Open Access Highly Accessed Research article

Summer effects on body mass index (BMI) gain and growth patterns of American Indian children from kindergarten to first grade: a prospective study

Jianduan Zhang12*, John H Himes1, Peter J Hannan1, Chrisa Arcan1, Mary Smyth1, Bonnie Holy Rock1 and Mary Story1

Author Affiliations

1 Division of Epidemiology and Community Health, School of, Public Health, University of Minnesota, 1300 South 2nd Street, Suite 300, Minneapolis, MN 55454, USA

2 Department of Maternal and Children Care and Adolescent Health, School of Public Health, Huazhong University of Science and Technology, Wuhan, Hubei, China 430030

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BMC Public Health 2011, 11:951  doi:10.1186/1471-2458-11-951

Published: 23 December 2011



Overweight and obesity are highly prevalent among American Indian children, especially those living on reservations. There is little scientific evidence about the effects of summer vacation on obesity development in children. The purpose of this study was to investigate the effects of summer vacation between kindergarten and first grade on growth in height, weight, and body mass index (BMI) for a sample of American Indian children.


Children had their height and weight measured in four rounds of data collection (yielded three intervals: kindergarten, summer vacation, and first grade) as part of a school-based obesity prevention trial (Bright Start) in a Northern Plains Indian Reservation. Demographic variables were collected at baseline from parent surveys. Growth velocities (Z-score units/year) for BMI, weight, and height were estimated and compared for each interval using generalized linear mixed models.


The children were taller and heavier than median of same age counterparts. Height Z-scores were positively associated with increasing weight status category. The mean weight velocity during summer was significantly less than during the school year. More rapid growth velocity in height during summer than during school year was observed. Obese children gained less adjusted-BMI in the first grade after gaining more than their counterparts during the previous two intervals. No statistically significant interval effects were found for height and BMI velocities.


There was no indication of a significant summer effect on children's BMI. Rather than seasonal or school-related patterns, the predominant pattern indicated by weight-Z and BMI-Z velocities might be related to age or maturation.

Trial registration

Bright Start: Obesity Prevention in American Indian Children Clinical Trial Govt ID# NCT00123032

American Indian; children; body mass index; summer vacation