Summary: Teenage girls who experience inadequate sleep have an increased risk of obesity than their peers who prefer to sleep early. Interventions aimed at improving sleep schedules could be useful preventative tools for curbing obesity in teenagers.
Teen girls–but not boys–who prefer to go to bed later are more likely to gain weight, compared to same-age girls who go to bed earlier, suggests a study funded by the National Institutes of Health. The findings by researchers at Kaiser Permanente in Oakland, California, and other institutions appear in JAMA Pediatrics.
A total of 804 adolescents (418 girls and 386 boys) ages 11 to 16 took part in the study. The children responded to questionnaires on their sleep habits and wore an actigraph–a wrist device that tracks movement. Researchers measured their waist size and calculated their proportion of body fat using a technique called dual-energy x-ray absorptiometry. They also estimated the children’s social jet lag–the difference between their weeknight and weekend bedtimes. Those who stayed up far later on weekends than weeknights were considered to have high social jet lag. The authors noted that previous studies had found that adults who preferred to stay up late and had high social jet lag were more likely to gain weight than those who went to be earlier and did not have social jet lag. The researchers undertook the current study to determine if the same associations would be seen in young people.
For girls, staying up later was associated with an average .58 cm increase in waist size and a .16 kg/m2 increase in body fat. Each hour of social jet lag was associated with a 1.19 cm larger waist size and a 0.45 kg/m2 increase in body fat. These associations were reduced–but still remained–after the researchers statistically adjusted for other factors known to influence weight, such as sleep duration, diet, physical activity, and television viewing. Although the researchers found slight associations between these measures and waist size and body fat in boys, they were not statistically significant. The researchers concluded that improving sleep schedules may be helpful in preventing obesity in childhood and adolescence, especially in girls.
Funding: Funding was provided by NIH’s Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institute of Diabetes and Digestive and Kidney Diseases, National Cancer Institute, and National Heart, Lung and Blood Institute.
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Chronotype, social jet lag, and cardiometabolic risk factors in early adolescence
Importance Inadequate sleep duration and quality increase the risk of obesity. Sleep timing, while less studied, is important in adolescents because increasing evening preferences (chronotypes), early school start times, and irregular sleep schedules may cause circadian misalignment.
Objective To investigate associations of chronotype and social jet lag with adiposity and cardiometabolic risk in young adolescents.
Design, Setting, and Participants Starting in 1999, Project Viva recruited pregnant women from eastern Massachusetts. Mother-child in-person visits occurred throughout childhood. From January 23, 2012, to October 16, 2016, 804 adolescents aged 12 to 17 years completed 5 days or more of wrist actigraphy, questionnaires, and anthropometric measurements. A cross-sectional analysis using these data was conducted from April 31, 2018, to May 1, 2019.
Exposures Chronotype, measured via a continuous scale with higher scores indicating greater evening preferences, and social jet lag, measured as the continuous difference in actigraphy sleep midpoint in hours from midnight on weekends vs weekdays, with higher values representing more delayed sleep timing on weekends.
Main Outcomes and Measures Adiposity, measured via anthropometry and dual-energy x-ray absorptiometry. For a subset of 479 adolescents with blood samples, cardiometabolic risk scores were computed as the mean of 5 sex- and cohort-specific z scores for waist circumference, systolic blood pressure, inversely scaled high-density lipoprotein cholesterol, and log-transformed triglycerides and homeostatic model of insulin resistance.
Results Among the 804 adolescents in the study, 418 were girls and 386 were boys, with a mean (SD) age of 13.2 (0.9) years. In multivariable models adjusted for age, puberty, season, and sociodemographics, associations of chronotype and social jet lag with adiposity varied by sex. For girls, greater evening preference was associated with a 0.58-cm (95% CI, 0.12-1.03 cm; P = .04 for interaction) higher waist circumference and 0.16 kg/m2 (95% CI, 0.01-0.31 kg/m2; P = .03 for interaction) higher fat mass index as measured by dual-energy x-ray absorptiometry; each hour of social jet lag was associated with a 1.19-cm (95% CI, 0.04-2.35 cm; P = .21 for interaction) higher waist circumference and 0.45 kg/m2 (95% CI, 0.09-0.82 kg/m2; P = .01 for interaction) higher fat mass index as measured by dual-energy x-ray absorptiometry. Associations of social jet lag and evening chronotypes persisted for many measures of adiposity after adjustment for sleep duration and other lifestyle behaviors. By contrast, no associations were observed in boys. There were no associations with the cardiometabolic risk score for either sex, although statistical power was low for this outcome.
Conclusions and Relevance Evening chronotypes and social jet lag were associated with greater adiposity in adolescent girls but not adolescent boys. Interventions aimed at improving sleep schedules may be useful for obesity prevention, especially in girls.