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

Authors: MORENO, JENNETTE - Children'S Nutrition Research Center (CNRC); RAZJOUYAN, JAVAD - Baylor College Of Medicine; LESTER, HOUSTON - Baylor College Of Medicine; DADABHOY, HAFZA - Children'S Nutrition Research Center (CNRC); AMIRMAZAHERI, MONA - Baylor College Of Medicine; REESOR-OYER, LAYTON - University Of South Carolina; O'CONNOR, TERESIA - Children'S Nutrition Research Center (CNRC); HERNANDEZ, DAPHNE - University Of Texas Health Science Center; NAJAFI, BIJAN - Baylor College Of Medicine; ALFANO, CANDICE - University Of Houston; CROWLEY, STEPHANIE - Rush University Medical Center; Thompson, Deborah - Debbe; BARANOWSKI, TOM - Children'S Nutrition Research Center (CNRC)

Submitted to: International Journal of Behavioral Nutrition and Physical Activity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/25/2021
Publication Date: 7/12/2021
Citation: Moreno, J.P., Razjouyan, J., Lester, H., Dadabhoy, H., Amirmazaheri, M., Reesor-Oyer, L., O'Connor, T.M., Hernandez, D.C., Najafi, B., Alfano, C.A., Crowley, S.J., Thompson, D.J., Baranowski, T. 2021. Later sleep timing predicts accelerated summer weight gain among elementary school children: A prospective observational study. International Journal of Behavioral Nutrition and Physical Activity. 18:94. https://doi.org/10.1186/s12966-021-01165-0.
DOI: https://doi.org/10.1186/s12966-021-01165-0

Interpretive Summary: In order to determine if differences in children's sleep during the school year and summer contributes to differences in weight gain during the summer than during the school year, 119 children in Kindergarten through 2nd grade, ages 5 to 8 years old were studied. Children's heights and weights were measured at the beginning and end of the 2016-2017 school year and again at the beginning of the 2017-2018 school year. Differences in children's sleep, activity, and exposure to outdoor light during the school year and summer was measured with an accelerometer (a device worn on the wrist, similar to a Fitbit). The timing of children's sleep shifted later by an average of 1.5 hours during summer compared to the school-year. Later sleep timing during summer predicted greater increases in child's BMI during summer. Spending more time exposed to outdoor light was associated with smaller increases in BMI during the school year. 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.

Technical Abstract: 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. 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. 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, (y=.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, y=.06, p=.049. Greater amounts of outdoor light exposure (y=-.01, p=.02) predicted smaller increases in school-year BMI.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.