Serum Total Cholesterol Concentrations and Awareness, Treatment, and Control of Hypercholesterolemia Among US Adults
Findings From the National Health and Nutrition Examination Survey, 1999 to 2000
Background— Serum cholesterol concentrations have decreased in the US population. Whether the decline continued during the 1990s is unknown.
Methods and Results— We used data from 4148 men and women aged ≥20 years who had a total cholesterol determination or reported using cholesterol-lowering medications and who participated in the National Health and Nutrition Examination Survey (NHANES) from 1999 to 2000 (this is a cross-sectional health examination survey of the US population), and we compared the results with data from 15 719 participants in NHANES III (1988 to 1994). For all adults, the age-adjusted mean total cholesterol concentration decreased from 5.31 mmol/L (205 mg/dL) in NHANES III to 5.27 mmol/L (203 mg/dL) in NHANES 1999 to 2000 (P=0.159). The age-adjusted mean total cholesterol concentration decreased by 0.02 mmol/L (0.7 mg/dL) among men (P=0.605) and 0.06 mmol/L (2.3 mg/dL) among women (P=0.130). Significant decreases were observed among men aged ≥75 years, black men, and Mexican-American women. Among participants who had a total cholesterol concentration ≥5.2 mmol/L (200 mg/dL) or who reported using cholesterol-lowering medications, 69.5% reported having had their cholesterol checked, 35.0% were aware that they had hypercholesterolemia, 12.0% were on treatment, and 5.4% had a total cholesterol concentration <5.2 mmol/L (200 mg/dL) after age adjustment.
Conclusions— The mean serum total cholesterol concentration of the adult US population in 1999 to 2000 has changed little since 1988 to 1994. The low percentage of adults with controlled blood cholesterol concentration suggests the need for a renewed commitment to the prevention, treatment, and control of hypercholesterolemia.
Received November 25, 2002; revision received February 13, 2003; accepted February 18, 2003.
Heart disease is the leading cause of mortality in the United States. In 1999, >12 million people in the United States were estimated to have coronary heart disease, and ≈960 000 died from this disease.1 The economic costs associated with coronary heart disease are estimated to be $112 billion. Thus, the public health burden of this condition is enormous.
Major modifiable risk factors for coronary heart disease include smoking, hypercholesterolemia, hypertension, glucose intolerance, obesity, and physical inactivity. Population campaigns have led to decreases in the prevalence of smoking, hypertension, and cholesterol concentrations.2–4 Although impressive decreases in mean cholesterol concentrations have occurred in the United States, many Americans still have high total cholesterol concentrations. Data from phase I of the National Health and Nutrition Examination Survey III (NHANES III) showed that 49% of the adult US population had cholesterol concentrations ≥5.2 mmol/L (200 mg/dL).5 Whether continued progress in lowering cholesterol concentrations occurred in the United States during the 1990s is not known.
In addition, little is known about the awareness, treatment, and control of hypercholesterolemia. Therefore, our objectives were (1) to describe the mean total cholesterol concentrations in the adult US population by using data from the 1999 to 2000 NHANES and (2) to establish the proportions of adults with hypercholesterolemia who were aware of their condition, who took medications to treat the condition, and who had their cholesterol concentration in the desirable range.
Starting in 1999, NHANES became a continuously operating survey.6 This analysis uses data obtained during 1999 to 2000. A representative sample of the noninstitutionalized civilian US population was selected by using a stratified, multistage sampling design. Trained interviewers, using a computer-assisted personal interview system, interviewed participants at home. Participants were asked to attend the mobile examination center, where they were asked to complete additional questionnaires, undergo various examinations, and provide a blood sample. Persons with low incomes, persons aged ≥60 years, blacks, and Mexican Americans were oversampled. Of 12 160 eligible sample persons, 9965 (81.9%) were interviewed and 9282 (76.3%) were examined. The study received human subjects approval, and participants were asked to sign an informed consent form.
Detailed descriptions about blood collection and processing are provided in the NHANES Laboratory/Medical Technologists Procedures Manual. Specimens were stored at −20°C and were shipped weekly to the Lipoprotein Analytical Laboratory at Johns Hopkins University Hospital. This laboratory participates in the Lipid Standardization Program of the Centers for Disease Control and Prevention and also performed the serum total cholesterol measurements for NHANES III, which was conducted from 1988 to 1994. Serum cholesterol was measured enzymatically on a Hitachi 717 Analyzer (Boehringer Mannheim Diagnostics) using commercial reagents. Serum control pools were obtained from Solomon Park Research Laboratories. A total cholesterol concentration ≥5.2 mmol/L (200 mg/dL) was defined as high. Participants were asked the following question: “Have you ever had your blood cholesterol checked?” Those who answered affirmatively were then asked, “Have you ever been told by a doctor or other health professional that your blood cholesterol level was high?” Those who answered affirmatively were considered aware of having a high cholesterol concentration. Participants who said yes to the questions “To lower your blood cholesterol, have you ever been told by a doctor or other health professional to take prescribed medicine?” and “Are you now following this advice to take prescribed medicine?” were considered on pharmacological treatment. Participants were considered to have controlled cholesterol concentrations if their cholesterol concentration was <5.2 mmol/L (200 mg/dL) or <6.2 mmol/L (240 mg/dL), depending on the cholesterol threshold we used for analysis.
We stratified our analyses by age, sex, and race or ethnicity (white, black, Mexican American, other Hispanic, and other). We limited our analyses to participants aged ≥20 years who attended the mobile examination center. To age-adjust statistics, we directly adjusted to the US population aged ≥20 years in the year 2000. To test the statistical significance of the changes in mean total cholesterol concentration between the 2 surveys, we performed a t test. Standard errors were calculated for means or percentages. The pooled standard error for the difference in means was calculated by taking the square root of the sum of the squared standard errors. We used SUDAAN (Software for the Statistical Analysis of Correlated Data) for analyses to account for the complex sampling design.
Among the 4880 participants aged ≥20 years, the 4148 who had a total cholesterol determination or who were taking cholesterol-lowering medications (4115 had a total cholesterol determination) formed the basis of the analyses.
In NHANES 1999 to 2000, the unadjusted mean total cholesterol concentration was 5.26 mmol/L (203 mg/dL), and the age-adjusted mean total cholesterol concentration was 5.27 mmol/L (203 mg/dL). The mean total cholesterol concentration was similar among men and women (Table 1). Among men, mean total cholesterol concentrations increased with age and peaked among those aged 45 to 54 years. Among women, mean total cholesterol concentrations increased with age and peaked among those aged 55 to 64 years. Among men, Mexican-American participants had the highest and white participants the lowest age-adjusted mean total cholesterol concentrations. Among women, white participants had the highest and Mexican-American women the lowest age-adjusted mean total cholesterol concentrations. Among participants aged 20 to 74 years, the unadjusted and age-adjusted mean total cholesterol concentrations were 5.25 mmol/L (203 mg/dL) and 5.26 (203 mg/dL) for all participants, 5.24 mmol/L (202 mg/dL) and 5.26 (203 mg/dL) for men, and 5.26 mmol/L (204 mg/dL) and 5.26 (203 mg/dL) for women, respectively.
To compare changes in total cholesterol concentrations that had occurred since NHANES III was conducted during 1988 to 1994, we calculated the mean total cholesterol concentrations for that survey. Although the age-adjusted mean total cholesterol concentrations decreased from 5.31 mmol/L (205 mg/dL) to 5.27 mmol/L (203 mg/dL) between the 2 surveys among participants aged ≥20 years, the change was not significant. The age-adjusted mean total cholesterol concentration decreased by 0.02 mmol/L (0.7 mg/dL) among men and by 0.06 mmol/L (2.3 mg/dL) among women, but neither change was significant. Significant decreases were observed among men aged ≥75 years, black men, and Mexican-American women.
Among all participants, 49.6±1.2% had an unadjusted concentration <5.2 mmol/L (200 mg/dL), 32.7±0.9% had an unadjusted concentration 5.2 to <6.2 mmol/L (200 to <240 mg/dL), and 17.8±0.9% had an unadjusted concentration ≥6.2 mmol/L (240 mg/dL). Among men, the respective percentages were 50.3±1.3%, 33.0±1.4%, and 16.7±1.1%. Among women, the respective percentages were 48.9±1.5%, 32.4±1.0%, and 18.7±1.2%. In addition, 55.7±1.2% (unadjusted, 54.9%) of men and 53.5±1.3% (unadjusted, 54.0%) of women had an age-adjusted total cholesterol concentration ≥5.2 mmol/L (200 mg/dL) or reported using cholesterol-lowering medications (Table 2).
Among all participants who had an elevated total cholesterol concentration or who reported using cholesterol-lowering medications, the age-adjusted proportion that was aware of their condition was 35.0% (unadjusted, 40.3%), the age-adjusted proportion being treated was 12.0% (unadjusted, 15.6%), and the age-adjusted proportion with a total cholesterol concentration <5.2 mmol/L (200 mg/dL) was 5.4% (unadjusted, 6.8%; Table 3). Younger participants, women, and Mexican Americans had the lowest rates of cholesterol control. At the cholesterol concentration of ≥6.2 mmol/L (240 mg/dL), the rates of awareness, treatment, and control were higher (Table 4).
An alternative way to present the results in Table 3 is to estimate the percentage of participants who reported using cholesterol-lowering medications among those who were aware of their condition and the percentage of participants who were controlled among those who reported using cholesterol-lowering medications. The unadjusted percentages for all participants were 38.7% and 47.0%, respectively. If the sample is limited to 4115 participants with complete information for total cholesterol concentration, the unadjusted percentage of participants who were aware of their hypercholesterolemia was 39.6%, the percentage of participants who reported using cholesterol-lowering medications among those who were aware was 36.8%, and the percentage of participants who were controlled among those who reported using cholesterol-lowering medications was 47.0%. Thus, out of 100 people with hypercholesterolemia, 39.6% were aware of their condition, 14.5% reported using cholesterol-lowering medications, and 6.8% had a total cholesterol concentration <5.2 mmol/L.
The age-adjusted percentage of participants reporting the current use of cholesterol-lowering medications was 3.1% (men, 2.9%; women, 3.3%) in NHANES III and 7.9% in NHANES 1999 to 2000 (men, 9.0%; women, 6.8%).
Our results highlight 2 important conclusions. First, the trend in population decreases in total cholesterol concentration seems to have markedly slowed. Among US adults aged ≥20 years, total cholesterol concentration decreased by 0.04 mmol/L (1.7 mg/dL; men, 0.02 mmol/L; women, 0.06 mmol/L) between 1988 through 1994 and 1999 through 2000. In comparison, a decrease of 0.21 mmol/L (8 mg/dL) occurred between 1976 through 1980 and 1988 through 1991.4 Second, control of hypercholesterolemia is low. After adjustment for age, ≈5% of adults with hypercholesterolemia (according to a total cholesterol concentration threshold of 5.2 mmol/L or self-reported use of cholesterol-lowering medications) had a total cholesterol concentration <5.2 mmol/L, and 18% of participants with hypercholesterolemia (according to a total cholesterol concentration threshold of 6.2 mmol/L or self-reported use of cholesterol-lowering medications) had a total cholesterol concentration <6.2 mmol/L.
Our findings are consistent with recent results about temporal trends in total cholesterol concentration from the Minnesota Heart Survey, which showed that total cholesterol concentrations did not decline between 1990 through 1992 (mean total cholesterol concentration: men, 203.2 mg/dL; women, 200.6 mg/dL) and 1995 through 1997 (mean total cholesterol concentration: men, 204.8 mg/dL; women, 200.5 mg/dL).7 Several factors may have helped slow the decrease in mean cholesterol concentration. Poor nutrition, inadequate physical activity, inadequate screening, and inadequate treatment may have played roles. In addition, the epidemic of obesity may also have slowed the trend. In the United States, saturated fat intake, an important determinant of serum total cholesterol concentration, as a percentage of total energy intake has been decreasing, but the absolute intake of saturated fat from 1985 through 1995 remained fairly stable.8 A potentially important factor in cholesterol trends is the use of cholesterol-lowering medications, which have increased during the 1990s.9 Our analysis of the NHANES 1999 to 2000 data suggests that control of hypercholesterolemia is low. If participants who used such medications forgot to report their use or were unaware of why they were taking the medications, we may have underestimated the proportion of participants who used cholesterol-lowering medications.
Our understanding about awareness, treatment, and control of hypercholesterolemia remains incomplete. Increases in cholesterol awareness and treatment were shown in the Minnesota Heart Survey from 1980 to 1982 through 1990 to 1992.10 Data from the Behavioral Risk Factor Surveillance System from 1991 through 1999 showed an increase in the proportion of participants who reported having been told that their blood cholesterol was high.11 In NHANES III (1988 to 1994), 51.3% of adults aged ≥21 years who had hypercholesterolemia (defined as a total cholesterol concentration ≥5.2 mmol/L [200 mg/dL] or medication use) were aware of it.12 Using a total cholesterol threshold of ≥6.2 mmol/L (240 mg/dL) raised the proportion of awareness to ≈68%. In a German study, only 65.5% of patients eligible for cholesterol-lowering medications received them.13
Our analysis of the NHANES 1999 to 2000 data suggests that renewed efforts are necessary to lower total cholesterol concentrations in the US population. These efforts should include aggressive promotion of heart-healthy lifestyles to prevent and control hypercholesterolemia and a sustained public health commitment at the national, state, and local levels toward screening, primary and secondary prevention, treatment, and control of hypercholesterolemia.14 When more detailed data are released from NHANES 1999 to 2000, future analyses will be able to examine trends in concentrations of high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, and triglycerides.
American Heart Association. 2002 Heart and Stroke Statistical Update. Dallas, Tex: American Heart Association; 2001.
US Department of Health and Human Services. Reducing Tobacco Use: A Report of the Surgeon General. Atlanta, Ga: US Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Chronic Disease Prevention and Health Promotion, Office of Smoking and Health; 2000.
Burt VL, Cutler JA, Higgins M, et al. Trends in the prevalence, awareness, treatment, and control of hypertension in the adult US population: data from the health examination surveys, 1960 to 1991. Hypertension. 1995; 26: 60–69.
Centers for Disease Control, and Prevention. NHANES 1999–2000 public data release file documentation. Available at: http://www.cdc.gov/nchs/about/major/nhanes/currentnhanes.htm. Accessed February 2003.
Arnett DK, McGovern PG, Jacobs DR Jr, et al. Fifteen-year trends in cardiovascular risk factors (1980–1982 through 1995–1997): the Minnesota Heart Survey. Am J Epidemiol. 2002; 156: 929–935.