, in NHW men. However, the very low control rates in some groups, such as 21% in MA men, indicate continued critical disparities in health care access and implementation. A better understanding of what is impeding further progress in the treatment of hypertension in women, especially NHW women, is needed. To the extent that it reflects a lack of appreciation of the importance of cardiovascular disease in women, progress may be stimulated by campaigns launched since 2003 by the federal government, voluntary agencies, and advocacy groups focusing on raising public and clinician awareness regarding the importance of preventing, detecting, and treating heart disease in women.

Footnotes