Body Mass Index
Body Mass Index (BMI) is an indirect way to assess body fat and is calculated by dividing weight by height squared (1). In a clinical setting BMI is a useful tool in assessing children’s weight status, but additional clinical information is useful in making the diagnosis of obesity. For children aged 2 to 20 years, age- and gender-specific references for BMI exist. They were included in the 2000 CDC Growth Charts, which are widely used in clinical practice and are available at www.cdc.gov/growthcharts.
The current recommendation from the American Academy of Pediatrics is to track BMI percentile for children on a yearly basis. The growth curves for children younger than 2 years do not include BMI percentiles, as BMI standards for children in that age group do not exist. Weight-for-height values for these children should be plotted. Intervention and prevention of childhood obesity should begin as early in life as possible. For a more detailed discussion of possible factors and interventions in children's early years, see Perspectives for the Future.
BMI is defined by six categories (Table 1). A child is considered underweight when the BMI < 5th percentile for age and gender. A BMI = 5th percentile and < 85th percentile is considered healthy weight. A child with a BMI > 85th and < 95th percentiles is categorized as overweight; if the BMI = 95th percentile, the child is considered obese. For children younger than 2 years, weight-for-height values above the 95th percentile are classified as overweight. Currently, there are no cutoff points to define obesity in children younger than 2 years.
|BMI < 5th percentile||Underweight|
|BMI 5th-84th percentile||Healthy Weight|
|BMI 85th-94th percentile||Overweight|
|BMI ≥ 95th percentile||Obese|
|BMI ≥ 99th percentile*||Severe Obesity|
|Children < 2 years: Weight-for-height > 95th percentile||Overweight|
*Reported for 5-18 year-olds
The importance of clinically identifying children with severe obesity is increasing, as these children are at particularly high risk for medical and probably psychological complications and may need to be specifically targeted for treatment. Pediatric practitioners can use the 99th percentile BMI cutoff points listed in Table 2. These are not included on the current growth charts.
Table 2. 99th Percentile BMI Cutoff Points According to Age and Gender
Click here for a printable copy of this chart.
|99th Percentile BMI Cutoff Point kg/m2|
Simple formulas can be used to calculate BMI.
Alternatively, an online BMI calculator is available on the CDC website, and BMI wheels have been developed to simplify this calculation for practitioners (order here). It is as important for pediatric practitioners to identify overweight and obese children as it is to recognize patients in whom BMI is increasing. Early intervention is critical for the prevention of childhood obesity. Thus, practitioners are urged to discuss and intervene by proposing nutritional, lifestyle, and behavior modifications for children in whom an upward trend in BMI is noted.
Obese children are at risk for developing numerous obesity-related conditions and medical problems during childhood (Table 3). Additionally, childhood obesity may be an independent risk factor for adult morbidity and mortality, regardless of the persistence of childhood obesity (2). The primary care provider should seek to identify associated comorbidities in each patient. Included in the list of obesity-related conditions are the psychological and social effects on overweight and obese children. These must be investigated thoroughly, as they may often be as damaging as the medical complications.
Type 2 Diabetes Mellitus Particular attention should also be focused on the occurrence of type 2 diabetes mellitus (DM) in children. Type 2 DM is being diagnosed more often in children. Less than a generation ago, type 2 DM was seen almost strictly as an adult disease, with less than 2% of new diabetic cases in children diagnosed as type 2 DM. Today, this number has increased to between 25% and 60% of new-onset childhood diabetics. With obesity being a major risk factor for type 2 DM, pediatric care providers must now view type 2 DM as a pediatric illness (3).
Adapted with permission from the AAP Pediatric Nutrition Handbook.4
Pediatric practitioners also need to have an increased awareness for metabolic syndrome. This syndrome comprises a group of risk factors that indicates an increase in the risk for developing type 2 DM and premature cardiovascular disease in adults (5,6). The concept that insulin resistance and associated metabolic abnormalities, including lipid and blood pressure abnormalities and type 2 DM, increase the risk of atherosclerotic cardiovascular disease in adults was first proposed by Reaven in 1988 at the American Diabetes Association’s annual meeting (7). The metabolic syndrome is known by many names, including syndrome X, insulin resistance syndrome, dysmetabolic syndrome, Reaven’s syndrome, and metabolic cardiovascular syndrome.
Several diagnostic criteria have been proposed for metabolic syndrome, with the two most widely used definitions in adults established by the World Health Organization (WHO) (8) and the U.S. National Cholesterol Education Program (NECP) (9). Table 4 outlines these criteria. Although diagnostic criteria exist for adults, the definition of metabolic syndrome in the pediatric population is nonexistent (10). However, metabolic syndrome in adults has been shown to have its roots in childhood (11). Early recognition and intervention by the pediatrician is therefore critical to the treatment of metabolic syndrome.
Table 4. Diagnostic Criteria of Metabolic Syndrome in Adults
|US National Cholesterol Education Program (NCEP)*||World Health Organization (WHO) †|
|High fasting plasma glucose ≥110mg/dL||Dysglycemia: type 2 diabetes, impaired glucose tolerance, impaired fasting glucose, or insulin resistance|
|Abdominal obesity: waist circumference >40 inches (men) or >35 inches (women)||Obesity in adults, BMI >30 or waist-hip ratio >0.90 (men) or >0.85 (women)|
|Hypertriglyceridemia: TG ≥150 mg/dL||Dyslipidemia: TG ≥ 150 mg/dL, HDL <35 mg/dL (men), HDL <39 mg/dL (women)|
HDL <40 mg/dL (men)
HDL <50 mg/dL (women)
|Hypertension ≥160/90 mm Hg)|
|Blood pressure ≥130/85 mm Hg||Microalbuminuria: urinary albumin excretion rate ≥20 μg/min or albumin/creatinine ratio ≥20 mg/g|
*NCEP: must meet three of five criteria.
†WHO: must meet glucose/insulin criterion and two more.
Hypertension has increased in the pediatric population, in part because of the increase in childhood obesity. Unlike hypertension in adults, hypertension in children is not defined by an established cutoff point. Like BMI, the definition of childhood hypertension is defined based upon the normative distribution of blood pressure in healthy children. Blood pressure percentiles are based on gender, age, and height. Hypertension is diagnosed after elevated measurements are noted on three separate occasions. Here are blood pressure reference tables for both boys and girls .
The guidelines for the definition of normal and elevated blood pressures in children were updated in 2004 and are included below. The systolic and diastolic blood pressures are of equal importance. If there is a disparity between the two, the higher value determines the blood pressure category. Blood pressure categories are defined as: 1) Normal Blood Pressure: Systolic and diastolic blood pressure < 90th percentile 2) Prehypertention: Systolic and/or diastolic blood pressure ≥ 90th but < 95th percentile, or if the blood pressure exceeds 120/80 mmHg even if < 90th percentile. A systolic pressure of 120 typically occurs at 12 years of age, although a diastolic pressure of 80 typically occurs at 16 years of age. 3) Stage 1 Hypertension: Systolic and/or diastolic blood pressure between the 95th and 99th percentiles plus 5 mm Hg 4) Stage 2 Hypertension: Systolic and/or diastolic blood pressure ≥ 99th percentile plus 5 mm Hg (12).
1) Normal Blood Pressure: Systolic and diastolic blood pressure < 90th percentile
2) Prehypertention: Systolic and/or diastolic blood pressure ≥ 90th but < 95th percentile, or if the blood pressure exceeds 120/80 mmHg even if < 90th percentile. A systolic pressure of 120 typically occurs at 12 years of age, although a diastolic pressure of 80 typically occurs at 16 years of age.
3) Stage 1 Hypertension: Systolic and/or diastolic blood pressure between the 95th and 99th percentiles plus 5 mm Hg
4) Stage 2 Hypertension: Systolic and/or diastolic blood pressure ≥ 99th percentile plus 5 mm Hg (12).
5. Laaksonen DE, Lakka HM, Niskanen LK, Kaplan GA, Salonen JT, Lakka TA. Metabolic syndrome and the development of diabetes mellitus: application and validation of recently suggested definitions of the metabolic syndrome in a prospective cohort study. Am J Epidemiol. 2002;156(11):1070-1077.
8. Alberti KG, Zimmet PZ. Definition, diagnosis, and classification of diabetes mellitus and its complications: Part 1. Diagnosis and classification of diabetes mellitus. Report of a WHO consultation. Diab Med. 1998;15:539-553.
9. Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults. Executive summary of the Third Report of The National Cholesterol Education Program (NCEP) Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel Ill.) JAMA. 2001;285(19):2486-2497.
12. National High Blood Pressure 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(2 suppl 4th report):555-576.