Shorter, More Variable Sleep Duration Linked to Greater Metabolic Risk in Children

Shorter sleep duration and more variable sleep patterns, particularly on weekends, are linked to greater metabolic risk in children, according to the results of a cross-sectional study reported online January 24 in Pediatrics.

"Associations between short sleep duration, obesity and metabolic dysfunction have been proposed for children but have not been explored appropriately", write Karen Spruyt, PhD, from Comer Children's Hospital and Pritzker School of Medicine, University of Chicago, Illinois, and colleagues. "...The goal was to explore the effects of duration and regularity of sleep schedules on [Body Mass Index (BMI)] and the impact on metabolic regulation in children."

In this study, 308 children aged 4 to 10 years were recruited from the community and underwent measurement of BMI. Wrist actigraphs allowed determination of sleep patterns for 1 week. A subsample of participants also underwent measurement of fasting morning plasma level of glucose, insulin, lipids and high-sensitivity C-reactive protein.

Regardless of whether their weight was in the normal, overweight or obese category, participants had average sleep duration of 8 hours per night, which was markedly below the current recommendations. There was a nonlinear trend between sleep duration and weight. Obese children had shorter and more variable sleep duration on weekend than on school days, whereas overweight children had a mixed sleep pattern.

High variance in sleep duration and short sleep duration tended to be associated with changes in insulin, low-density lipoprotein and high-sensitivity C-reactive protein plasma levels. The greatest health risk was in children with sleep patterns at the lower end of sleep duration, especially when sleep schedules were irregular.

"The main findings included a nonlinear trend between sleep duration and body weight ad the finding that the children's sleep averaged 8 hours per night regardless of body weight", the study authors write. "Lower sleep duration values were strongly associated with increased metabolic risk."

Limitations of this study include short duration of actigraphy; lack of data on visceral and subcutaneous fat amounts; blood samples only obtained in only 36,6% of children and use of a predominantly white, non-Hispanic sample, which could have limited generalizability to other racial or ethnic groups.

"Obese children were less likely to experience 'catch-up' sleep on weekends, and the combination of shorter sleep duration and more variable sleep patterns was associated with adverse metabolic outcomes", the study authors conclude. "Educational campaigns, aimed at families, regarding longer and more regular sleep may promote decreases in obesity rates and may improve metabolic dysfunction trends in school-aged children."

Clinical Context
Inadequate sleep might affect neuropeptide regulation of appetite, leading to greater food intake and obesity, as reported by Zheng and Berthoud in the April 2008 issue of Physiology. However, in children, the effects of sleep pattern on BMI and metabolic dysfunction are not known. This community-based cohort study assesses sleep duration and the association between sleep pattern and BMI and metabolic dysfunction in children.

Study Highlights 

• 308 children aged 4 to 10 years were recruited from a public school system in Kentucky.
• Exclusion criteria were chronic medical conditions, generic craniofacial syndromes and neurobehavioral disorders.
• Mean age of the children was 7.2 years.
• 51% were girls.
• 71.4% were white, 18.8% were black and 9.7% were of other race or ethnicity.
• Weight and height were measured to determine BMI.
• Overweight was defined as a BMI z score of more than 1.04, and obesity was defined as a BMI z score of 1.65 or higher.
• Each child wore an actigraphs device for 1 week to determine sleep-and-awake intervals based on activity counts.
• Mean total sleep time was calculated for 7 consecutive days, school days (Sunday through Thursday) and weekends (Friday and Saturday).
• 132 children underwent fasting morning plasma tests for levels of glucose, insulin, triglycerides, lipids and high-sensitivity C-reactive protein.
• The median respiratory disturbance index was higher for obese children vs normal weight and overweight children (2.4 vs 0.9 vs 0.8; P = 0.003).
• The average duration of sleep was 8 hours, regardless of weight category.
• Sleep and weight had a nonlinear association.
• Sleep variability was greater on weekends vs weekdays for obese children vs normal-weight and overweight children.
• Total sleep time on weekends was shorter for obese children vs normal-weight and overweight children.
• Normal-weight children had regular sleep duration during the week and tended to have longer sleep duration during weekends.
• Overweight children had a mixed sleep patterns of prolonged sleep as the weekdays progressed to the weekend.
• BMI z scores were linked with overweight children but not with normal-weight or obese children.
• In obese children, there was a positive correlation between sleep variability and triglyceride levels during school days (r = 0.31; P < 0.05).
• Abnormal insulin, low-density lipoprotein and high-sensitivity C-reactive protein levels were more likely to be linked in groups with variable sleep duration or short sleep duration: short sleep on weekdays and normal duration on weekends, long sleep on weekdays and normal duration on weekends and short sleep duration on weekdays and weekends.
• Optimal sleep was represented by the group with long sleep duration on weekdays and weekends.
• Study limitations were actigraphy for only 1 typical school week, lack of visceral and subcutaneous fat measurements, predominantly white subject population and blood measurements in only 36,6% of the participants.

Clinical Implications 

• The average sleep duration for children is 8 hours, regardless of weight.
• Obese children are more likely to have variable and shorter sleep duration on weekends. Altered insulin, low-density lipoprotein  and high-sensitivity C-reactive protein levels are more likely to be linked with variable sleep duration or shorter sleep duration.

Pediatrics. Published online January 24, 2011