Epidemiology and Causes
of Obesity in Children
DENISE E. WILFLEY
BRIAN E. SAELENS
Obesity in childhood is related to both negative psychosocial consequences and higher rates of obesity-related morbidities in adulthood (see Chapter 85). It frequently persists into adulthood, especially with increasing child age. This chapter examines the epidemiology of childhood obesity as well as commonly proposed etiological factors among children without specific known conditions (e.g., Prader–Willi).
The prevalence of childhood obesity is increasing worldwide (see Chapter 74). Although recent proposals have been advanced, there is no universally accepted definition of childhood obesity. This limits comparative evaluations of prevalence. A method of defining overweight in adults is based on data relating morbidity and mortality to various levels of weight (see Chapter 76). Defining childhood overweight in this manner is problematic because of sparse prospective data to support a classification system. Epidemiological studies have had to rely on statistical definitions of overweight based on selected percentiles for a given reference group (e.g., age and gender).
For population-based assessments, measurements must reflect excess body fat and still be simple to use, standardized, and able to demonstrate comparability across time. Body mass index (BMI) is a weight-for-height index that correlates with adiposity in children and is calculated easily. Commonly used BMI-for-age cut points include ≥ 95th percentile to identify children who are overweight and ≥ 85th and < 95th percentile to identify children at risk for becoming overweight. In children, BMI needs to be assessed using age-specific reference curves, because it changes dramatically with age, compared to