Teenage girls who prefer to go to bed late are more likely to gain weight compared to same-age girls who go to bed earlier warn researchers. For the study published in the journal JAMA Pediatrics a total of 804 adolescents -- 418 girls and 386 boys aged between 11 to 16 -- were analysed. The children responded to questionnaires on their sleep habits and wore an actigraph - a wrist device that tracks movement said researchers from the Kaiser Permanente a healthcare company in the US. During the study the research team measured the participants' waist size and calculated their