A new study by US scientists has found that children grow faster during the school year than during the summer, as published in the journal & #39;Frontiers in Physiology’.
It has long been known that children in Western countries are more likely to be overweight or obese during the summer. Among the causes are changes in children’s physical activity and diet during the summer period, including summer vacations.
Researchers have now shown that since Body Mass Index (BMI) is the ratio of body weight in kg to height in meters squared, faster vertical growth during the course leads to to an increase in BMI during the summers.
“Here “We show seasonality in standardized body mass index (BMIz), with children gaining height at a higher rate during the school year compared to the summer,” explains Dr. Jennette P. Moreno, Assistant Professor, USDA/ARS Children’s Nutrition Research Center, Baylor College of Medicine, and first author of the study.
BMIz is individual BMI scaled to mean BMI It is population-specific, such that a BMIz of one is equivalent to a BMI one standard deviation above the mean. Typically, a BMIz of 1.04 is considered overweight, and a BMIz of 1.64 obesity.
“Children’s rate of weight gain was more consistent than their rate of height gain throughout the year, except among children who began to transition to an unhealthy weight status in the summer after finishing second grade,” explains Moreno.
Moreno and his colleagues statistically reanalyzed the results of their 2013 study, in which they followed 3,588 children who entered kindergarten in September 2005, in any of the 41 schools in the School District. Independent from Fort Bend, around the city of Sugar Land, Texas.
They followed these children, who were between five and six years old at the beginning, until the fall of what followed at the end of the fourth grade of primary school, five years later. The nurses measured each child’s height and weight twice a year, in mid-September and mid-April. The present reanalysis is more powerful than the 2013 one.
The authors divided the children into five “BMI trajectory groups,” based on their pattern of change in BMIz throughout the study. In this case, 22.6% of the children scored as ‘overweight or chronic obesity’, 8.2% as ‘weight becoming healthy’, 8.5% as ‘early onset overweight or obese’
Early onset was defined as as the transition to above-average BMIz beginning in the summer after kindergarten, and late onset as the onset of this transition in the summer after second grade.
In addition to BMI trajectory group and season (fall or spring), the authors used school, child’s age in months, gender, race, or ethnicity. and body weight or relative height compared to peers as explanatory variables to model seasonal changes in height, weight, and BMIz, as well as weight. as their modifier stat interactions.
Vertical growth was seasonal: the height of the children increased faster during the school year than during the summer, with a mean rate difference of 0.055 cm/month. As a result, plots of linear growth over time – corrected for other variables – show an irregular pattern, with peaks in spring and troughs in autumn.
This deficit in vertical growth through the summer was greater for those “chronically obese or overweight”, with a total of approximately -0.1 cm/month less growth through the summer than through the course school.
The rate of weight gain did not differ between seasons. However, the latest combined patterns of height and weight made BMIz higher in summer, while the probability of being overweight or obese increased. considerably during every summer.
“Although the pattern of height gain shows a greater increase in height during the school year, the increase in height of the children influenced the height gain. BMIz increased more strongly during the summer vacation year than during the school year, and weight gain showed This is a steady increase during the school year,” says co-author Debbe Thompson, MD, USDA/ARS research nutritionist and professor in the USDA/ARS Children’s Nutrition Research Center in the College of Medicine. Baylor.
“This differential seasonal impact of height and weight on BMIz leads to a healthier BMIz state during the school year,” he adds.
What causes the strong seasonality of vertical growth is not yet clear. Sure. “It is possible that the demands of the school year alter children’s exposure to the daily light-dark cycle, which may cause the seasonal pattern in altitude. Further studies of children who are in school year-round may help answer this question,” says final author Dr. Craig A Johnston, associate professor in the Department of Health and Human Performance from the University of Houston.
” Clearly, children at higher risk for overweight and obesity have a less pronounced seasonal impact of height gain on BMIz, indicating that they would benefit from obesity prevention efforts throughout the year. year,” concludes Johnston.