Heights were measured using 1 of 2 methods, depending on the practice ’s preference; either with a measuring arm attached to a wall or with a measuring arm attached to a scale. All measuring arms were checked to be certain they were parallel to the floor. Weights were taken on balance beam scales calibrated less than a month before the study began. Patients removed their coats and shoes; no weight adjustments were made for clothing. Each office nursing staff reviewed the measuring procedures before participating in the study. Trained on-site study coordinators (office managers or nursing managers) supervised the data gathering process to ensure adherence.
The University Committee on Research Involving Human Subjects of Michigan State University approved our study protocol.
Definitions of Obesity in Children and Adolescents
There is no internationally accepted measure to define obesity in children. Methods for classifying childhood and adolescent obesity have been developed on the basis of comparison with growth charts (percentile weight for height by age and sex), percentile of triceps skin fold thickness, and percentile cutoffs for body mass index (BMI). BMI is emerging as the prefer red standard. The Expert Committee on Clinical Guidelines for Overweight in Adolescent Preventive Services8 recommends that children and adolescents with a BMI greater than the 85th percentile but less than the 95th be classified as “at risk of overweight” and those with a BMI greater than the 95th percentile be classified as “overweight.” We used that classification system.
For the comparisons, we followed the method used by Troiano.1 For the baseline standard, he used the BMI distributions derived from the National Health Examination surveys (NHES II for children aged 6 to 11 years and NHES III for children aged 12 to 17 years). He calculated the percentage of children above the 85th and 95th percentile cutoffs of NHES for NHANES I, NHANES II, and NHANES III data. Similarly, we calculated the percentage of children and adolescents in the Michigan primary care practices with BMIs greater than the 85th and 95th percentiles as defined by NHES. For a contemporary regional comparison group, we obtained data from the Kuntzelman Fitness for Youth Program (KFYP), a 1997 statewide survey of Michigan schoolchildren. In that survey, a nonrandom sample of schoolchildren from 41 Michigan school districts were weighed and measured. Because 90% of our primary care patients were white, we used only the data on white children from the KFYP database. We summarized the KFYP data in the same way as the other surveys.
Results
A total of 993 children aged 4 to 17 years were measured and weighed in the Michigan primary care practices. There were 502 boys and 491 girls. Of these patients, 90% were white; 3% were Native American; 3% were African American; 1% was Hispanic; 1% was of another race; and 2% did not state their race. The Table 1 shows the percentage of children in the Michigan primary care practices above the 85th and 95th percentiles based on the NHES data and compared with NHANES data and Michigan schoolchildren (KFYP). The prevalences of obesity in the United States have increased over time, and the patients in our primary care practices have the highest prevalences of obesity in all age and sex groups when compared with the national surveys. For example, for boys aged 6 to 11, the percentage of those overweight in NHANES was 11%, whereas 20% of the Michigan primary care patients in this age group were overweight. In all groups, except for girls aged 6 to 11 years, prevalences of obesity of the primary care patients were greater than those of the Michigan schoolchildren in the KFYP survey.
Discussion
A larger than expected proportion of the children and adolescents in our primary care practices in Michigan are at risk for being overweight or are overweight. The prevalences of obesity in children and adolescents presenting for care in these practices are nearly 2 times greater than the national prevalences measured in NHANES II and NHANES III an d somewhat greater than a contemporary sample of Michigan schoolchildren. The absolute prevalences of obesity in the children and adolescents seen in our primary care practices were 3% to 9% higher than in the Michigan schoolchildren in all age-sex categories, except for girls aged 6 to 11 years.
It is not surprising that obesity is more prevalent in our sample than in the NHANES II and NHANES III surveys; NHANES data was gathered from 1976 to 1980 and 1988 to 1994, respectively, and obesity prevalences are steadily increasing. However, the reason that our patients are more obese than a contemporary sample of Michigan schoolchildren is unknown. The difference may be caused by systematic bias, as neither of the surveys was based on random sampling. However, in the analysis of our adult patients, the prevalence of obesity of patients was much greater than local community prevalences, even after adjusting for socioeconomic status and medical conditions known to be associated with obesity.8