Original Article

Obesity

PEDIATRIC OBESITY

Seasonal Variability in Weight Change During Elementary School Jennette P. Moreno1, Craig A. Johnston1,2, Tzu-An Chen1, Teresia A. O’Connor1, Sheryl O. Hughes1, Janice Baranowski1, Deborah Woehler3, and Tom Baranowski1

Objective: To examine seasonal variation in weight gain across elementary school (kindergarten-5th grade) among children who are healthy weight, overweight, or obese and from different racial and ethnic groups. Methods: The sample included 7,599 ethnically diverse students ages 5-7 years at baseline (Caucasian: 21.1%, Black: 36.2%, Hispanic: 26.0%, Asian 16.7%). Heights and weights were measured by school nurses at the beginning and end of each school year from kindergarten through the beginning of 5th grade. Results: Beginning the summer after 1st grade, all children demonstrated a pattern of standardized BMI (zBMI) increases during the summer (0.04 to 0.09) and zBMI decreases across the school years (20.06 to 0.00; P < 0.0001). Hispanic children and children who were overweight and obese exhibited this pattern in kindergarten while children of other ethnicities and with a healthy weight did not (P < 0.0001). Conclusions: Beginning the summer after 1st grade, a consistent pattern of relative weight gain during the summer months (D in BMI percentile 5 1.04) and weight loss during the school year (D in BMI percentile 5 20.34) emerged. This pattern appeared earlier for children who were overweight, obese, or Hispanic. These findings suggest a need to better understand the causes of the problematic increases in weight during the summer. Obesity (2015) 23, 422–428. doi:10.1002/oby.20977

Introduction Currently, about 16% of school age children 6- to 11-years old are overweight and 18% are obese (1). Obese children are at increased risk for obesity in adulthood (2,3) and developing associated health problems (4-7). Obese children are also more likely to experience weight-related teasing and bullying, increasing their risk for developing low self-esteem and other negative psychological consequences (8). Although the cause of pediatric obesity is multifactorial (9), the school environment has received considerable attention for its impact on children’s weight (10). Significant weight gain occurs among children during the elementary school years, contributing to the increasing prevalence of overweight and obesity in children ages 6- to 11-years old (11-14). Sub-

stantial increases in body mass index (BMI) percentile have been demonstrated between 1st and 3rd grades (11); between 1st and 7th grades (14); and over a 5-year period in 4th, 5th, and 6th grade students (12). Obesity in elementary school significantly increased children’s risk of being overweight in the future (15,16). However, children in these studies were not tracked across all elementary school years (11) nor tracked regularly (i.e., at the beginning and end of each school year) (15,16). This limits the ability to determine the critical times in elementary school when the rate of weight gain significantly increased. Consistent evidence suggests that considerable weight gain in elementary school occurs during the summer months (17-21). This pattern of seasonal weight gain has been demonstrated in both the United States and Japan (17-21). Differences in school year and

1 USDA/ARS Children’s Nutrition Research Center, Department of Pediatrics–Nutrition, Baylor College of Medicine, Houston, Texas, USA. Correspondence: Jennette P. Moreno ([email protected]) 2 Department of Medicine, Baylor College of Medicine, Houston, Texas, USA 3 The Oliver Foundation, Houston, Texas, USA.

Funding agencies:The authors would like to thank The Oliver Foundation for its support. This work also has had been funded, in part, with federal funds from the USDA/ ARS under Cooperative Agreement No. 58-6250-6001. Disclosure: The authors declared no conflict of interest. Author contributions: Dr. Moreno and Dr. Johnston have full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis. Study concept and design: Johnston, Woehler. Analysis and interpretation of data: Moreno, Johnston, Chen, T. Baranowski, Hughes, O’Connor, J. Baranowski. Drafting of the manuscript: Moreno, Johnston, Chen. Critical revision of the manuscript for important intellectual content: Moreno, Johnston, Chen, T. Baranowski, Hughes, O’Connor, J. Baranowski, Woehler. Statistical analysis and preparation of tables and figures: Chen. Study supervision: Johnston, Woehler. Received: 12 August 2014; Accepted: 26 October 2014; Published online 31 December 2014. doi:10.1002/oby.20977

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Obesity | VOLUME 23 | NUMBER 2 | FEBRUARY 2015

www.obesityjournal.org

Original Article

Obesity

PEDIATRIC OBESITY

TABLE 1 Characteristics of participants (means 6 s.d. or %)

Variable Age at baseline (years) Gender (% female) Race and ethnicity White Black Hispanic Asian Initial weight category Healthy weight Overweight/obese School Title I status Title Ie Non-Title I

Overall samplea (N 5 7,599)

Baseline sampleb (n 5 3,588)

Sample missing baseline datac (n 5 4,011)

Sample with complete datad (n 5 1,597)

5.7 6 0.3 48.9

5.7 6 0.3 48.7

NA 49.4

5.7 6 0.3 50.2

21.1 36.2 26.0 16.7

27.2 29.0 26.4 17.4

15.5 42.9 25.6 16.0

32.0 23.0 23.1 21.9

66.9 33.1

70.2 29.8

64.0 36.0

71.6 28.4

18.6 81.4

38.8 61.2

43.9 56.1

27.5 72.5

a

The overall sample includes all children who provided data. The baseline sample includes only participants present at baseline. The sample missing baseline data includes those who were either missing during the baseline data collection or matriculated into the 2005 kindergarten cohort after baseline. d The sample with complete data provided height and weight measurements at all time points. e Title I status indicates that at least 40% of students come from low-income families. b c

summer environments may impact weight gain in elementary school age children (17). The pattern of summertime weight gain has been observed in children as young as 5-years old (18,21), although a similar study with American Indian children failed to confirm these findings (22). Divergent seasonal weight gain patterns have been observed between children who are healthy weight and overweight and obese (19) and mixed results have been found when examining differences across ethnic groups (17,21). However, no studies have examined seasonal patterns of weight gain longitudinally throughout elementary school. Examining children’s weight gain longitudinally across time is crucial to determining children’s weight gain trajectories (23). Additionally, no studies have examined seasonal patterns of weight gain longitudinally across weight status categories, gender, racial/ethnic groups, and socioeconomic (SES) levels. Understanding critical stages when significant weight gain is likely to occur may inform obesity prevention efforts (24). For example, if the majority of weight gain is driven by increases that occur during the summer months in early elementary school, then obesity interventions targeting the prevention of summertime weight gain in early elementary school may be most successful. In addition, understanding if these trends are consistent across racial and ethnic groups, gender, SES, and weight status categories may assist with further targeting interventions. We previously demonstrated in a longitudinal sample that elementary school aged children who were healthy weight, overweight, or obese at baseline tended to gain weight during the summer months, but not during the school months (17). The current study adds to this by examining yearly seasonal variation in weight gain across 5 years in elementary school among 1) children who are healthy weight, overweight, or obese at baseline, 2) different racial and ethnic groups of children, 3) gender, and 4) SES. Examination of when

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the pattern of seasonal fluctuation in weight gain emerges and whether it remains consistent over time for children of different classifications will aid in the identification of key time periods in which to focus preventive weight gain interventions among various groups.

Methods Study population The sample included 7,866 students from a Southeast Texas independent school district, which included 41 elementary schools (17). Baseline measurements were conducted with students enrolled in the kindergarten class of 2005 (n 5 3,734). Students not present at baseline and children who matriculated into the 2005 kindergarten cohort were included in subsequent data collections (n 5 4,132). Underweight and American Indian children were excluded from analyses due to limited sample size (at baseline: 136 underweight, 10 American Indian; Following baseline: 110 underweight, 11 American Indian) resulting in an overall and baseline sample of 7,599 students and 3,588 kindergarten students, respectively. A total of 1,597 students had complete standardized BMI (zBMI) data at all time points. Sample characteristics are presented in Table 1. The sample of 7,599 was included in these analyses.

Procedure School records regarding students’ gender and ethnicity were provided to researchers by the school district. The researchers were not given access to records about whether students qualified for free or reduced price lunch, thus Title I status was used as a proxy for school level SES. Fifteen elementary schools were designated as Title I schools indicating 40% or more of students were from lowincome families (25).

Obesity | VOLUME 23 | NUMBER 2 | FEBRUARY 2015

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Obesity

Weight Change During Elementary School Moreno et al.

School nurses measured children’s heights and weights twice annually in the fall (end of August-beginning of October) and spring (end of March-beginning of May) of each school year. Tanita Accustat stadiometers were installed in all schools and schools were provided with a Tanita HD-351 Digital scale. Heights and weights were obtained using the digital scale and stadiometer with the children wearing light clothing and no footwear. The training of nurses has been described elsewhere (17). Data were collected as administrative data which the school district allowed the researchers to use anonymously. This study was approved by the school district and the Institutional Review Board of Baylor College of Medicine. BMI was calculated (weight (lb)/[height (in)]2 3 703) and translated into a zBMI and percentile using gender and age normative data from the Center for Disease Control and Prevention (CDC) (26). Children’s height, weight, sex, and age at measurement were used to calculate zBMI scores; conversion was performed using the SAS program provided by the CDC (27). Based on baseline BMI percentiles, children were classified into 1 of 4 weight categories: underweight (

Seasonal variability in weight change during elementary school.

To examine seasonal variation in weight gain across elementary school (kindergarten-5th grade) among children who are healthy weight, overweight, or o...
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