Prevalence of Abnormal Lipid Levels Among Youths --- United States, 1999--2006

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Cardiovascular disease (CVD) is the leading cause of death among adults in the United States (1). CVD risk factors, including abnormal lipid levels and elevated body mass index (BMI), often emerge during childhood and adolescence (2). In 2008, the American Academy of Pediatrics (AAP) established recommendations for targeted screening of youths aged ≥2 years for abnormal blood lipid levels (2). To provide prevalence data on abnormal lipid levels among youths, eligibility for lipid screening based on BMI, and eligibility for therapeutic lifestyle counseling among overweight youths, CDC analyzed results from the National Health and Nutrition Examination Survey (NHANES) for 1999--2006. This report describes the results of that analysis, which found that the prevalence of abnormal lipid levels among youths aged 12--19 years was 20.3%. This prevalence varied by BMI; 14.2% of normal weight youths, 22.3% of overweight and 42.9% of obese had at least one abnormal lipid level. Among all youths, 32% had a high BMI and therefore would be candidates for lipid screening under AAP recommendations. Given the high prevalence of abnormal lipid levels among youths who are overweight and obese in this study, clinicians should be aware of lipid screening guidelines, especially recommendations for screening youths who are overweight or obese.

NHANES is a continuous cross-sectional survey of the health and nutritional status of the U.S. civilian, noninstitutionalized population. Each year, approximately 6,000 persons are selected to participate in the survey through a complex, multistage probability design.* All NHANES surveys include a household interview and a detailed physical examination that includes anthropometric measurements. A randomly selected sample of NHANES participants is asked to fast for 8--24 hours. Only participants who have fasted at least 8 hours before blood specimens are taken for laboratory testing are included in the fasting sample. The results from the fasting subsample are weighted to account for the probability of selection and nonresponse.

NHANES data are released in 2-year increments; this analysis was conducted with data from the last four survey cycles: 1999--2000, 2001--2002, 2003--2004, and 2005--2006. During 1999--2006, approximately 78% of selected persons completed a physical examination component in NHANES mobile examination centers. The initial combined sample from the four surveys included 9,187 youths, aged 12--19 years, who took part in home interviews and were examined at mobile examination centers. The sample of youths who provided fasting blood samples for lipid profile testing was 3,733. From those, 73 youths who reported being pregnant or had a positive urine pregnancy test, and 535 youths for whom data were missing were excluded, for a final study sample of 3,125 youths (Table 1).

Age in years and race/ethnicity were self-reported at the time of participation. Youths were classified as non-Hispanic white, non-Hispanic black, or Hispanic. Asian youths and persons classified of other races are included in the overall analyses, but estimates for these specific groups are not reported because of small sample sizes and unstable estimates. Serum levels for youths were classified for low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), and triglycerides according to National Cholesterol Education Program and American Heart Association cutoff points used in the AAP screening guidelines (2) (Table 2). AAP guidelines for targeted lipid screening of youths are based on family history of high blood cholesterol, family history of premature CVD (men aged ≤55 years or women aged ≤65 years), unknown family history of high blood cholesterol or premature CVD, or the presence of at least one major CVD risk factor (smoking, hypertension, diabetes, or overweight/obesity) (2). The percentage of youths who were candidates for lipid screening in this study was determined based on BMI percentiles† (normal weight, overweight, obese). Eligibility for therapeutic lifestyle counseling among overweight and obese youths was determined based on AAP guidelines for screening and treatment (2).§ Significant differences in the prevalence of abnormal lipids as a function of demographic factors and overweight or obesity status were assessed using chi-square tests. Prevalence ratios (PRs) were used to estimate relative risk for abnormal lipids levels.

Among all youths, 20.3% had at least one abnormal lipid level based on cutoff points for high LDL-C (≥130 mg/dL), low HDL-C (≤35 mg/dL), and high triglyceride levels (≥150 mg/dL) (2) (Table 2). Compared with youths who were normal weight, overweight and obese youths were significantly more likely to have at least one abnormal lipid level (PR = 1.6 and PR = 3.0, respectively). A greater proportion of boys had low HDL-C compared with girls (11.0% versus 4.0%), and youths aged 18--19 years were more likely to have low HDL-C (10.4%) or high triglycerides (16.4%) compared with youths aged 12--13 years (4.7% and 9.5%, respectively). Youths aged 14--15 years also were more likely to have low HDL-C (8.7%) compared with youths aged 12--13 years (4.7%). High LDL-C levels differed little across age groups among the youths. The percentage of non-Hispanic white youths with low HDL-C (8.5%) or high triglycerides (12.1%) was higher compared with levels for non-Hispanic black youths (4.7% and 3.7%, respectively).

Based solely on their BMI (15% overweight youths and 17% obese youths), 32% of all youths would be candidates for lipid screening. The percentages of overweight or obese youths who were candidates for therapeutic lifestyle counseling based on lipid levels were 22.3% and 42.9%, respectively.

Reported by

AL May, PhD, EV Kuklina, MD, PhD, PW Yoon, ScD, Div for Heart Disease and Stroke Prevention, National Center for Chronic Disease Prevention and Health Promotion, CDC.

Editorial Note

Recommendations for screening youths for lipid disorders differ among various recommending bodies. In 2007, the U.S. Preventive Services Task Force (USPSTF)¶ concluded that the evidence was insufficient to recommend for or against routine screening for lipid disorders in infants, children, adolescents, or young adults (up to age 20 years). USPSTF has not revised this recommendation. AAP takes a more aggressive stance on screening policy, recommending targeted screening of youths based on family history and other CVD-related risk factors. The results of the analysis in this report indicate that under the AAP recommendations, 32% of all youths were in a population recommended for lipid screening based solely on their weight status. The results also indicate that, during 1999--2006, an estimated one fifth of all youths had at least one lipid abnormality, and among obese youths, the prevalence was 43%. Although previous studies have demonstrated the association between higher BMI and abnormal lipid profiles in youths (3), this analysis reports the prevalence of abnormal lipid profiles among youths by BMI status in the United States using nationally representative data.

In this analysis, differences in lipid levels also were associated with sex, age, and race/ethnicity. These findings are similar to previous studies, which showed that girls tend to have higher HDL-C levels compared with boys after puberty (3), older youths are more likely to have abnormal lipid levels compared with younger youths (4), and fewer non-Hispanic black youths have low HDL-C and high triglyceride levels compared with non-Hispanic white youths (3).

Untreated abnormal lipid levels in childhood and adolescence are linked to increased risk for CVD in adulthood (2). Targeted screening of youths for abnormal lipid levels can identify those youths who might benefit from interventions that reduce the risk for CVD. Recommended interventions focus on dietary changes (e.g., reduced consumption of saturated fat and dietary cholesterol, and increased consumption of dietary fiber) to improve LDL-C (5,6). Weight management through an improved diet and nutritional counseling also is recommended as a primary treatment of abnormal lipid levels. Finally, studies suggest that physical activity might improve HDL-C and triglyceride levels, and to some extent, LDL-C concentrations (7). Although therapeutic lifestyle counseling is the first course of action in reducing abnormal lipid levels among youths, AAP recommends considering pharmacologic interventions to treat children whose LDL remains persistently high even after therapeutic lifestyle counseling (2). However, this study and a previous study of children aged 12--17 years using the same NHANES dataset determined that less than 1% of adolescents had lipid levels high enough to warrant drug therapy according to AAP guidelines (8).

The findings in this report are subject to at least one limitation. Although the analysis could determine the proportion of all youths who were candidates for lipid screening based solely on BMI, it could not determine the proportion of all youths who were candidates for lipid screening based on other CVD factors cited by AAP, because NHANES data do not include family history information.

Based on the findings in this study, clinicians should be aware of lipid screening guidelines and recommended interventions for children and youths who are overweight or obese. Recently, USPSTF also recommended routine screening for overweight and obesity among youths (9). Health-care providers can refer eligible youths to nutritional counseling, community fitness programs, and school-based lifestyle programs. Surveillance data regarding youth obesity levels, lipid screening practices, and trends in CVD risk factors can aid public health practitioners in implementing population-based lifestyle programs and anticipating future screening needs and eligibility criteria.

References

1. Lloyd-Jones D, Adams R, Carnethon M, et al. Heart disease and stroke statistics---2009 update: a report from the American Heart Association Statistics Committee and Stroke Statistics Subcommittee. Circulation 2009;119:e21--181.
2. Daniels SR, Greer FR. Lipid screening and cardiovascular health in childhood. Pediatrics 2008;122:198--208.
3. Dai S, Fulton JE, Harrist RB, Grunbaum JA, Steffen LM, Labarthe DR. Blood lipids in children: age-related patterns and association with body-fat indices: Project HeartBeat! Am J Prev Med 2009;37(1 Suppl):S56--64.
4. Berenson GS, Srinivasan SR, Cresanta JL, Foster TA, Webber LS. Dynamic changes of serum lipoproteins in children during adolescence and sexual maturation. Am J Epidemiol 1981;113:157--70.
5. Gidding SS, Dennison BA, Birch LL, et al. Dietary recommendations for children and adolescents: a guide for practitioners: consensus statement from the American Heart Association. Circulation 2005;112:2061--75.
6. McCrindle BW, Urbina EM, Dennison BA, et al. Drug therapy of high-risk lipid abnormalities in children and adolescents: a scientific statement from the American Heart Association Atherosclerosis, Hypertension, and Obesity in Youths Committee, Council of Cardiovascular Disease in the Young, with the Council on Cardiovascular Nursing. Circulation 2007;115:1948--67.
7. Maron BJ, Chaitman BR, Ackerman MJ, et al. Recommendations for physical activity and recreational sports participation for young patients with genetic cardiovascular diseases. Circulation 2004;109:2807--16.
8. Ford ES, Li C, Zhao G, Mokdad AH. Concentrations of low-density lipoprotein cholesterol and total cholesterol among children and adolescents in the United States. Circulation 2009;119:1108--15.
9. US Preventive Services Task Force. Screening for obesity in children and adolescents: U.S. Preventive Services Task Force recommendation statement. Pediatrics 2010;126:361--7.

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