Causes of Childhood Obesity

Childhood obesity has more than tripled in the past 30 years. The prevalence of obesity among children aged 6 to 11 years increased from 6.5% in 1980 to 19.6% in 2008. The prevalence of obesity among adolescents aged 12 to 19 years increased from 5.0% to 18.1%.

Obesity is the result of caloric imbalance (too few calories expended for the amount of calories consumed) and is mediated by genetic, behavioral, and environmental factors.  Childhood obesity has both immediate and long-term health impacts:

• Obese youth are more likely to have risk factors for cardiovascular disease, such as high cholesterol or high blood pressure. In a population-based sample of 5- to 17-year-olds, 70% of obese youth had at least one risk factor for cardiovascular disease.
• Children and adolescents who are obese are at greater risk for bone and joint problems, sleep apnea, and social and psychological problems such as stigmatization and poor self-esteem.
• Obese youth are more likely than youth of normal weight to become overweight or obese adults, and therefore more at risk for associated adult health problems, including heart disease, type 2 diabetes, stroke, several types of cancer, and osteoarthritis.

Healthy lifestyle habits, including healthy eating and physical activity, can lower the risk of becoming obese and developing related diseases.

Obesity is a serious health concern for children and adolescents. Results from the 2007-2008 National Health and Nutrition Examination Survey (NHANES), using measured heights and weights, indicate that an estimated 17 percent of children and adolescents ages 2-19 years are obese. Between 1976-1980 and 1999-2000, the prevalence of obesity increased. Between 1999-2000 and 2007-2008 there was no significant trend in obesity prevalence.

Among pre-school age children 2-5 years of age, obesity increased from 5 to 10.4% between 1976-1980 and 2007-2008 and from 6.5 to 19.6% among 6-11 year olds.  Among adolescents aged 12-19, obesity increased from 5 to 18.1% during the same period.

Obese children and adolescents are at risk for health problems during their youth and as adults. For example, during their youth, obese children and adolescents are more likely to have risk factors associated with cardiovascular disease (such as high blood pressure, high cholesterol, and Type 2 diabetes) than are other children and adolescents.

Obese children and adolescents are more likely to become obese as adults.  For example, one study found that approximately 80% of children who were overweight at aged 10–15 years were obese adults at age 25 years.  Another study found that 25% of obese adults were overweight as children.  The latter study also found that if overweight begins before 8 years of age, obesity in adulthood is likely to be more severe.

Body mass index (BMI) is a practical measure used to determine overweight and obesity. BMI is a measure of weight in relation to height that is used to determine weight status. BMI can be calculated using either English or metric units. BMI is the most widely accepted method used to screen for overweight and obesity in children and adolescents because it is relatively easy to obtain the height and weight measurements needed to calculate BMI, measurements are non-invasive and BMI correlates with body fatness.6 While BMI is an accepted screening tool for the initial assessment of body fatness in children and adolescents, it is not a diagnostic measure because BMI is not a direct measure of body fatness.Use of BMI to Screen for Overweight and Obesity in Children

For children and adolescents (aged 2–19 years), the BMI value is plotted on the CDC growth charts to determine the corresponding BMI-for-age percentile.

• Overweight is defined as a BMI at or above the 85th percentile and lower than the 95th percentile.
• Obesity is defined as a BMI at or above the 95th percentile for children of the same age and sex.

These definitions are based on the 2000 CDC Growth Charts for the United States and expert committee.7 A child’s weight status is determined based on an age- and sex-specific percentile for BMI rather than by the BMI categories used for adults. Classifications of overweight and obesity for children and adolescents are age- and sex-specific because children’s body composition varies as they age and varies between boys and girls.

Architectural and Interior Design Solutions for Preventing Childhood Obesity in Schools

Prevalence of High Body Mass Index in US Children and Adolescents, 2007-2008
Cynthia L. Ogden; Margaret D. Carroll; Lester R. Curtin; Molly M. Lamb; Katherine M. Flegal
JAMA. 2010;303(3):242-249
The prevalence of high weight for length or high body mass index (BMI) among children and teens in the U.S. (i.e., at or above the 95th percentile), ranges from approximately 10 percent for infants and toddlers, to approximately 18 percent for adolescents and teenagers, although these rates appear to have remained relatively stable over the past 10 years, except for an increase for 6- to 19-year-old boys who are at the very heaviest weight levels, according to a CDC study appearing in the January 20 issue of JAMA.

At the individual level, childhood obesity is the result of an imbalance between the calories a child consumes as food and beverages and the calories a child uses to support normal growth and development, metabolism, and physical activity. In other words, obesity results when a child consumes more calories than the child uses. The imbalance between calories consumed and calories used can result from the influences and interactions of a number of factors, including genetic, behavioral, and environmental factors.¹⁰ It is the interactions among these factors – rather than any single factor – that is thought to cause obesity.¹¹

Studies indicate that certain genetic characteristics may increase an individual’s susceptibility to excess body weight.^{12, 13} However, this genetic susceptibility may need to exist in conjunction with contributing environmental and behavioral factors (such as a high-calorie food supply and minimal physical activity) to have a significant effect on weight. Genetic factors alone can play a role in specific cases of obesity . For example, obesity is a clinical feature for rare genetic disorders such as Prader-Willi syndrome.¹⁴ However, the rapid rise in the rates of overweight and obesity in the general population in recent years cannot be attributed solely to genetic factors. The genetic characteristics of the human population have not changed in the last three decades, but the prevalence of obesity has tripled among school-aged children during that time.^{8, 46}

Because the factors that contribute to childhood obesity interact with each other, it is not possible to specify one behavior as the “cause” of obesity . However, certain behaviors can be identified as potentially contributing to an energy imbalance and, consequently, to obesity .

• Energy intake: Evidence is limited on specific foods or dietary patterns that contribute to excessive energy intake in children and teens. However, large portion sizes for food and beverages, eating meals away from home, frequent snacking on energy-dense foods and consuming beverages with added sugar are often hypothesized as contributing to excess energy intake of children and teens.¹⁵In the area of consuming sugar-sweetened drinks, evidence is growing to suggest an association with weight gain in children and adolescents.^{16, 17, 18} Consuming sugar-sweetened drinks may be associated with obesity because these drinks are high in calories.¹⁹ Children may not compensate at meals for the calories they have consumed in sugar-sweetened drinks, although this may vary by age.^{20, 21} Also, liquid forms of energy may be less satiating than solid forms and lead to higher caloric intake.^{22, 23}
• Physical activity: Participating in physical activity is important for children and teens as it may have beneficial effects not only on body weight, but also on blood pressure and bone strength.²⁴Physically active children are also more likely to remain physically active throughout adolescence and possibly into adulthood.²⁵
  Children may be spending less time engaged in physical activity during school. Daily participation in school physical education among adolescents dropped 14 percentage points over the last 13 years — from 42% in 1991 to 28% in 2003.  In addition, less than one-third (28%) of high school students meet currently recommended levels of physical activity.
• Sedentary behavior: Children spend a considerable amount of time with media. One study found that time spent watching TV, videos, DVDs, and movies averaged slightly over 3 hours per day among children aged 8–18 years. Several studies have found a positive association between the time spent viewing television and increased prevalence of obesity in children. Media use, and specifically television viewing, may
  • displace time children spend in physical activities,
  • contribute to increased energy consumption through excessive snacking and eating meals in front of the TV,
  • influence children to make unhealthy food choices through exposure to food advertisements,¹⁵and
  • lower children’s metabolic rate.

Home, child care, school, and community environments can influence children’s behaviors related to food intake and physical activity.

• Within the home: Parent-child interactions and the home environment can affect the behaviors of children and youth related to calorie intake and physical activity. Parents are role models for their children who are likely to develop habits similar to their parents.
• Within child care: Almost 80% of children aged 5 years and younger with working mothers are in child care for 40 hours a week on average. Child care providers are sharing responsibility with parents for children during important developmental years. Child care can be a setting in which healthy eating and physical activity habits are developed.
• Within schools: Because the majority of young people aged 5–17 years are enrolled in schools and because of the amount of time that children spend at school each day, schools provide an ideal setting for teaching children and teens to adopt healthy eating and physical activity behaviors. According to the Institute of Medicine (IOM), schools and school districts are, increasingly, implementing innovative programs that focus on improving the nutrition and increasing physical activity of students.
• Within the community: The built environment within communities influences access to physical activity opportunities and access to affordable and healthy foods. For example, a lack of sidewalks, safe bike paths, and parks in neighborhoods can discourage children from walking or biking to school as well as from participating in physical activity. Additionally, lack of access to affordable, healthy food choices in neighborhood food markets can be a barrier to purchasing healthy foods.

Childhood obesity is associated with various health-related consequences. Obese children and adolescents may experience immediate health consequences and may be at risk for weight-related health problems in adulthood.

Some consequences of childhood and adolescent obesity are psychosocial. Obese children and adolescents are targets of early and systematic social discrimination. The psychological stress of social stigmatization can cause low self-esteem which, in turn, can hinder academic and social functioning, and persist into adulthood.

Obese children and teens have been found to have risk factors for cardiovascular disease (CVD), including high cholesterol levels, high blood pressure, and abnormal glucose tolerance. In a population-based sample of 5- to 17-year-olds, 70% of obese children had at least one CVD risk factor while 39% of obese children had two or more CVD risk factors.

Less common health conditions associated with increased weight include asthma, hepatic steatosis, sleep apnea and Type 2 diabetes.

• Asthma is a disease of the lungs in which the airways become blocked or narrowed causing breathing difficulty. Studies have identified an association between childhood obesity and asthma.
• Hepatic steatosis is the fatty degeneration of the liver caused by a high concentration of liver enzymes. Weight reduction causes liver enzymes to normalize.
• Sleep apnea is a less common complication of obesity for children and adolescents. Sleep apnea is a sleep-associated breathing disorder defined as the cessation of breathing during sleep that lasts for at least 10 seconds. Sleep apnea is characterized by loud snoring and labored breathing. During sleep apnea, oxygen levels in the blood can fall dramatically. One study estimated that sleep apnea occurs in about 7% of obese children.
• Type 2 diabetes is increasingly being reported among children and adolescents who are obese.  While diabetes and glucose intolerance, a precursor of diabetes, are common health effects of adult obesity, only in recent years has Type 2 diabetes begun to emerge as a health-related problem among children and adolescents.Onset of diabetes in children and adolescents can result in advanced complications such as CVD and kidney failure.