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.
