Trends in the Prevalence of Low Risk Factor Burden for Cardiovascular Disease Among United States Adults
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Abstract
Background— Cohorts consistently show that individuals with low levels of cardiovascular risk factors experience low rates of subsequent cardiovascular events. Our objective was to examine the prevalence and trends in low risk factor burden for cardiovascular disease among adults in the US population.
Methods and Results— We used data from adults 25 to 74 years of age who participated in 4 national surveys. We created an index of low risk from the following variables: not currently smoking, total cholesterol <5.17 mmol/L (<200 mg/dL) and not using cholesterol-lowering medications, systolic blood pressure <120 mm Hg and diastolic blood pressure <80 mm Hg and not using antihypertensive medications, body mass index <25 kg/m2, and not having been previously diagnosed with diabetes mellitus. The age-adjusted prevalence of low risk factor burden increased from 4.4% during 1971 to 1975 to 10.5% during 1988 to 1994 before decreasing to 7.5% during 1999 to 2004 (P for nonlinear trend <0.001). The patterns were similar for men and women, although the prevalence among women exceeded that among men in each survey (P<0.001 for each survey). In addition, whites had a significantly higher prevalence of low risk factor burden than blacks during each survey except during 1976 to 1980 (1971 to 1975, 1988 to 1994, 1999 to 2004: P<0.001; 1976 to 1980: P=0.154). Furthermore, a larger percentage of whites had a low risk factor burden than Mexican Americans during 1988 to 1994 (P<0.001) and 1999 to 2004 (P=0.001).
Conclusions— The prevalence of low risk factor burden for cardiovascular disease is low. The progress that had been made during the 1970s and 1980s reversed in recent decades.
Received November 14, 2008; accepted July 2, 2009.
Cardiovascular diseases continue to exact a heavy price in the United States. In 2005, ≈650 000 deaths were attributed to heart disease and ≈140 000 deaths to stroke.1 Furthermore, ≈16.8 million adults were living with coronary heart disease and 6.5 million with stroke in 2006.2 In addition, the direct and indirect economic costs attributable to coronary heart disease and stroke for 2009 are estimated at $234 billion.2
Editorial see p 1171
Clinical Perspective on p 1188
Most premature cardiovascular disease is preventable. Furthermore, coronary heart disease mortality in the United States halved between 1980 and 2000; ≈44% of this decrease was attributable to changes in major risk factors.3 A large body of research has shown that smoking, hypertension, hypercholesterolemia, diabetes mellitus, sedentary behavior, poor nutritional practices, and excess weight increase the risk of developing cardiovascular disease.4,5 Conversely, a growing number of studies demonstrate that people with a low burden of risk factors have a substantially reduced risk of developing cardiovascular disease.6–16 In addition, people without risk factors were also shown to incur lower Medicare costs than those with risk factors.17 Furthermore, modest but feasible reductions in major risk factors might halve coronary heart disease deaths in the United Kingdom and possibly the United States.18
Knowing the prevalence of low risk factor burden is crucial in understanding how much progress in reducing the incidence and mortality from cardiovascular disease remains to be potentially achieved. Because recent national estimates of low risk factor burden are not available and its trends have not been investigated, we examined these issues using data from national studies conducted in the United States.
Methods
Study Population
We used data from National Health and Nutrition Examination Survey (NHANES) I (1971 to 1975), NHANES II (1976 to 1980), NHANES III (1988 to 1994), and NHANES 1999 to 2004.19–24 Participants were selected by use of a stratified multistage probability sample design. After an interview in their home, participants were invited for an examination in the mobile examination center, where they were asked to complete additional questionnaires, to undergo various examinations, and to provide a blood sample. With the use of sampling weights, each survey yields estimates that are representative of the noninstitutionalized, civilian US population.
Low Risk Factor Burden
Using a previous definition of low risk factor burden,8 we created an index of low risk from the following variables: not currently smoking, total cholesterol <5.17 mmol/L (<200 mg/dL) and not using cholesterol-lowering medications, systolic blood pressure <120 mm Hg and diastolic blood pressure <80 mm Hg and not using antihypertensive medications, body mass index <25 kg/m2, and not having been previously diagnosed with diabetes. Each favorable factor was assigned a value of 1, and the presence of its unfavorable counterpart was given a value of 0. The sum of the scores for the 5 factors was then dichotomized, with a value of 5 representing low risk and the other scores representing increased risk.
Measurements
Not currently smoking was defined as not having smoked 100 cigarettes during a participant’s lifetime or as having smoked 100 cigarettes, but not at the time of the interview. Favorable total cholesterol status was defined as a concentration of total cholesterol <5.17 mmol/L and not using cholesterol-lowering medications based on self-report. Details about measurements of total cholesterol have been published elsewhere.25 Low blood pressure was defined as a systolic blood pressure <120 mm Hg and a diastolic blood pressure <80 mm Hg and not currently using antihypertensive medication based on self-report. Details about blood pressure measurements can be found elsewhere.26–28 Body mass index (kg/m2) was calculated from measured height and weight. A low risk body mass index was defined as a body mass index <25 kg/m2. Not having been diagnosed with diabetes mellitus by a physician was based on self-report.
Statistical Analysis
We limited the analyses of the surveys to men and nonpregnant women 25 to 74 years of age who attended the medical examination. The analytic sample sizes for low risk factor burden were 6614 for NHANES I, 10 369 for NHANES II, 11 703 for NHANES III, and 9358 for NHANES 1999 to 2004. We examined trends in the prevalence of low risk factor burden and its components among 3 age groups (25 to 44, 45 to 64, and 65 to 74 years), among men and women, and among whites, blacks, and Mexican Americans (for NHANES III and NHANES 1999 to 2004 only). When age adjustment was performed, we directly adjusted to the US projected population 25 to 74 years of age in the year 2000. Linear trend was assessed by use of a time variable corresponding to the approximate midpoint of the surveys in log-binomial regression models after adjustment for age (except age-specific models), sex (except sex-specific models), ethnicity (except for ethnicity-specific models), and educational status (less than high school, high school graduate, more than high school). Nonlinear trend was assessed by adding a squared time variable to the models. Differences in prevalence estimates were tested with the χ2 test. We used SUDAAN (Software for the Statistical Analysis of Correlated Data) for analyses to account for the complex sampling design and used sampling weights calculated for participants who attended the mobile examination center.
Results
Mean age remained relatively steady during the period covered by the surveys (P for linear trend=0.502; Table 1). However, the percentage of men (P for linear trend=0.003) and high school graduates increased (P for linear trend <0.001), and the percentage of participants who were white decreased (P for linear trend <0.001).
Table 1. Unadjusted Demographic Characteristics of US Adults 25 to 74 Years of Age Who Participated in 4 National Surveys
The age-adjusted prevalence of low risk factor burden increased from 4.4% during NHANES I (1971 to 1975) to 10.5% in NHANES III (1988 to 1994) before decreasing to 7.5% in NHANES 1999 to 2004 (P for nonlinear trend <0.001) (Figure 1). The patterns were similar for men and women, although the prevalence among women exceeded that among men in each survey (P<0.001 for each survey). The prevalence of low risk factor burden was much higher among participants 25 to 44 years of age than among those 45 to 64 or 65 to 74 years of age (P<0.001 for each survey). In addition, whites had a significantly higher prevalence of low risk factor burden than blacks during each survey except during NHANES II (NHANES I, III, and 1999 to 2004: P<0.001; NHANES II: P=0.154). Furthermore, a larger percentage of whites had a low risk factor burden than Mexican Americans in NHANES III (P<0.001) and NHANES 1999 to 2004 (P=0.001). In a separate analysis, we defined favorable total cholesterol and blood pressure status using only the measured values of these variables. Thus, treatment with medications to lower total cholesterol or blood pressure was not used in determining risk status. The resulting estimates of the age-adjusted prevalence of low risk factor burden for the 4 periods were 4.4%, 6.2%, 10.7%, and 7.9%.
Figure 1. Trends in the age-adjusted prevalence (95% confidence interval) of low risk factor burden for cardiovascular disease among US adults 25 to 74 years of age.
The nonlinear trend of the index reflecting low risk factor burden comprised 5 factors that did not move uniformly in time (Table 2⇓). Thus, the trend of participants who reported not having been diagnosed with diabetes decreased linearly (P<0.001), whereas the temporal changes in the other low risk factors exhibited a nonlinear component (Table 2⇓). The directions of the trends for the individual risk factors were generally similar for the demographic groups. We also calculated the prevalence of favorable blood pressure status by assigning participants to low risk status using only the measurements of systolic and diastolic blood pressures (treatment with antihypertensive medications was not used in determining risk status). The age-adjusted estimates for the 4 time periods were 21.6%, 28.8%, 48.9%, and 43.7%, respectively. In addition, we calculated the prevalence of favorable total cholesterol status by assigning participants to low risk status using only the measurements of total cholesterol (treatment with cholesterol-lowering medications was not used in determining risk status). The age-adjusted estimates for the 4 time periods were 34.5%, 37.9%, 45%, and 48%, respectively. Additional details for trends in categories of blood pressure, total cholesterol, and body mass index are shown in Figure 2.
Table 2. Age-Adjusted* and Age-Specific Prevalence of the 5 Components of Low Risk Factor Burden for Cardiovascular Disease Among US Adults 25 to 74 Years of Age
Table 2. Continued
Figure 2. Trends in the age-adjusted prevalence of categories of total cholesterol (mmol/L) among adults not using cholesterol-lowering medications (A), blood pressure among adults not using antihypertensive medication (B), and body mass index (kg/m2) among all adults (C).
In a study conducted among young women,8 participants who did not meet the criteria for low risk and did not have a single elevated risk factor (systolic blood pressure ≥140 mm Hg or diastolic blood pressure ≥90 mm Hg or current use of antihypertensive medications, total cholesterol ≥6.21 mmol/L [240 mg/dL] or current use of cholesterol-lowering medications, body mass index ≥30 kg/m2, diabetes, and currently smoking) had a risk for all-cause mortality similar to that for women in the low risk group. The prevalence for this group was 18.9% in NHANES I, 19.3% in NHANES II, 23.3% in NHANES III, and 23.8% in NHANES 1999 to 2004 (P for linear trend=0.003).
Discussion
Our results showed that only ≈8% or 1 in 12 US adults had a low risk profile for cardiovascular disease during 1999 to 2004. This emphasizes the huge potential for preventing cardiovascular disease that remains to be realized. Favorable trends were observed for not currently smoking and low concentrations of total cholesterol, 2 areas that have benefitted from decades-long public health initiatives.29–31 Blood pressure, which was also the beneficiary of a major public health initiative,32 moved in an encouraging direction during the 1970s and 1980s but subsequently changed course, partly as a result of the epidemic of obesity. The prevalence of low risk factor burden for the period 1999 to 2004 was higher than it was for the period 1971 to 1975. However, it had decreased since 1988 to 1994, which is worrisome. Adverse trends in 3 factors contributed to this unfortunate turn of events: not having diagnosed diabetes mellitus, body mass index <25 kg/m2, and favorable blood pressure.
In keeping with a published definition of low risk factor burden,8 we classified participants who used medications to lower blood pressure and total cholesterol as not being at low risk for these 2 risk factors. However, medications can lower values of blood pressure and total cholesterol into the low risk range. Consequently, how medication use is handled in assigning risk status can potentially affect the results. In contrast to our main analysis in Table 2⇑ showing a small nonsignificant decrease in favorable total cholesterol status from NHANES III to NHANES 1999 to 2004, the secondary analysis based strictly on concentrations of total cholesterol found a significantly increasing percentage of adults having a favorable total cholesterol status.
Primordial prevention holds enormous promise in decreasing the burden of cardiovascular disease. A series of studies have demonstrated large risk reductions in cardiovascular disease among participants who had a low risk factor burden.6–8,11–16 At least 2 general approaches to defining low risk were taken in these studies. One combined lifestyle behaviors with physiological and anthropometric factors. The other focused on lifestyle behaviors and included an anthropometric variable.
Previous studies have yielded estimates of the prevalence of low risk factor burden (based on lifestyle behaviors and physiological and anthropometric measures) ranging from ≈4% to ≈20%.6,8,17 Studies that defined low risk factor burden on the basis of lifestyle factors and an anthropometric measure have produced lower estimates ranging from ≈3% to ≈8.5%.7,11,12,14,16,33,34 In comparison, our estimate of the prevalence of low risk factor burden for the period of 1999 to 2004 was 7.5%. Our finding showing that a larger percentage of women have a favorable risk factor profile than men is consistent with most other studies.14,33,34 However, a gender difference was not present in the data from the Chicago Heart Association Detection Project.17 Furthermore, our finding that whites have a more favorable risk factor profile than blacks or Hispanics is also consistent with previous research.14,33,34
Our results suggest that the distribution of total cholesterol progressively improved over time albeit at a less vigorous pace during the most recent period, that the distribution of blood pressure after improving during the first 3 time periods shifted in an unfavorable direction during the most recent period, and that the distribution of body mass index progressively deteriorated over time. These trends argue for vigorous population-based approaches to reverse the unhealthy shift in the distributions of blood pressure and body mass index and to sustain or accelerate the improvement in the distribution of total cholesterol.
Because a high percentage of US adults are in contact with a healthcare provider each year, the healthcare provider is uniquely situated to evaluate the risk factor profile for cardiovascular disease of each patient and, when necessary, to manage their patients through counseling, pharmacological management, and referral. Our results clearly demonstrate a great need for prevention; thus, healthcare providers should have adequate resources, time, and reimbursement to engage in the prevention of cardiovascular disease in individuals. Such efforts by clinicians need to be complemented by efforts by state and national agencies that have the responsibility to develop effective public health interventions. Potential targets for such interventions include work sites and schools where large numbers of people can be targeted and where evidence-based interventions can be implemented.
The impact of the adverse trend of low risk factor burden on the future incidence of and mortality from cardiovascular disease in the United States is difficult to predict because the impact depends on a delicate balance of the direction of the trends of the 5 components, the magnitude of the changes, and the degree that they increase risk. Furthermore, the trends in other risk factors such as physical activity that were not included in this study are also critical to predicting future trends in the incidence of and mortality from cardiovascular disease. In addition, the percentage of the other group of adults who were at low risk for cardiovascular disease mortality (those who did not meet the criteria for low risk and did not have a single elevated risk factor) increased by an absolute 4.6% during the study period, although the increase between NHANES III and NHANES 1999 to 2004 was only 0.6%. The growth of this group potentially offset some of the increase in risk imparted by the shrinking percentage of adults with low risk factor burden.
Our results should be interpreted in light of several limitations. NHANES only surveyed noninstitutionalized adults, so the true levels may be even worse. Furthermore, several definitions of low risk have included physical activity. Because physical activity was assessed completely differently in the various NHANES, we were unable to incorporate it into our analyses. Because dietary intake was assessed with a single 24-hour dietary recall in some of the surveys, deriving a suitable dietary index was also not feasible. Furthermore, the wording of questions for use of current antihypertensive medication and for physician-diagnosed diabetes changed over time. It is unclear whether these changes in wording affected our estimates. In addition, the protocol for measuring blood pressure changed from NHANES I to NHANES III.26 Like other authors, we weighted the factors of our low risk factor burden index equally. Given that our index and those of others were not designed for risk estimation but were constructed to reflect the status of multiple prevention goals that are all supported by government and professional organizations, equal weighting of the individual factors seemed reasonable. If nonresponders to the survey were more likely to be in poor health, it is possible that our estimates of low risk were overestimated.
Healthy People 2010 objectives for adults call for the following targets: smoking prevalence of 12%, hypertension prevalence of 16%, mean concentration of total cholesterol of 199 mg/dL, rate of clinically diagnosed diabetes mellitus of 2.5%, proportion of adults who are at a healthy weight of 60%, and an obesity prevalence of 15%.35 Our analysis suggests that achieving low risk status for most US adults remains a distant and challenging goal. Unfortunately, the limited strides that were made toward this goal during the 1970s and 1980s were eroded by the increases in excess weight, diabetes mellitus, and hypertension during more recent decades. Because prevention offers potentially great opportunities for lessening the burden of cardiovascular disease, it is critical that the percentages of US adults who have optimal blood pressure, who have never developed diabetes mellitus, and who have optimal body weight be improved.
Acknowledgments
Disclosures
None.
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CLINICAL PERSPECTIVE
Smoking, hypercholesterolemia, hypertension, obesity, and diabetes mellitus are risk factors for cardiovascular disease. Major public health campaigns that led to reductions in smoking, reductions in concentrations of total cholesterol, and for a time reductions in hypertension have contributed to large decreases in mortality from cardiovascular disease. In more recent years, the concept of low risk factor burden, which shifts the perspective from risk factor control to primordial prevention of cardiovascular disease, has gained traction. A series of studies has shown that people, who do not smoke or have never smoked, have normal concentrations of total cholesterol and do not use cholesterol-lowering medications, have a systolic blood pressure <120 mm Hg and a diastolic blood pressure <80 mm Hg and do not use antihypertensive medications, have a body mass index <25 kg/m2 and do not have diabetes mellitus, have a greatly reduced risk of developing cardiovascular disease in a dose-dependent fashion. In our study, we show that the age-adjusted prevalence of low risk factor burden during 1999 to 2004 was 7.5% among US adults and that this percentage had decreased from 10.5% during 1988 to 1994. Adverse trends in the percentage of adults having a body mass index <25 kg/m2, diagnosed with diabetes mellitus, and favorable blood pressure drove this change. By emphasizing primordial prevention, public health professionals and clinicians can complement each other’s efforts in helping US adults achieve optimal cardiovascular health.
Footnotes
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The findings and conclusions in this article are those of the authors and do not represent the official position of the Centers for Disease Control and Prevention.
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The online-only Data Supplement is available with this article at http://circ.ahajournals.org/cgi/content/full/CIRCULATIONAHA.108.835728/DC1.
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- Trends in the Prevalence of Low Risk Factor Burden for Cardiovascular Disease Among United States AdultsEarl S. Ford, Chaoyang Li, Guixiang Zhao, William S. Pearson and Simon CapewellCirculation. 2009;120:1181-1188, originally published September 28, 2009https://doi.org/10.1161/CIRCULATIONAHA.108.835728
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- Trends in the Prevalence of Low Risk Factor Burden for Cardiovascular Disease Among United States AdultsEarl S. Ford, Chaoyang Li, Guixiang Zhao, William S. Pearson and Simon CapewellCirculation. 2009;120:1181-1188, originally published September 28, 2009https://doi.org/10.1161/CIRCULATIONAHA.108.835728