Lifestyle choices in the 21st century are frequently centered on individual and family activities of expediency, rather than sound diets and wellness, and have resulted in an obesogenic (environmental conditions that encourage excess weight gain) and chronic disease culture that is responsible for the deteriorating health in today's children. An example of a chronic disease observed in today's children related to this culture is the metabolic syndrome. To assess the interactive relationships for the risk factors of the metabolic syndrome, we have developed a theoretical model (Figure 1) of how these factors influence each other and contribute to cardiovascular disease. The model indicates that glucose intolerance/insulin resistance and obesity are two risk factors that contribute directly and indirectly, through their relationship with the other three risk factors, to cardiovascular disease. The other risk factors contribute directly to cardiovascular disease. To better understand these relationships, the focus of this article will be to define the metabolic syndrome in children; discuss the impact of and the difficulty assessing childhood obesity; the relationships among obesity, lipoproteins, and glucose; the relationships among blood pressure and other metabolic syndrome risk factors; and procedures that help in managing the metabolic syndrome.
DEFINITION OF THE METABOLIC SYNDROME IN CHILDREN
The metabolic syndrome is the clustering of metabolic risk factors and has gone by several different names over the years: syndrome X, insulin resistance syndrome, prediabetes, metabolic syndrome, dysmetabolic syndrome, plurimetabolic syndrome, cardiometabolic syndrome, dyslipidemic hypertension, and hypertriglyceridemic waist (1). It was initially called insulin resistance (type 2 diabetes) syndrome because it developed from insulin resistance that resulted in compensatory excess insulin in the blood that was frequently triggered by obesity (2). Because type 2 diabetes was once thought of as adulthood onset of diabetes, the metabolic syndrome in children has only recently been identified, and there still is no universally accepted definition for children (3).
Defining the metabolic syndrome in children is difficult because of constant body changes associated with maturation. The definition developed by Sarah de Ferranti, M.D., M.P.H., and colleagues in the Department of Cardiology at the Children's Hospital in Boston, Massachusetts, will be the reference for pediatric metabolic syndrome discussions in this article. They define pediatric metabolic syndrome as the clustering of three or more of the following conditions in a child: fasting triglycerides greater than or equal to 100 mg/dL, high-density lipoprotein cholesterol (HDL-C) less than or equal to 50 mg/dL, fasting glucose greater than or equal to 110 mg/dL, waist circumference greater than the 75th percentile for age and sex, and systolic blood pressure greater than the 90th percentile for sex, age, and height. The definition takes into consideration maturation and was designed for adolescents, but has use for younger children (4).
IMPACT OF AND DIFFICULTY OF ASSESSING OBESITY
The obesogenic culture that causes obesity not only affects the physical health of children, it also impacts them socially, educationally, and financially. Juhee Kim, Sc.D. (5), at the Harvard University School of Public Health concludes that independent of baseline socioeconomic status and performance on aptitude tests, overweight and obese adolescents are less likely to marry, complete fewer years of school, and are more likely to be poor as adults. Lifestyle choices that include chronic patterns of poor diets and physical inactivity will cause major health problems and may have the greatest overall impact on the quality of life in the United States during the next three or four decades (5).
According to data from the National Health and Nutrition Examination Survey III (6), in the last few decades, childhood obesity has tripled to a prevalence of greater than 15% (5). Obesity can be viewed as a root disease (one from which a number of others develop) because health problems presently associated with obesity were essentially nonexistent 15 to 20 years ago.
Because of poor lifestyle choices such as decreased physical activity, consuming large quantities of fast foods that often are fried and lacking in nutritional content, and sedentary entertainment, such as television viewing and playing video games, many children today are developing the preculture for type 2 diabetes as young as 6 or 7 years (7). This trend has a negative impact on childhood wellness and will grow larger if not addressed with proactive healthy lifestyle choices.
Overweight and obesity increased 120% in African American and Hispanic children, and 50% in white children from 1986 to 1998. Overweight and obesity have continued to increase; currently, one in seven children and adolescents in the United States is overweight or obese (8,9). Estimates of overweight and obesity in children are not based on body fat measurements, but typically are based on body mass index (BMI), which is the amount of weight per unit of height. The overweight classification for children is a BMI greater than or equal to the 85th percentile to less than or equal to 95th percentile for age and sex, and obesity is a BMI greater than the 95th percentile for age and sex. Caution should be used when determining the clustering of overweight and obesity measured by BMI with other metabolic conditions, and this is especially true when children of different racial backgrounds are evaluated. For example, African American children have more dense skeletons and may have a different lean body tissue composition for a given unit of height than white children matched by age and sex. A BMI at the 85th percentile for an African American child may provide different clustering relationships with other metabolic syndrome conditions than for a white child (10,11).
RELATIONSHIPS OF OBESITY WITH LIPOPROTEINS AND GLUCOSE
When children are evaluated for metabolic syndrome based on BMI classifications, a higher coronary heart disease risk profile is observed for total cholesterol (TC), HDL-C, and low-density lipoprotein cholesterol (LDL-C) in boys with BMI values greater than the 95th percentile. For the girls, only triglycerides are higher for those with the higher BMI values. These data clearly indicate that the relationships of BMI with blood lipoproteins and lipids for boys are different from girls. Greater clustering of blood lipoproteins and lipids with BMI seems to occur in the boys (12).
Dr. Ribeiro and colleagues (12) at the University of Porto, Portugal, report that most children (62% of boys and girls) at risk for obesity are more likely to experience other metabolic syndrome risk factors. Work in other laboratories supports this finding because overweight and obesity are reported to be associated with type 2 diabetes, hypertension, lipid abnormalities, and pulmonary obstructive diseases (8).
In a metabolic study, an obese group and a control group of children aged 6 to 14 years underwent an oral glucose tolerance test and were measured for plasma glucose, insulin levels, insulin sensitivity, and insulin resistance as evaluated by mathematical modeling. Obese children were found to have significantly higher blood pressure (systolic and diastolic), triglycerides, TC, LDL-C, and lower HDL-C (good cholesterol) than normal-weight children. Plasma glucose levels during the oral glucose tolerance test were similar in both obese and control children, whereas plasma insulin levels were significantly higher in obese children. Insulin sensitivity and glucose utilization rates were lower in the obese. In summary, obesity impacts many of the other metabolic syndrome risk factors in children (12).
RELATIONSHIP BETWEEN BLOOD PRESSURE AND OTHER METABOLIC SYNDROME CONDITIONS
Metabolic syndrome risk factors all contribute to cardiovascular disease but seem to make direct and/or indirect contributions through influence on other risk factors in children. In a study of 497 children between 2 and 18 years, blood lipids, blood pressure, and obesity were assessed. The children were evaluated for the influence of blood pressure, and obesity on blood lipids and lipoproteins. When the children were divided into normal and prehypertensive-hypertensive groups based on sex, more boys had HDL-C values less than 40 mg/dL, and more girls had LDL-C values greater than or equal to 130 mg/dL. These results suggest that lipids and blood pressure make independent contributions to cardiovascular disease risks in children (11).
To assess the impact of elevated blood pressure during childhood on hypertension and the metabolic syndrome later in life, 493 children with elevated blood pressure were followed over several decades. Odds ratios of developing hypertension and the metabolic syndrome were computed for each individual at different stages of development during their lives. The results indicated that boys who were hypertensive at age 5 to 7 years were more than three times as likely to be hypertensive as adults. Girls with hypertension at age 8 to 13 years were almost twice as likely to develop hypertension as nonhypertensive girls. Younger boys and girls with elevated blood pressures are more than twice as likely to develop the metabolic syndrome once they become adults (13).
Results from data on 11-year-old African American boys and girls in our laboratory were generally consistent with results published in the literature (10,11). The boys and girls were measured for body composition, TC, HDL-C, and glucose, and the variables were evaluated for relationships with each other (Figure 2). The results indicate that blood lipoproteins and glucose share low but similar relationships (r ≤ 0.40) with body composition as measured by both BMI and percent body fat estimated from skinfolds. However, when BMI increased, there also was a trend for an increase in TC and glucose. The relationships between blood pressure and body composition variables are significant and similar for BMI and percent body fat in the children. Unlike lipoproteins and glucose, which seem to each make a significant independent contribution to the development of cardiovascular disease in children, blood pressure shares a significant relationship with body fat and BMI. This suggests that the contribution blood pressure makes to the development of cardiovascular disease is shared with or influenced by body composition in children.
MANAGING THE METABOLIC SYNDROME IN CHILDREN
Recent data suggest that in children with the metabolic syndrome, healthy lifestyle modifications should include weight loss, regular physical activity, and careful monitoring of the individual metabolic syndrome risk factors. Treatments should be based on behavior changes designed to optimize lifestyle modifications. A realistic goal for weight reduction is 7% to 10% of body weight. However, weight loss interventions with children should be undertaken with care because growth and development are necessary parts of maturation and may complicate achieving desirable reduction in weight. Thus, body composition assessments are helpful tools for managing the obesity aspect of the metabolic syndrome in children (5,14).
Children who are sedentary should begin with low-intensity exercise for relatively short periods and gradually increase the length of participation during each session. For example, a child could begin with a comfortable 10-minute walk and increase the time over a 2- or 3-week period. Children should be encouraged to reduce time spent participating in sedentary activities and to develop more physically active lives by walking up stairs, walking to events, and participating in lifetime physical activities such as those listed in the Table. Physical activity is not only associated with successful weight reduction, but also can help reduce the progression to diabetes in children with the metabolic syndrome.
Children and adolescents in the lowest quartile for physical activity have more metabolic syndrome risks, such as insulin resistance and low HDL-C, than children in the highest quartile (5). Children should be encouraged to participate in a variety of physical activities, thus creating a more conducive environment for regular participation.
Endurance, resistance, and lifetime physical activities such as those listed in the Table should be part of the menu. Physical activity recommendations should include practical, regular, and moderate regimens of exercise, with a daily minimum participation time of 30 to 60 minutes. There seems to be a dose-response between physical activity participation and the metabolic syndrome. Children who exercise at heart rates of about 150 BPM (roughly 6 METS) have reduced metabolic syndrome risk factors. Therefore, health and fitness professionals who find creative ways of encouraging children to participate in physical activity at the recommended duration and intensity will contribute greatly to metabolic syndrome management (15).
Healthy diets for children with family histories or who are at risk for the metabolic syndrome also are effective interventions (5). Recommended dietary intake for these children include at least five fruits and vegetables a day; increased consumption of whole grains; avoidance of sweets, sodas, and other empty-calorie foods; and a dietary fat content of no more than 30% of total calories per day. These guidelines can be found online at www.health.gov/dietaryguidelines/dga2000/document/frontcover.htm.
It is important when dealing with children to determine if there is an underlying condition causing high blood pressure and design a treatment of that condition. Obesity and overweight are risk factors that contribute to a rise in blood pressure across all age groups. This is especially dangerous for children because studies show that overweight children with high blood pressure are much more likely to become adult heart disease patients. Other conditions that may contribute to high blood pressure include kidney disease and endocrine disorders (11,13).
SUMMARY AND CONCLUSIONS
Health and fitness professionals are knowledgeable of physical activity participation and weight loss regimens, and can play an important role in managing the metabolic syndrome in children. Similar to adults, this article indicates that obesity and insulin resistance are the backbone of the metabolic syndrome in children because both influence cardiovascular disease directly and indirectly through other risk factors. In recent years, the obesogenic culture experienced by many children has become a major contributor to the metabolic syndrome. Elevated childhood blood pressure has been shown to be an effective predictor of the metabolic syndrome later in life because it is associated with abnormal blood lipids and lipoproteins.
Recognizing the relationships among the risks factors and devoting efforts to control each risk factor is an important step in reducing the prevalence of the metabolic syndrome in children. In addition to the above interventions, changing behaviors so that children participate more frequently in lifetime physical activities and consume healthier diets will alter the obesogenic culture and help minimize or eliminate the growth of this disease in children.
CONDENSED VERSION AND BOTTOM LINE
The metabolic syndrome is a fairly new health issue for children that can be effectively managed with healthy lifestyle choices such as physical activity, balanced diets, and frequent checkups.
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