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

Seasonal variability in body mass index, waist circumference, and skinfolds in Norwegian children

OBJECTIVES

Studies have shown that children develop a higher body weight during summer months. This has been demonstrated repeatedly using the body mass index (BMI), but the effect of season on other weight-related anthropometric measurements is still unclear.

METHODS

Measurements of height, weight, waist circumference (WC), triceps, and subscapular skinfolds (TSF and SSF), collected from September till May in a cross-sectional sample of 4-16-year-old children and adolescents (n = 4525) from the Bergen Growth Study 1 (BGS1). Differences in z-score by season were tested with linear models adjusted for age group and separately for sex. Overall differences were tested with a one-way between-group analysis of variance.

RESULTS

The girls had higher BMIz (+0.12, p = .03) and WCz (+0.18, p = .002) in fall compared with spring. TSFz (-0.19, p < .001) and SSFz (-0.18, p < .001) were lower in winter in girls, and in boys both in fall (TSFz -0.10, p = .046; SSFz - 0.16, p < .001), and winter (TSFz -0.15, p = .004; SSFz -0.14, p = .003), when compared with spring.

CONCLUSIONS

Seasonal variation was detected for all anthropometric measures, but differences in the direction of the effect between measures of global (BMI), central (WC) or subcutaneous (SF) adiposity suggest a more complex mechanism that needs further exploration.

Associations of social jetlag with physical activity and sedentary behaviour in children and adolescents: A systematic review and meta-analysis

Sleep and daytime movement behaviours occur co-dependently with each other within a finite 24 h day. Sleep parameters other than sleep duration, such as social jetlag and chronotype, have been linked to health problems and unhealthy behaviours among children and adolescents. Given the increasing number of studies examining sleep timing/chronotype and weight-related behaviours, including physical activity and sedentary behaviour, in the past decade, this systematic review and meta-analysis collated and evaluated the evidence on the relationships of social jetlag and chronotype with physical activity and sedentary behaviour among children and adolescents aged 3-17 years. Seven databases were searched on 16 March 2022, and 52 studies were identified as eligible for inclusion, 47 of which were suitable for the meta-analysis. A positive association was found between social jetlag and screen media use (r = 0.14, 95% CI: 0.04-0.24; I2  = 96%; p = 0.008). The morning chronotype was associated with a higher level of physical activity and a lower level of sedentary behaviour than the evening chronotype. No relationship was found between social jetlag and physical activity. The magnitude of heterogeneity among the included studies was high. Further experimental studies are urgently required to understand how circadian preference or misalignment affects activity behaviours. Interventions to promote an active lifestyle in young populations should consider their circadian preference, especially among individuals with the evening chronotype.

Seasonal light hours modulate peripheral clocks and energy metabolism in mice

Except for latitudes close to the equator, seasonal variation in light hours can change dramatically between summer and winter. Yet investigations into the interplay between energy metabolism and circadian rhythms typically use a 12 h light:12 h dark photoperiod corresponding to the light duration at the equator. We hypothesized that altering the seasonal photoperiod affects both the rhythmicity of peripheral tissue clocks and energy homeostasis. Mice were housed at photoperiods representing either light hours in summer, winter, or the equinox. Mice housed at a winter photoperiod exhibited an increase in the amplitude of rhythmic lipid metabolism and a modest reduction in fat mass and liver triglyceride content. Comparing melatonin-proficient and -deficient mice, the effect of seasonal light on energy metabolism was largely driven by differences in the rhythmicity of food intake and not melatonin. Together, these data indicate that seasonal light impacts energy metabolism by modulating the timing of eating.

Seasonal variability in body mass index change among children enrolled in the Pediatric Obesity Weight Evaluation Registry: A step in the right direction

BACKGROUND

Research has shown children disproportionately gain excess weight over the summer months (vs. school months), with stronger effects for children with obesity. However, the question has not been investigated among children receiving care in paediatric weight management (PWM) programs.

OBJECTIVE

To test for seasonal variability in weight change among youth with obesity in PWM care enrolled in the Pediatric Obesity Weight Evaluation Registry (POWER).

METHOD

Longitudinal evaluation of a prospective cohort from 2014 to 2019 among youth in 31 PWM programs. Change in percentage of the 95th percentile for BMI (%BMIp95) was compared by quarter.

RESULTS

Participants (N = 6816) were primarily ages 6-11 (48%), female (54%), 40% non-Hispanic White, 26% Hispanic and 17% Black, and 73% had severe obesity. Children were enrolled on average 424.9 ± 401.5 days. Participants reduced their %BMIp95 every season, but compared with Quarter 3 (July-September), reductions were significantly greater in Q1 (Jan-March, b = -0.27, 95%CI -0.46, -0.09), Q2 (April-June, b = -0.21, CI -0.40, -0.03), and Q4 (October-December, b = -0.44, CI -0.63, -0.26).

CONCLUSION AND RELEVANCE

Across 31 clinics nationwide, children reduced their %BMIp95 every season, but reductions were significantly smaller during the summer quarter. While PWM successfully mitigated excess weight gain during every period, summer remains a high-priority time.

Validation of the Entrainment Signal Regularity Index and associations with children's changes in BMI

OBJECTIVE

This study examined the validity of a novel metric of circadian health, the Entrainment Signal Regularity Index (ESRI), and its relationship to changes in BMI during the school year and summer.

METHODS

In a longitudinal observational data set, this study examined the relationship between ESRI score and children's (n = 119, 5- to 8-year-olds) sleep and physical activity levels during the school year and summer, differences in ESRI score during the school year and summer, and the association of ESRI score during the school year and summer with changes in BMI across those time periods.

RESULTS

The ESRI score was higher during the school year (0.70 ± 0.10) compared with summer (0.63 ± 0.11); t(111) = 5.484, p < 0.001. Whereas the ESRI score at the beginning of the school year did not significantly predict BMI change during the school year (β = 0.05 ± 0.09 SE, p = 0.57), having a higher ESRI score during summer predicted smaller increases in BMI during summer (β = -0.22 ± 0.10 SE, p = 0.03).

CONCLUSIONS

Overall, children demonstrated higher entrainment regularity during the school year compared with the summer. During summer, having a higher entrainment signal was associated with smaller changes in summertime BMI. This effect was independent of the effects of children's sleep midpoint, sleep regularity, and physical activity on children's BMI.

Photoperiodic Remodeling of Adiposity and Energy Metabolism in Non-Human Mammals

Energy homeostasis and metabolism in mammals are strongly influenced by seasonal changes. Variations in photoperiod patterns drive adaptations in body weight and adiposity, reflecting changes in the regulation of food intake and energy expenditure. Humans also show distinct patterns of energy balance depending on the season, being more susceptible to gaining weight during a specific time of the year. Changes in body weight are mainly reflected by the adipose tissue, which is a key metabolic tissue and is highly affected by circannual rhythms. Mostly, in summer-like (long-active) photoperiod, adipocytes adopt a rather anabolic profile, more predisposed to store energy, while food intake increases and energy expenditure is reduced. These metabolic adaptations involve molecular modifications, some of which have been studied during the last years and are summarized in this review. In addition, there is a bidirectional relation between obesity and the seasonal responses, with obesity disrupting some of the seasonal responses observed in healthy mammals, and altered seasonality being highly associated with increased risk of developing obesity. This suggests that changes in photoperiod produce important metabolic alterations in healthy organisms. Biological rhythms impact the regulation of metabolism to different extents, some of which are already known, but further research is needed to fully understand the relationship between energy balance and seasonality.

Seasonality of Children’s Height and Weight and Their Contribution to Accelerated Summer Weight Gain

Background: While children have been shown to have increased BMI during the summer compared to the school year, it is not known if this may be due to seasonal variations in height or weight separately.

Methods: Trained nurses measured heights (cm) and weights (kg) in a cohort of Kindergarteners (n = 7648) twice per year from the beginning of kindergarten through 5th grade. Variation in height and weight by season (school year vs. summer) was examined using separate mixed-effects models. Season, sex, and BMI trajectory group were tested as fixed effects. Random effects included repeated measurements of time, students nested within a school, intercept, and slope for growth over time. Similar models using BMIz as the outcome examined the interaction of height or weight with season.

Results: The rate of height gain was greater during the school year (∼Sept to April) compared to summer (∼April to Sept) (β = -0.05, SE = 0.013, p < 0.0001). The rate of weight gain did not differ seasonally. Height gain was more strongly associated with increased BMIz during summer compared to the school year (β =.02, SE = 0.005, p <0 .0001), mainly among children who remained healthy weight throughout elementary school (β = 0.014, SE = 0.003, p < 0.0001) and those who transitioned to a healthier weight status (β = 0.026, SE = 0.008, p = 0.004). We found a similar seasonal effect for the association between weight with BMIz among children who maintained a healthy weight status (β = 0.014, SE = 0.014, p < 0.0001).

Conclusion: This study indicates seasonality in children’s height gain, gaining height at a faster rate during the school year compared to the summer, while weight gain remained relatively more consistent throughout the year. Seasonality in height and weight gain had the greatest impact on BMIz among children with a healthy weight status. Future research with more frequent measurements is needed to better understand the seasonal regulation of children’s growth and weight gain.

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

OBJECTIVES AND BACKGROUND

Social demands of the school-year and summer environment may affect children's sleep patterns and circadian rhythms during these periods. The current study examined differences in children's sleep and circadian-related behaviors during the school-year and summer and explored the association between sleep and circadian parameters and change in body mass index (BMI) during these time periods.

METHODS

This was a prospective observational study with 119 children ages 5 to 8 years with three sequential BMI assessments: early school-year (fall), late school-year (spring), and beginning of the following school-year in Houston, Texas, USA. Sleep midpoint, sleep duration, variability of sleep midpoint, physical activity, and light exposure were estimated using wrist-worn accelerometry during the school-year (fall) and summer. To examine the effect of sleep parameters, physical activity level, and light exposure on change in BMI, growth curve modeling was conducted controlling for age, race, sex, and chronotype.

RESULTS

Children's sleep midpoint shifted later by an average of 1.5 h during summer compared to the school-year. After controlling for covariates, later sleep midpoints predicted larger increases in BMI during summer, (γ = .0004, p = .03), but not during the school-year. Sleep duration, sleep midpoint variability, physical activity levels, and sedentary behavior were not associated with change in BMI during the school-year or summer. Females tended to increase their BMI at a faster rate during summer compared to males, γ = .06, p = .049. Greater amounts of outdoor light exposure (γ = -.01, p = .02) predicted smaller increases in school-year BMI.

CONCLUSIONS

Obesity prevention interventions may need to target different behaviors depending on whether children are in or out of school. Promotion of outdoor time during the school-year and earlier sleep times during the summer may be effective obesity prevention strategies during these respective times.

Seasonal Variability in Weight Gain Among American Indian, Black, White, and Hispanic Children: A 3.5-Year Study

INTRODUCTION

Several studies have reported that children gain more weight during the summer season. Despite high obesity rates, little research has included American Indian/Alaskan Native children, and few studies have been longitudinal. This observational study examines seasonal weight variability over 3.5 years among ethnically diverse children, including 2,184 American Indian/Alaskan Native children.

METHODS

Children's height and weight were measured before and after the summer from 2012-2015 and analyzed in 2019-2020, including children with ≥2 consecutive measurements (N=7,890, mean age=8.4 [SD=2.8] years). Mixed-effects models tested whether the percentage of the 95th BMI percentile and BMI differed by season (summer versus the rest of the year) and ethnicity.

RESULTS

American Indian/Alaskan Native (23.7%), Hispanic (19.8%), and Black (17.8%) children had significantly higher baseline obesity rates than White children (7.1%). The percentage of the 95th BMI percentile significantly increased during the summer compared with the percentage during the rest of the year, with the strongest effects for children who were obese (b=2.69, 95% CI=1.35, 4.03, p<0.001) or overweight (b=1.47, 95% CI=0.56, 2.35, p<0.01). In BMI units, summer BMI increase was 0.50 kg/m² higher (obese model) and 0.27 kg/m² higher (overweight) than that of the rest of the year. Seasonal effects were significantly less pronounced for American Indian/Alaskan Native children than for White children.

CONCLUSIONS

Children gained significantly more weight during the summer season, with the strongest effects for children who were obese. American Indian/Alaskan Native children had less seasonal variability than White children, but higher overall obesity rates. These data underscore summer as a critical time for obesity prevention among children who are overweight/obese but suggest that seasonal patterns may vary for American Indian/Alaskan Native children.

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

School-aged children gain weight most rapidly in summer, but few studies have investigated summer weight gain among preschool-aged children. We fit continuous linear spline mixed models to test for accelerated summer weight gain among 2,044 children attending 16 Boston-area Head Start programs between fall 2016 and spring 2019. Academic year and summer rates of change in modified body mass index z-score differed (P < .001), with accelerated summer weight gain most pronounced among children with obesity. As with school-aged children, increased focus on the summer is warranted for promoting healthy weight among children in Head Start.