Effect of Obesity and High Blood Pressure on Plasma Lipid Levels in Children and Adolescents
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《小儿科》
Department of Medicine, Thomas Jefferson University, Philadelphia, Pennsylvania
A.I. duPont Hospital for Children, Wilmington, Delaware
ABSTRACT
Objective. To examine the extent of blood lipid abnormalities in overweight children and to determine whether the prevalence of dyslipidemia is different in overweight children with elevated blood pressure (BP) compared with overweight children with normal BP (NBP).
Methods. A retrospective, case-control study on 497 patients 2 to 18 years of age at the Nemours Weight Management Clinic of duPont Hospital for Children was conducted to compare the prevalence of abnormal plasma lipid levels in overweight children with high BP with overweight children with NBP.
Results. Elevated BP was detected in 34.7% of the sample; 27.9% had prehypertension (pre-HTN), and 6.8% had HTN. The rates of abnormal plasma lipid levels were high among overweight children with both NBP and HTN. Significantly more boys with high BP had low high-density lipoprotein cholesterol compared with boys with NBP (49.4% vs 27.6%). Significantly more severely obese boys had low high-density lipoprotein cholesterol compared with moderately obese boys (40.3% vs 29.3%). The prevalence of elevated BP was much greater in severely obese boys and girls (46.5% and 39%) than moderately obese boys and girls (28.1% and 23.1%).
Conclusions. The high prevalence of dyslipidemia found in this overweight sample supports recent recommendations to collect plasma lipid levels in not only overweight children with BP 90th percentile but also in all overweight children.
Key Words: obesity blood pressure lipids hypertension children adolescents
Abbreviations: BP, blood pressure NBP, normal blood pressure pre-HTN, prehypertension HTN, hypertension HDL, high-density lipoprotein LDL, low-density lipoprotein SBP, systolic blood pressure DBP, diastolic blood pressure TG, triglyceride
It is estimated that 15% of children and adolescents in the United States are overweight, defined as a BMI 95th percentile, and these numbers are climbing.1 Overweight individuals are much more likely to have dyslipidemia and elevated blood pressure (BP), 2 clinical measures that dramatically increase risk for cardiovascular and metabolic diseases.2 The metabolic syndrome, a collection of clinical measures that include insulin resistance, abnormal glucose tolerance, abnormal lipid levels, and high BP, is linked with obesity.3 Cook et al4 found that 30% of overweight children in the United States meet the criteria for the metabolic syndrome.
The high prevalence of these risk factors among youths has increased the importance of screening for metabolic markers in clinical practice. The American Heart Association has advocated for lipid assessment in all overweight children.5 The Fourth Report on the Diagnosis, Evaluation and Treatment of High Blood Pressure in Children and Adolescents recommends obtaining a fasting lipid panel for all overweight children with BP at the 90th percentile or greater to evaluate for comorbidities.6 However, these recommendations are not included in recent cholesterol screening guidelines.7,8 The prevalence of dyslipidemia in overweight children, as defined by the new BMI tables (www.cdc.gov/growthcharts),9 and its association with high BP is unknown. The purpose of this study was to examine the extent of blood lipid abnormalities in obese children and to determine whether the prevalence of dyslipidemia is different in overweight children with elevated BP compared with overweight children with normal BP.
METHODS
A retrospective, case-control study was conducted on clinical records of patients who were enrolled at the Nemours Children's Weight Management Clinic at A.I. duPont Hospital for Children between 1996 and 2004. This study, which involved a chart review of de-identified clinical data, was approved by the Institutional Review Board at A.I. duPont Hospital for Children. Records were examined on patients who were between 2 and 18 years of age and had a BMI of 95th percentile for age and gender. Patients with Down syndrome or obesity-related syndromes, including Prader Willi and hypothyroidism, were excluded.
Data obtained on each case in the Weight Management Clinic included age, weight, height, and BMI at the visit when laboratory measures were obtained. The method for BP measurement in the Weight Management Clinic was auscultation from the right arm with the patient seated, using a mercury sphygmomanometer and appropriately sized cuff.10 The value for BP that was used for each patient was the calculated average of up to 5 BP measurements recorded at separate visits. The average systolic BP (SBP), average diastolic BP (DBP), and height percentiles were determined for each case. The BMI z score was also derived for each case. Blood lipids were measured at clinical laboratories on a fasting sample and included total cholesterol, high-density lipoprotein (HDL) cholesterol, and triglyceride (TG) levels. From the lipid data, low-density lipoprotein (LDL) cholesterol was calculated using the Friedewald equation.11 Data from the clinical laboratory measurement of fasting plasma glucose and fasting plasma insulin were also obtained for each case.
The BP group assessment was based on the average of multiple BP measurements. Patients with average systolic and DBP <90th percentile were classified as having normal BP (NBP). Patients with average systolic or DBP >90th but <95th percentile were classified as having prehypertension (pre-HTN). Adolescents with average BP >120/80 mm Hg (but <95th percentile) were also classified as having pre-HTN. Patients with average systolic or DBP 95th percentile were designated as having hypertension (HTN).6 Overweight patients with a BMI z score <2.5 were classified as moderately obese, and patients with a BMI z score of >2.5 were classified as severely obese.12 Plasma lipid levels that were designated abnormal were total cholesterol 200 mg/dL, TGs 150 mg/dL, LDL cholesterol 130 mg/dL, and HDL cholesterol <40 mg/dL.13
The sample was stratified by BP percentile and BMI z score and analyzed by gender. Because BP and BMI z score are age corrected and lipid values are generally constant among the age groups in this cohort, the sample was not stratified by age. The mean and SD of the BMI, cholesterol, LDL cholesterol, HDL cholesterol, and TGs were calculated, and analysis of variance single-factor tests were used for analysis. The prevalence of abnormal levels of each plasma lipid were calculated and compared among BP groups and between moderately and severely obese groups using 2 analysis. Relationships between continuous variables were examined by Pearson correlation analyses to derive simple correlation coefficients.
RESULTS
The mean values for age, BMI, and lipid measures according to BP group are provided for boys in Table 1 and for girls in Table 2. Plasma lipid data were available on 497 overweight children and adolescents. In this sample of overweight children, 27.9% (n = 139) had pre-HTN and 6.8% (n = 34) had HTN. High BP classification was driven more by systolic than DBP. There is no significant difference in mean age among BP groups in girls, but among boys, the pre-HTN group is older. Although BMI is higher in the pre-HTN and HTN groups, among boys, there is no significant difference in BMI z score. Among girls, BMI z score is higher in the pre-HTN and HTN groups. Both pre-HTN and HTN boys have significantly lower HDL cholesterol and higher TG levels compared with NBP boys. However, among overweight girls, there were no significant differences of plasma lipids among the BP groups.
The prevalence of abnormal lipid levels among the groups with NBP and elevated BP (pre-HTN combined with HTN) for boys and girls is provided in Table 3. Boys with elevated BP have a higher prevalence of low HDL cholesterol and high TG levels (but this latter difference is borderline significant). Among girls, there is no significant difference in the prevalence of abnormal lipid values among BP groups.
The prevalence of abnormal lipid levels according to severity of obesity is provided in Table 4. Severely obese (BMI z score >2.5) boys have a lower prevalence of elevated total cholesterol and LDL cholesterol, a difference that is statistically significant. There is no difference in the prevalence of elevated TGs between moderately and severely obese boys. Severely obese boys have a higher prevalence of low HDL cholesterol compared with moderately obese boys. Among girls, the severely obese group has a lower prevalence of elevated TGs.
Within this overweight sample of children and adolescents, the relationships of the recorded plasma insulin concentration with BP and plasma lipid concentrations were also examined. Using Pearson correlation analyses, there were statistically significant simple correlation coefficients, in both boys and girls, of plasma insulin concentration with SBP (r = 0.32; P < .001), DBP (r = 0.20; P < .01), and TGs (r = 0.22; P < .001). In boys, there was also a significant correlation of insulin with HDL cholesterol (r = -.23; P < .001). There were no statistically significant correlations of the fasting plasma glucose with BP or plasma lipid concentration. Among the NPB group, there were 19 (5.9%) patients with a fasting plasma glucose >100 mg/dL, indicative of impaired fasting glucose. Among the combined high BP groups, there were 15 (8.6%) patients with fasting glucose >100 mg/dL. The percentage of patients with impaired fasting glucose was not different between the BP groups. There were no cases with fasting glucose concentration 126 mg/dL.
The relationship between obesity severity and high BP in this cohort is depicted in Fig 1. Among moderately obese boys, 23.2% (n = 82) have pre-HTN and 4.9% have HTN. Among moderately obese girls, 19.6% (n = 143) have pre-HTN and 3.5% have HTN. In contrast, among severely obese boys, 39.6% (n = 144) have pre-HTN and 6.9% have HTN. Among severely obese girls, 27.3% (n = 128) have pre-HTN and 11.7% have HTN. Rates of pre-HTN and HTN increase as obesity severity increases.
DISCUSSION
The findings in this study reveal a high prevalence of dyslipidemia in overweight children and adolescents, regardless of BP percentile or BMI z score. Approximately 25% of NBP overweight children of both genders have high cholesterol, which is higher than the overall youth population of the Bogalusa Heart Study.14 Among overweight boys with elevated BP, nearly 50% have low HDL cholesterol levels. To reduce error, as a result of variability in BP level, the ascertainment of BP for each case was based on the average of multiple BP measurements that were obtained on separate clinic visits. With this method, the prevalence of elevated BP was found to be greater than that in the general pediatric population,6 and the prevalence of elevated BP increased with severity of obesity.
The presence of high BP and abnormal lipid levels in overweight children meets the criteria of the metabolic syndrome, also known as the insulin resistance syndrome.3 In an analysis of the National Health and Nutritional Examination Survey data, Cook et al4 estimated that nearly 30% of overweight adolescents in the United States meet the criteria for the metabolic syndrome. The results of our analysis of lipid and BP data on this sample of overweight children are consistent with their estimates of the prevalence of the metabolic syndrome. Our data also demonstrate a significant correlation of fasting plasma insulin correlation with BP level and plasma lipid concentrations. The metabolic syndrome is associated with an increased risk for development of cardiovascular and metabolic diseases, such as type 2 diabetes and atherosclerosis.5,15 The combination of obesity, high BP, and dyslipidemia has an additive effect of increasing the severity of atherosclerotic lesions in young people.16 Elevated LDL cholesterol and BMI levels are also predictive of carotid intima-media thickness in adolescents, which is strongly associated with coronary atherosclerosis and cardiovascular risk.17
Previous reports describe greater expression of cardiovascular risk factors with increasing severity of childhood obesity. Weiss et al12 reported that the prevalence of the metabolic syndrome increased from 38.7% in the moderately obese group to 49.7% in the severely obese group (BMI z score >2.5). In a study of glucose tolerance in overweight children, Sinha et al18 reported that impaired glucose tolerance was detected in 25% of severely obese children and adolescents. Our data on lipid abnormalities detected only a modest increase in the prevalence of abnormal HDL in the severely obese group. However, elevated BP was found in 46.5% of severely obese boys and 39% of severely obese girls compared with 28.1% of boys and 23.1% of girls in the moderately obese groups. Therefore, our data are consistent with other reports that describe an increase in cardiovascular risk factors as severity of obesity increases.
A limitation of this study is the possibility of selection bias because the study sample was based on patients who were referred to a weight management clinic. The range for the BMI z score indicates that our sample includes cases of extreme obesity, which may not be typical of most overweight cases in a clinician's office. Children with increased risk may be more likely to be referred to a weight management program. Elevated BP was found in 34.7% of this overweight clinic sample. This prevalence of elevated BP, however, is consistent with the rate of elevated BP detected in school-based screening of generally healthy high school students reported by Sorof et al,19 in which 34% of adolescents with BMI 95th percentile had high BP. In our study, the plasma lipids were analyzed at different clinical laboratories, which may increase variability. However, the high rates of dyslipidemia found in our sample are comparable to rates of dyslipidemia described in the National Health and Nutritional Examination Survey population data for overweight and are also comparable to the clinical sample of overweight children reported by Weiss et al.12
Another limitation in our study was the inability to analyze the contribution of race to the plasma lipid and BP measurements. TG levels in black men and women are lower than those in white men and women. In both men and women, the mean plasma TG level is reported to be 20 mg/dL lower in black individuals compared with their white counterparts.20 HDL cholesterol levels are higher in black compared with white individuals, a difference that cannot be explained by racial differences in BMI or other factors that have an effect on plasma HDL cholesterol concentration, such as alcohol intake or smoking.21,22 The race of the patients was not consistently recorded in clinical records, thus limiting our ability to examine race effect. Therefore, it is likely that unanalyzed race effects may have contributed to some unevenness in the results on BP and lipid relationships.
The data from this clinical sample of overweight children support the recent recommendation to obtain plasma lipid measures on overweight children with BP 90th percentile.6 Because of the high prevalence of dyslipidemia found in NBP children in this overweight sample, it would be beneficial to obtain plasma lipid measurements on all overweight children, regardless of BP status, as recommended by the American Heart Association.5 Detection of children with multiple risk factors would identify those who require more intense interventions to reduce their cardiovascular risk.
ACKNOWLEDGMENTS
This work was supported in part by National Institutes of Health grants HL51547, DK46107, and HI007845-06.
FOOTNOTES
Accepted Nov 18, 2004.
No conflict of interest declared.
REFERENCES
Ogden CL, Flegel KM, Carroll MD, Johnson CL. Prevalence and trends in overweight among US children and adolescents, 1999–2000. JAMA. 2002;288 :1728 –1732
Gidding S. Relationships between blood pressure and lipids in childhood. Child Hypertens. 1993;40 :41 –49
Reaven G. Role of insulin resistance in human disease. Diabetes. 1988;37 :1595 –1607
Cook S, Weitzman M, Auinger P, Nguyen M, Dietz W. Prevalence of a metabolic syndrome phenotype in adolescents. Arch Pediatr Adolesc Med. 2003;157 :821 –827
Gidding S, Leibel RL, Daniels S, Rosenbaum M, Van Horn L, Marx G. Understanding obesity in youth: a statement for healthcare professionals from the Committee on Atherosclerosis and Hypertension in the Young of the Council on Cardiovascular Disease in Young and the Nutrition Committee, American Heart Association. Circulation. 1996;94 :3383 –3387
National High Blood Pressure Education Program Working Group on High Blood Pressure in Children and Adolescents. The fourth report on the diagnosis, evaluation, and treatment of high blood pressure in children and adolescents. Pediatrics. 2004;114 :555 –576
American Academy of Pediatrics. Committee on Nutrition. Cholesterol in childhood. Pediatrics. 1998;101 :141 –147
National Cholesterol Education Program (NCEP). Highlights of the report of the Expert Panel on Blood Cholesterol Levels in Children and Adolescents. Pediatrics. 1992;89 :495 –501
National High Blood Pressure Education Program Working Group on Hypertension Control in Children and Adolescents. Update on the 1987 Task Force Report on High Blood Pressure in Children and Adolescents: a working group report from the National High Blood Pressure Education Program. Pediatrics. 1996;98 :649 –658
Friedewald WT, Levy RI, Fredrickson DS. Estimation of the concentra-tion of low-density lipoprotein cholesterol in plasma, without use of the preparative ultracentrifuge. Clin Chem. 1972;18 :499 –502
Weiss R, Dziura J, Burgert T, et al. Obesity and the metabolic syndrome in children and adolescents. N Engl J Med. 2004;350 :2362 –2374
Third Report of the National Cholesterol Education Program Expert Panel on Detection, Evaluation and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III). Bethesda, MD: National Heart, Lung, and Blood Institute; 2001
Freedman DS, Dietz WH, Srinivasan SR, Berenson GS. The relation of overweight to cardiovascular risk factors among children and adolescents: the Bogalusa Heart Study. Pediatrics. 1999;103 :1175 –1182
Steinberger J, Daniels SR; American Heart Association Atherosclerosis, Hypertension, and Obesity in the Young Committee (Council on Cardiovascular Disease in the Young); American Heart Association Diabetes Committee (Council on Nutrition, Physical Activity, and Metabolism). Obesity, insulin resistance, diabetes, and cardiovascular risk in children: an American Heart Association scientific statement from the Atherosclerosis, Hypertension, and Obesity in the Young Committee (Council on Cardiovascular Disease in the Young) and the Diabetes Committee (Council on Nutrition, Physical Activity, and Metabolism). Circulation. 2003;107 :1448 –1453
Berenson G, Srinivasan S, Bao W, Newman W, Tracy R, Wattigney W. Association between multiple cardiovascular risk factors and atherosclerosis in children and young adults. N Engl J Med. 1998;338 :1650 –1656
Li S, Chen W, Srinivasan S, et al. Childhood cardiovascular risk factors and carotid vascular changes in adulthood: the Bogalusa Heart Study. JAMA. 2003;290 :2271 –2276
Sinha R, Fisch G, Teague B, et al. Prevalence of impaired glucose tolerance among children and adolescents with marked obesity. N Engl J Med. 2002;346 :802 –810
Sorof JM, Daniels S. Obesity and hypertension in children. Hypertension. 2002;40 :441 –455
Hutchinson RG, Watson RI, Davis CE, et al. Racial differences in risk factors for atherosclerosis. The ARIC study: Atherosclerosis Risk in Communities. Angiology. 1997;48 :279 –290
Hall WD, Clark LT, Wenger NK, et al. The metabolic syndrome in African Americans: a review. Ethn Dis. 2003;13 :414 –428
Sprafka JM, Norsted SW, Folsom AR, et al. Life-style factors do not explain racial differences in high-density lipoprotein cholesterol: the Minnesota Heart Survey. Epidemiology. 1992;3 :156 –163(Gillian S. Boyd, BS, Joan)
A.I. duPont Hospital for Children, Wilmington, Delaware
ABSTRACT
Objective. To examine the extent of blood lipid abnormalities in overweight children and to determine whether the prevalence of dyslipidemia is different in overweight children with elevated blood pressure (BP) compared with overweight children with normal BP (NBP).
Methods. A retrospective, case-control study on 497 patients 2 to 18 years of age at the Nemours Weight Management Clinic of duPont Hospital for Children was conducted to compare the prevalence of abnormal plasma lipid levels in overweight children with high BP with overweight children with NBP.
Results. Elevated BP was detected in 34.7% of the sample; 27.9% had prehypertension (pre-HTN), and 6.8% had HTN. The rates of abnormal plasma lipid levels were high among overweight children with both NBP and HTN. Significantly more boys with high BP had low high-density lipoprotein cholesterol compared with boys with NBP (49.4% vs 27.6%). Significantly more severely obese boys had low high-density lipoprotein cholesterol compared with moderately obese boys (40.3% vs 29.3%). The prevalence of elevated BP was much greater in severely obese boys and girls (46.5% and 39%) than moderately obese boys and girls (28.1% and 23.1%).
Conclusions. The high prevalence of dyslipidemia found in this overweight sample supports recent recommendations to collect plasma lipid levels in not only overweight children with BP 90th percentile but also in all overweight children.
Key Words: obesity blood pressure lipids hypertension children adolescents
Abbreviations: BP, blood pressure NBP, normal blood pressure pre-HTN, prehypertension HTN, hypertension HDL, high-density lipoprotein LDL, low-density lipoprotein SBP, systolic blood pressure DBP, diastolic blood pressure TG, triglyceride
It is estimated that 15% of children and adolescents in the United States are overweight, defined as a BMI 95th percentile, and these numbers are climbing.1 Overweight individuals are much more likely to have dyslipidemia and elevated blood pressure (BP), 2 clinical measures that dramatically increase risk for cardiovascular and metabolic diseases.2 The metabolic syndrome, a collection of clinical measures that include insulin resistance, abnormal glucose tolerance, abnormal lipid levels, and high BP, is linked with obesity.3 Cook et al4 found that 30% of overweight children in the United States meet the criteria for the metabolic syndrome.
The high prevalence of these risk factors among youths has increased the importance of screening for metabolic markers in clinical practice. The American Heart Association has advocated for lipid assessment in all overweight children.5 The Fourth Report on the Diagnosis, Evaluation and Treatment of High Blood Pressure in Children and Adolescents recommends obtaining a fasting lipid panel for all overweight children with BP at the 90th percentile or greater to evaluate for comorbidities.6 However, these recommendations are not included in recent cholesterol screening guidelines.7,8 The prevalence of dyslipidemia in overweight children, as defined by the new BMI tables (www.cdc.gov/growthcharts),9 and its association with high BP is unknown. The purpose of this study was to examine the extent of blood lipid abnormalities in obese children and to determine whether the prevalence of dyslipidemia is different in overweight children with elevated BP compared with overweight children with normal BP.
METHODS
A retrospective, case-control study was conducted on clinical records of patients who were enrolled at the Nemours Children's Weight Management Clinic at A.I. duPont Hospital for Children between 1996 and 2004. This study, which involved a chart review of de-identified clinical data, was approved by the Institutional Review Board at A.I. duPont Hospital for Children. Records were examined on patients who were between 2 and 18 years of age and had a BMI of 95th percentile for age and gender. Patients with Down syndrome or obesity-related syndromes, including Prader Willi and hypothyroidism, were excluded.
Data obtained on each case in the Weight Management Clinic included age, weight, height, and BMI at the visit when laboratory measures were obtained. The method for BP measurement in the Weight Management Clinic was auscultation from the right arm with the patient seated, using a mercury sphygmomanometer and appropriately sized cuff.10 The value for BP that was used for each patient was the calculated average of up to 5 BP measurements recorded at separate visits. The average systolic BP (SBP), average diastolic BP (DBP), and height percentiles were determined for each case. The BMI z score was also derived for each case. Blood lipids were measured at clinical laboratories on a fasting sample and included total cholesterol, high-density lipoprotein (HDL) cholesterol, and triglyceride (TG) levels. From the lipid data, low-density lipoprotein (LDL) cholesterol was calculated using the Friedewald equation.11 Data from the clinical laboratory measurement of fasting plasma glucose and fasting plasma insulin were also obtained for each case.
The BP group assessment was based on the average of multiple BP measurements. Patients with average systolic and DBP <90th percentile were classified as having normal BP (NBP). Patients with average systolic or DBP >90th but <95th percentile were classified as having prehypertension (pre-HTN). Adolescents with average BP >120/80 mm Hg (but <95th percentile) were also classified as having pre-HTN. Patients with average systolic or DBP 95th percentile were designated as having hypertension (HTN).6 Overweight patients with a BMI z score <2.5 were classified as moderately obese, and patients with a BMI z score of >2.5 were classified as severely obese.12 Plasma lipid levels that were designated abnormal were total cholesterol 200 mg/dL, TGs 150 mg/dL, LDL cholesterol 130 mg/dL, and HDL cholesterol <40 mg/dL.13
The sample was stratified by BP percentile and BMI z score and analyzed by gender. Because BP and BMI z score are age corrected and lipid values are generally constant among the age groups in this cohort, the sample was not stratified by age. The mean and SD of the BMI, cholesterol, LDL cholesterol, HDL cholesterol, and TGs were calculated, and analysis of variance single-factor tests were used for analysis. The prevalence of abnormal levels of each plasma lipid were calculated and compared among BP groups and between moderately and severely obese groups using 2 analysis. Relationships between continuous variables were examined by Pearson correlation analyses to derive simple correlation coefficients.
RESULTS
The mean values for age, BMI, and lipid measures according to BP group are provided for boys in Table 1 and for girls in Table 2. Plasma lipid data were available on 497 overweight children and adolescents. In this sample of overweight children, 27.9% (n = 139) had pre-HTN and 6.8% (n = 34) had HTN. High BP classification was driven more by systolic than DBP. There is no significant difference in mean age among BP groups in girls, but among boys, the pre-HTN group is older. Although BMI is higher in the pre-HTN and HTN groups, among boys, there is no significant difference in BMI z score. Among girls, BMI z score is higher in the pre-HTN and HTN groups. Both pre-HTN and HTN boys have significantly lower HDL cholesterol and higher TG levels compared with NBP boys. However, among overweight girls, there were no significant differences of plasma lipids among the BP groups.
The prevalence of abnormal lipid levels among the groups with NBP and elevated BP (pre-HTN combined with HTN) for boys and girls is provided in Table 3. Boys with elevated BP have a higher prevalence of low HDL cholesterol and high TG levels (but this latter difference is borderline significant). Among girls, there is no significant difference in the prevalence of abnormal lipid values among BP groups.
The prevalence of abnormal lipid levels according to severity of obesity is provided in Table 4. Severely obese (BMI z score >2.5) boys have a lower prevalence of elevated total cholesterol and LDL cholesterol, a difference that is statistically significant. There is no difference in the prevalence of elevated TGs between moderately and severely obese boys. Severely obese boys have a higher prevalence of low HDL cholesterol compared with moderately obese boys. Among girls, the severely obese group has a lower prevalence of elevated TGs.
Within this overweight sample of children and adolescents, the relationships of the recorded plasma insulin concentration with BP and plasma lipid concentrations were also examined. Using Pearson correlation analyses, there were statistically significant simple correlation coefficients, in both boys and girls, of plasma insulin concentration with SBP (r = 0.32; P < .001), DBP (r = 0.20; P < .01), and TGs (r = 0.22; P < .001). In boys, there was also a significant correlation of insulin with HDL cholesterol (r = -.23; P < .001). There were no statistically significant correlations of the fasting plasma glucose with BP or plasma lipid concentration. Among the NPB group, there were 19 (5.9%) patients with a fasting plasma glucose >100 mg/dL, indicative of impaired fasting glucose. Among the combined high BP groups, there were 15 (8.6%) patients with fasting glucose >100 mg/dL. The percentage of patients with impaired fasting glucose was not different between the BP groups. There were no cases with fasting glucose concentration 126 mg/dL.
The relationship between obesity severity and high BP in this cohort is depicted in Fig 1. Among moderately obese boys, 23.2% (n = 82) have pre-HTN and 4.9% have HTN. Among moderately obese girls, 19.6% (n = 143) have pre-HTN and 3.5% have HTN. In contrast, among severely obese boys, 39.6% (n = 144) have pre-HTN and 6.9% have HTN. Among severely obese girls, 27.3% (n = 128) have pre-HTN and 11.7% have HTN. Rates of pre-HTN and HTN increase as obesity severity increases.
DISCUSSION
The findings in this study reveal a high prevalence of dyslipidemia in overweight children and adolescents, regardless of BP percentile or BMI z score. Approximately 25% of NBP overweight children of both genders have high cholesterol, which is higher than the overall youth population of the Bogalusa Heart Study.14 Among overweight boys with elevated BP, nearly 50% have low HDL cholesterol levels. To reduce error, as a result of variability in BP level, the ascertainment of BP for each case was based on the average of multiple BP measurements that were obtained on separate clinic visits. With this method, the prevalence of elevated BP was found to be greater than that in the general pediatric population,6 and the prevalence of elevated BP increased with severity of obesity.
The presence of high BP and abnormal lipid levels in overweight children meets the criteria of the metabolic syndrome, also known as the insulin resistance syndrome.3 In an analysis of the National Health and Nutritional Examination Survey data, Cook et al4 estimated that nearly 30% of overweight adolescents in the United States meet the criteria for the metabolic syndrome. The results of our analysis of lipid and BP data on this sample of overweight children are consistent with their estimates of the prevalence of the metabolic syndrome. Our data also demonstrate a significant correlation of fasting plasma insulin correlation with BP level and plasma lipid concentrations. The metabolic syndrome is associated with an increased risk for development of cardiovascular and metabolic diseases, such as type 2 diabetes and atherosclerosis.5,15 The combination of obesity, high BP, and dyslipidemia has an additive effect of increasing the severity of atherosclerotic lesions in young people.16 Elevated LDL cholesterol and BMI levels are also predictive of carotid intima-media thickness in adolescents, which is strongly associated with coronary atherosclerosis and cardiovascular risk.17
Previous reports describe greater expression of cardiovascular risk factors with increasing severity of childhood obesity. Weiss et al12 reported that the prevalence of the metabolic syndrome increased from 38.7% in the moderately obese group to 49.7% in the severely obese group (BMI z score >2.5). In a study of glucose tolerance in overweight children, Sinha et al18 reported that impaired glucose tolerance was detected in 25% of severely obese children and adolescents. Our data on lipid abnormalities detected only a modest increase in the prevalence of abnormal HDL in the severely obese group. However, elevated BP was found in 46.5% of severely obese boys and 39% of severely obese girls compared with 28.1% of boys and 23.1% of girls in the moderately obese groups. Therefore, our data are consistent with other reports that describe an increase in cardiovascular risk factors as severity of obesity increases.
A limitation of this study is the possibility of selection bias because the study sample was based on patients who were referred to a weight management clinic. The range for the BMI z score indicates that our sample includes cases of extreme obesity, which may not be typical of most overweight cases in a clinician's office. Children with increased risk may be more likely to be referred to a weight management program. Elevated BP was found in 34.7% of this overweight clinic sample. This prevalence of elevated BP, however, is consistent with the rate of elevated BP detected in school-based screening of generally healthy high school students reported by Sorof et al,19 in which 34% of adolescents with BMI 95th percentile had high BP. In our study, the plasma lipids were analyzed at different clinical laboratories, which may increase variability. However, the high rates of dyslipidemia found in our sample are comparable to rates of dyslipidemia described in the National Health and Nutritional Examination Survey population data for overweight and are also comparable to the clinical sample of overweight children reported by Weiss et al.12
Another limitation in our study was the inability to analyze the contribution of race to the plasma lipid and BP measurements. TG levels in black men and women are lower than those in white men and women. In both men and women, the mean plasma TG level is reported to be 20 mg/dL lower in black individuals compared with their white counterparts.20 HDL cholesterol levels are higher in black compared with white individuals, a difference that cannot be explained by racial differences in BMI or other factors that have an effect on plasma HDL cholesterol concentration, such as alcohol intake or smoking.21,22 The race of the patients was not consistently recorded in clinical records, thus limiting our ability to examine race effect. Therefore, it is likely that unanalyzed race effects may have contributed to some unevenness in the results on BP and lipid relationships.
The data from this clinical sample of overweight children support the recent recommendation to obtain plasma lipid measures on overweight children with BP 90th percentile.6 Because of the high prevalence of dyslipidemia found in NBP children in this overweight sample, it would be beneficial to obtain plasma lipid measurements on all overweight children, regardless of BP status, as recommended by the American Heart Association.5 Detection of children with multiple risk factors would identify those who require more intense interventions to reduce their cardiovascular risk.
ACKNOWLEDGMENTS
This work was supported in part by National Institutes of Health grants HL51547, DK46107, and HI007845-06.
FOOTNOTES
Accepted Nov 18, 2004.
No conflict of interest declared.
REFERENCES
Ogden CL, Flegel KM, Carroll MD, Johnson CL. Prevalence and trends in overweight among US children and adolescents, 1999–2000. JAMA. 2002;288 :1728 –1732
Gidding S. Relationships between blood pressure and lipids in childhood. Child Hypertens. 1993;40 :41 –49
Reaven G. Role of insulin resistance in human disease. Diabetes. 1988;37 :1595 –1607
Cook S, Weitzman M, Auinger P, Nguyen M, Dietz W. Prevalence of a metabolic syndrome phenotype in adolescents. Arch Pediatr Adolesc Med. 2003;157 :821 –827
Gidding S, Leibel RL, Daniels S, Rosenbaum M, Van Horn L, Marx G. Understanding obesity in youth: a statement for healthcare professionals from the Committee on Atherosclerosis and Hypertension in the Young of the Council on Cardiovascular Disease in Young and the Nutrition Committee, American Heart Association. Circulation. 1996;94 :3383 –3387
National High Blood Pressure Education Program Working Group on High Blood Pressure in Children and Adolescents. The fourth report on the diagnosis, evaluation, and treatment of high blood pressure in children and adolescents. Pediatrics. 2004;114 :555 –576
American Academy of Pediatrics. Committee on Nutrition. Cholesterol in childhood. Pediatrics. 1998;101 :141 –147
National Cholesterol Education Program (NCEP). Highlights of the report of the Expert Panel on Blood Cholesterol Levels in Children and Adolescents. Pediatrics. 1992;89 :495 –501
National High Blood Pressure Education Program Working Group on Hypertension Control in Children and Adolescents. Update on the 1987 Task Force Report on High Blood Pressure in Children and Adolescents: a working group report from the National High Blood Pressure Education Program. Pediatrics. 1996;98 :649 –658
Friedewald WT, Levy RI, Fredrickson DS. Estimation of the concentra-tion of low-density lipoprotein cholesterol in plasma, without use of the preparative ultracentrifuge. Clin Chem. 1972;18 :499 –502
Weiss R, Dziura J, Burgert T, et al. Obesity and the metabolic syndrome in children and adolescents. N Engl J Med. 2004;350 :2362 –2374
Third Report of the National Cholesterol Education Program Expert Panel on Detection, Evaluation and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III). Bethesda, MD: National Heart, Lung, and Blood Institute; 2001
Freedman DS, Dietz WH, Srinivasan SR, Berenson GS. The relation of overweight to cardiovascular risk factors among children and adolescents: the Bogalusa Heart Study. Pediatrics. 1999;103 :1175 –1182
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