By Nicole MacKee
Regular sleep-wake schedules, in addition to longer sleep duration and improved sleep quality, may assist in preventing obesity in adolescents, particularly girls, US researchers have reported.
A cross-sectional study, published in JAMA Pediatrics, investigated the impact of chronotype and ‘social jet lag’ (the sleep midpoint difference between weekend nights and weekday nights) on the adiposity and cardiometabolic risk of 804 adolescents (418 girls and 386 boys) aged 12 to 17 years.
The researchers used questionnaires to collect data on chronotype and wrist actigraphy to measure social jet lag.
They found that among girls evening chronotype (a preference for later sleep and wake times) was associated with a 0.58 cm higher waist circumference and 0.16 kg/m2 higher fat mass index. They also found that each hour of social jet lag was associated with a 1.19 cm higher waist circumference and a 0.45 kg/m2 higher fat mass index in girls. No such associations were found in boys, and no links with cardiometabolic risk scores were found.
Dr Danielle Longmore, Paediatric Endocrinologist at Melbourne’s Royal Children’s Hospital, said the study built upon known associations between reduced sleep and increased adiposity and obesity in children, adolescents and adults, and was likely to be applicable in Australia. She pointed to similar findings in an Australian study of children’s sleep onset and obesity risk (Sleep 2011; 34: 1299-1307). Dr Longmore said the fact that the significant outcomes in the US study were seen in girls, but not in boys, may be due to ‘complex and as yet undetermined factors’, and more research was needed in this area.
‘Differences in sex hormones between males and females may influence metabolic outcomes and result in the differences seen,’ she said. ‘The difference in adiposity outcomes between males and females may also be influenced by ... psychosocial factors, such as anxiety, depression, differences in behaviours or differences in diet or meal timing that accompany the sleep changes in females.’
The US researchers reported that chronotype associations were ‘slightly attenuated’ after adjustment for sleep duration, whereas many of the associations with social jet lag persisted despite adjustment for sleep duration, diet quality, physical activity and television viewing.
Dr Longmore said it was unclear if the data collected on TV viewing included all screen time.
‘Increasingly, adolescents spend a great deal of time on a phone or other smart device, particularly in the evening, which may impact sleep onset and quality,’ she said.
Dr Longmore said the findings underlined the importance of asking young people more detailed questions about sleep.
‘Duration is important; however, this study gives further support that the timing of onset and social jetlag are important factors also,’ Dr Longmore told Endocrinology Today.
JAMA Pediatr 2019; doi: 10.1001/jamapediatrics.2019.3089.