Children Who Sleep Less Are More Likely to Be Overweight

Laurie Barclay, MD

May 31, 2011 — Young children who do not get enough sleep are at increased risk of becoming overweight, according to the results of a longitudinal study reported online May 26 in the BMJ.

"Despite recent data suggesting that the dramatic increases in overweight and obesity in children and adolescents seen over the past three decades have begun to plateau, rates remain alarmingly high," write Philippa J. Carter, from the Department of Women's and Children's Health, University of Otago, Dunedin, New Zealand, and colleagues from the Family Lifestyle, Activity, Movement and Eating (FLAME) study. "Concurrent with these increases has been a reduction in how long children sleep, raising the question of a link. Several recent reviews have now shown a relatively consistent relation between shorter sleep duration and increased risk of overweight in childhood, particularly in younger children."

The goal of the study was to examine whether reduced sleep duration in young children is associated with differences in body composition and the risk of becoming overweight, defined as a body mass index (BMI) in the 85th centile or more. The study sample consisted of 244 children recruited from a birth cohort in Dunedin, New Zealand, and observed from ages 3 to 7 years with repeated annual measurements including dual-energy x-ray absorptiometry.

Bioelectrical impedance was used to measure BMI, fat mass (kg), and fat-free mass (kg), and accelerometry was used to measure physical activity and sleep duration. A questionnaire examined dietary intake of fruit and vegetables and noncore foods; television viewing; and family factors, including maternal BMI and education, birth weight, and smoking during pregnancy.

Each additional hour of sleep at ages 3 to 5 years was associated with a decrease in BMI of 0.48 (95% confidence interval [CI], 0.01 - 0.96) and a 0.39 lower risk of being overweight (95% CI, 0.24 - 0.63) at age 7 years, after adjustment for multiple confounding variables. These associations were strengthened by further adjustment for BMI at age 3 years.

The observed differences in BMI were explained by differences in fat mass index (−0.43; 95% CI, −0.82 to −0.03) more so than by differences in fat-free mass index (−0.21; 95% CI, −0.41 to −0.00), suggesting negative effects on body composition.

"Young children who do not get enough sleep are at increased risk of becoming overweight, even after adjustment for initial weight status and multiple confounding factors," the study authors write. "This weight gain is a result of increased fat deposition in both sexes rather than additional accumulation of fat free mass."

Limitations of this study include relatively small sample size and placement of the accelerometers at only 1 site.

In an accompanying editorial, Francesco P. Cappuccio and Michelle A. Miller, from the University of Warwick, Warwick, United Kingdom, suggest that prolonged lack of sleep in children may negatively affect long-term health in ways other than directly contributing to overweight and obesity.

"The ultimate proof of principle should come from a randomised trial of sleep 'prolongation' on weight change," Drs. Cappuccio and Miller write. "The problem is that currently we do not have an effective and reproducible intervention tool. Future research should therefore explore and validate new behavioural (non-drug based) methods to prolong childrens' and adults' sleeping time. In the meantime it would do no harm to advise people that a sustained curtailment of sleeping time might contribute to long term ill health in adults and children."

The University of Otago, the Child Health Research Foundation, the New Zealand Heart Foundation, and the Dean's Bequest-AAW Jones Trust supported this study. The study authors and editorialists have disclosed no relevant financial relationships.

BMJ. 2011;342:d2712, d3306. Full text Editorial Extract