Identifying Patterns of BMI Development and Associated Behavioral, Social, Environmental, Genetic, and Biological Factors for Children from 3-10 Years

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Summer (i.e., May-August) is a period of accelerated BMI gain that leads to increases in childhood obesity. Two theories may explain accelerated summer BMI gain. The Circadian and Circannual Rhythm Model (CCRM) posits that BMI gain during summer is biologically driven by the shifting light-dark cycle, with BMI gain accelerating during the summer when days are longer and weight gain outpaces height gain and decelerating during the winter when days are shorter and height gain outpaces weight gain. The Structured Days Hypothesis (SDH) proposes that accelerations in BMI gain during the summer are due to the removal of the structured school day (i.e., school vs no school during summer) which influences children’s engagement in key obesogenic behaviors (physical activity, sedentary/screen time, dietary intake, and sleep). Breaks throughout the school year (1-week fall break, 2-week winter break, 1-week spring break) may also cause accelerated BMI gain. Current accelerated BMI gain research is focused exclusively on summer vs. school year comparisons. These studies measure children in the spring (May prior to summer) and fall (August following summer) exclusively, allowing only for comparisons of BMI gain between the 3 months of summer and the other 9 months of the year. It does not allow for the measure of decelerations in BMI gain predicted by the CCRM during the winter, nor does it allow for the measure of accelerations in BMI gain during the fall, winter, and spring breaks predicted by the SDH. This is a critical limitation in our understanding of WHEN childhood obesity occurs and HOW to treat it. This study will overcome these limitations by identifying monthly patterns in the accelerations and decelerations of children’s height, weight, and BMI gain and the associated behavioral, social, environmental, and biological determinates. We will recruit 3 cohorts (3K, Kindergarten, and Second grade) of 200 children (600 children in total) to participate in a cohort-sequential design. We will collect BMI monthly; obesogenic behaviors (physical activity, sedentary/screen time, dietary intake, and sleep) in the spring, summer, fall, and winter; and social, environmental, and biological information over three years for each cohort. The cohort-sequential design will allow us to map BMI development and seasonal shifts in behaviors 3K to 5th grade. We will accomplish the following specific aims: Aim 1: Identify monthly variations in height, weight, and BMI change in a large and diverse cohort of children (3K to 5th grade, N=600). Aim 2: Examine the relationship between monthly patterns of height, weight, and BMI change with seasonal (fall, winter, spring, summer) patterns in obesogenic behaviors. Aim 3 Exploratory: Examine the relationship of social, environmental, and biological factors with patterns in behaviors and variations in height, weight, and BMI z-score change. This project is significant because it fills a major gap (monthly patterns of BMI z-score gain) in the knowledge about the development of childhood obesity, a widespread public health crisis. This project is innovative because it will be among the first studies to measure BMI gain monthly along with the associated behavioral, social, environmental, and biological determinates that predict accelerated/decelerated BMI gain.