Physiological mechanisms underlying children's circannual growth patterns and their contributions to the obesity epidemic in elementary school age children

Abstract

Several studies since the 1990s have demonstrated that children increase their body mass index at a faster rate during summer months compared with the school year, leading some to conclude that the out-of-school summer environment is responsible.Other studies, however, have suggested that seasonality may play a role in children's height and weight changes across the year. This article reviews evidence for seasonal differences in the rate of children's height and weight gain and proposes potential physiological mechanisms that may explain these seasonal variations.

Later sleep timing predicts accelerated summer weight gain among elementary school children: a prospective observational study

“…The CCR Model of accelerated summer weight gain proposed that the lack of social demands during summer would result in more variable sleep timing, which may increase the risk of circadian misalignment during summer contributing to accelerated summer weight gain [26,27]. However, the current study found no evidence of school-summer differences in the variability of sleep timing and there was no association of variability in sleep timing with children's change in BMI during the school year or summer.…”

“…The effect of age was allowed to vary across participants and controlled for differences in the number of days between BMI assessments across participants. Variables were selected a priori for inclusion in the model based on theory [26,27] and previous research demonstrating differences in children's sleep across sex [55], race [56], age [57], and chronotype [58].…”

“…The Circadian and Circannual Rhythms Model (CCR Model) of accelerated summer weight gain, proposed that in the absence of the social demands of the school year (e.g., school schedules and sleep related parenting practices), children would exhibit changes in behavior such as shortened sleep duration, later and more variable sleep timing, and reduced PA [26,27]. It was hypothesized that reductions in PA reduce the amplitude of the circadian system and sleep/wake homeostasis, thereby reducing the pressure to sleep at night [28,29].…”

“…Lower levels of PA may also affect circadian rhythmicity through decreased exposure to natural light, as increased PA is associated with greater outdoor light exposure [30][31][32]. These changes in behaviors may affect synchronization of circadian and circannual rhythms by affecting children's exposure to the light/dark cycle and contributing to a blunting of circadian rhythmicity which may contribute to accelerated weight gain [26,27,33]. According to the CCR Model children's sleep timing, duration, and variability, PA, and light exposure represent novel pathways which may differentially influence children's BMI during the school year and summer.…”

Summer Weight Gain Among Preschool-Aged Children With Obesity: An Observational Study in Head Start

“…Similar patterns have been observed among school-aged children ( 1 ) and in 2 previous studies of preschoolers ( 2 , 4 ), adding to the evidence that efforts to promote healthy child weight may be most needed in summer. The lack of a structured daily schedule ( 10 ), the biological response to longer day length ( 11 ), or both may explain accelerated summer weight gain. However, more research is necessary among preschool-aged children, because another study found a decrease in BMIz over the summer among preschool-aged children with obesity ( 3 ).…”