News Release 

Chronotype, social jet lag associated with higher waist size, fat mass in adolescent girls

JAMA Pediatrics

Bottom Line: For adolescent girls but not boys, bigger waistlines and greater fat mass were associated with being an evening chronotype who prefers going to bed and waking up later and greater social jet lag because of later sleep timing on weekends versus weekdays, independent of sleep duration and other lifestyle factors. This observational study of 804 adolescents (418 girls and 386 boys; average age 13) from eastern Massachusetts included data from wrist monitors, questionnaires and body measurements. Chronotype was measured based on a scale with higher scores indicating evening versus morning preferences for adolescents; social jet lag was the difference in sleep midpoint in hours from midnight on weekends (free days) versus weekdays (school days) with higher values meaning that sleep timing shifted later on free days. There were no associations with a cardiometabolic risk score. A limitation of the study is that causal inferences cannot be made about the associations. The findings suggest that obesity prevention efforts should consider regular patterns of sleep and wake times, in addition to more and better-quality sleep.

Author: Elizabeth M. Cespedes Feliciano, Sc.D., Sc.M., of Kaiser Permanente Northern California, Oakland, and coauthors


Editor's Note: The article contains conflict of interest and funding/support disclosures. Please see the article for additional information, including other authors, author contributions and affiliations, financial disclosures, funding and support, etc.


Media advisory: To contact corresponding author Elizabeth M. Cespedes Feliciano, Sc.D., Sc.M., email Janet Byron at or Mckenzie Ridings at The full study and editorial are linked to this news release.

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