The Third National Health and Nutrition Examination Survey, 1988-1994(NHANES III) revealed that 11.5% of adolescents were obese. The NHANES III sample size for Mexican Americans was small.
To determine the prevalence of adolescent obesity in a South Texas population that is preponderantly low-income Mexican Americans.
Cross-sectional prevalence study.
All secondary school campuses of one rural independent school district with a low-income Mexican American population.
Four thousand three hundred seventy-five students, aged between 12 and 17 years, enrolled in 4 secondary school campuses of 1 Rio Grande Valley, South Texas, independent school district for academic year 1998-1999.
Main Outcome Measures
Body mass index (BMI) was calculated for all 4375 students using weights and heights measured by school nurses on enrollment. Each student's BMI was then plotted on a sex-specific chart and the percentile range for age was determined. Those within the 85th to the 95th percentile were classified as at risk for obesity and those above the 95th percentile were classified as obese.
Of 2149 adolscent girls and 2226 adolescent boys, 18% were at risk for obesity and 22.1% were obese. A total of 40.1% had a BMI at the 85th percentile or higher for age and sex. The prevalence of obesity also continues to rise even after puberty more markedly in adolescent girls than adolescent boys. Furthermore, the mean BMI progressively increases with age and is generally at the 85th percentile or higher.
Our data revealed a much higher prevalence rate of obesity in this adolescent Mexican American population than the rate obtained in NHANES III. It is even higher than the rate specific for Mexican American adolescents in NHANES III. The NHANES III significantly underestimates the prevalence of adolescent obesity in preponderantly impoverished Mexican American adolescents. This consequently leads to underestimation of the public health risks as well as the present and future cost of health care associated with obesity in this population.
IT IS a well-recognized fact that over the last 2 decades the prevalence of obesity in the United States has significantly increased. Several surveys have also documented a similar trend internationally.1,2
Data from the Third National Health and Nutrition Examination Survey, 1988-1994 (NHANES III)3 revealed an increase of 22% for 6- to 19-year-olds with a body mass index ([BMI], calculated as the weight, in kilograms, divided by the height, in meters, squared) above the 85th percentile for age and sex from 15% in NHANES II. Overweight or obesity was defined as a BMI above the 95th percentile for age and sex. At risk for obesity has been defined as within the 85th and 95th percentiles. [The terms "overweight" and "obesity" are used interchangeably here.] Of the adolescents sampled, ages 12 to 17 years, 11.5% were overweight, representing a 6% increase nationwide in adolescent obesity from NHANES II data. The prevalence rates specific to Mexican Americans were even higher at 14.8% for adolescent boys and 13.7% for adolescent girls.2- 4 The NHANES III, however, had a relatively small sample for Mexican American adolescents.
We were concerned because South Texas, and the Rio Grande Valley in particular, already has one of the highest rates in the country for type 2 diabetes mellitus in adults and mortality from cardiovascular causes.5 The goal of the study was to determine the prevalence of adolescent obesity in the local population of the Rio Grande Valley which is preponderantly low-income Mexican Americans.
A cross-sectional prevalence study was performed involving the students enrolled in the 4 secondary schools comprising the secondary division of one rural South Texas independent school district, for academic year 1998-1999. This included 2 junior high schools, 1 ninth grade campus, and 1 high school. The total enrollment for this academic year was 4774; data were taken from all students. The ethnic population of the 4 schools was homogeneous with the following composition: 95.6% Mexican Hispanic, 4.1% white, 0.2% black, and 0.1% Asian or Pacific Islander. It was also fairly homogeneous for socioeconomic status, with 78.9% falling below the 1998 federal poverty level. Three thousand eight hundred sixty-two students (80.9%) belonged to families designated as economically disadvantaged, defined by an annual family income of 185% or less of the federal poverty level. This is the cutoff for eligibility for free school meals. Furthermore, a substantial number, 16.2%, of the students were members of migrant seasonal farmworker families.
On registration for the school year, trained school nurses measured and recorded each student's weight, height, sex, and age at the time of screening. The BMI was calculated for each student using the standard formula. Each value was then plotted on the sex-specific chart6 and the BMI percentile range was determined. Each student was then classified as obese (≥95th percentile for age and sex), at risk (85th-95th percentile), or normal (<85th percentile).7,8 Our data from the adolescents aged 12 to 17 years were also analyzed separately for comparison with NHANES III data.
Of a total of 4375 12- to 17-year-old students screened, 2149 (49%) were girls and 2226 (51%) were boys (Table 1). One thousand seven hundred fifty-five or 40.1% of the 12- to 17-year-olds in this independent school district had a BMI at or above the 85th percentile for age and sex.
In Figure 1, the average BMI is plotted against the age in years. For each age group there was an average of approximately 700 subjects. The average BMI was noted to increase progressively with age. At age 12 years, the average BMI for adolescent boys is 22.7 and for adolescent girls 22.5. At age 16 years, the average BMI has risen to 24.9 in adolescent boys and 24.7 in adolescent girls. At almost all points, the average BMI for age is at or above the 85th percentile. An exception occurred in the 15-year-old girls, the mean BMI was skewed by the presence of a few very thin girls.
Average body mass index (BMI) vs the age of the students enrolled in 4 secondary schools campuses of 1 Rio Grande Valley, South Texas, independent school district in academic year 1998-1999. For each age group there was an average of approximately 700 subjects. The numbers are the average body mass index for that age- and sex-specific chart.
Table 2 gives the average BMI and height for age; Figure 2 plots these values. Adolescent girls were noted to reach the adult height of approximately 1.57 m (62 in) at about 15 years of age; the adolescent boys reach the adult height of about 1.70 m (67 in) at 16 to 17 years of age. The BMI, however, shows a continued increase even after puberty in both sexes, but more dramatically in adolescent girls.
Average body mass index (BMI) and the average height vs age by sex for students enrolled in 4 secondary school campuses of 1 Rio Grande Valley, South Texas, independent school district in academic year 1998-1999.
The link between adult obesity and other conditions, such as type 2 diabetes mellitus and hypertension, has long been established.9- 12 Women with low-income or low-educational levels are also more likely to be obese than those of higher socioeconomic status although this association is less consistent in men.4 The children in our independent school district are nearly all in the lower socioeconomic group. Furthermore, it has also been established that childhood obesity is a risk factor for adult obesity, with children obese at age 12 years having more than a 70% likelihood of remaining obese as adults.7,11,12 Body mass index in adolescents correlates with markers of secondary complications of obesity including current blood pressure, blood lipid levels, blood lipoprotein levels, and long-term mortality.8
Many of the adolescents in this independent school district seem to have the same poor dietary and exercise habits as most teenagers. Owing to the heat, the amount of juice drinks and sugar-containing cola soft drinks consumed per day is enormous, adding a lot of hidden calories to the daily diet. The school lunches have been compliant with US dietary guidelines providing 30% or less of the calories from fat. In a recent survey of our Women, Infants, and Children program infants, we also found that 24% of 4102 2- to 3-year-olds were higher than the 85th percentile for weight. Thus, in some children, the problem with weight may begin even prior to starting school.
The current recommendation from the Expert Committee convened in 1997 by the Maternal and Child Health Bureau, Health Resources and Services Administration, and the Department of Health and Human Services is that children with a BMI at or above the 85th percentile with complications of obesity or with a BMI at or above the 95th percentile, with or without complications, undergo evaluation and possible treatment.8 Obesity is not considered a billable disease under current Texas Medicaid reimbursement.
In NHANES III, the prevalence rate of obesity for the total sample of adolescents aged 12 to 17 years was 11.5%, and 22% for a BMI at or above the 85th percentile.2,3 Our data from a larger sampling of a homogeneous preponderantly Mexican American population reveals rates much higher than these and higher even than the NHANES III rates specific for Mexican American adolescent boys and girls. In our study, there was a 6.9% difference in the prevalence rate of obesity in local adolescent girls over the Mexican American girls in the NHANES III (20.6% vs 13.7%) and a 9.9% difference over all adolescent girls (10.7%). There was also an 8.8% difference in the prevalence rate of obesity in local adolescent boys over Mexican American boys in the NHANES III (23.6% vs 14.8%) and an 11.2% difference over all adolescent boys (12.4%).2,4
The findings from our study suggest that NHANES III significantly underestimates the prevalence of adolescent obesity in a preponderantly low-income Mexican American population. This results in an underestimate of the health risks and health care costs of the epidemic of obesity and its consequences, namely, cardiovascular disease, syndrome X (obesity with hypertension, dyslipidemia, acanthosis nigricans, and early atherosclerotic changes), and type 2 diabetes mellitus.
We thus encourage health care professionals among high-risk populations to be particularly vigilant and comprehensive during health care maintenance visits of children and adolescents for evaluation of obesity and risk for obesity. Early active intervention is crucial if we are to control this burgeoning disaster. Unfortunately, however, weight loss is still generally difficult to achieve and recidivism is high.13 Prevention, then, remains the most viable method for controlling obesity and must begin early in life.
Accepted for publication April 12, 2000.
This study was funded in part by the Children's Heart and Health Institute of South Texas, Corpus Christi, Pfizer Committed to Kids, New York, NY, and the American Academy of Pediatrics CATCH Planning Funds program, Elk Grove Village, Ill.
Presented at the 1999 annual meeting of the Pediatric Academic Societies, San Francisco, Calif, May 3, 1999.
We gratefully acknowledge the assistance of Ana Salina, RN, Lilia Guerrero, RN, Elizabeth Parker, LVN, and the other staff members of the the independent school district Secondary Schools Health Services.
Corresponding author/reprints: Edanili Lacar, MD, Nuestra Clinica del Valle, Mission Family Health Center, 1018 N Conway, Mission, TX 78572.
Lacar ES, Soto X, Riley WJ. Adolescent Obesity in a Low-Income Mexican American District in South Texas. Arch Pediatr Adolesc Med. 2000;154(8):837-840. doi:10.1001/archpedi.154.8.837