Shorter sleep is associated with increases in body mass index (BMI) in adolescents aged 14 to 18 years, especially in heavier adolescents, according to a new study. Those who sleep an extra hour or more a night could lower their BMI and thereby prevent overweight and obesity.
“Physical inactivity and increased caloric intake may explain why we observed an association between short sleep and adolescent obesity,” lead author Jonathan A. Mitchell, PhD, postdoctoral fellow in the Center for Clinical Epidemiology and Biostatistics at Penn Medicine in Philadelphia, told ConsultantLive.
“Short sleepers could be more tired during the daytime and spend less time being physically active as a consequence,” Dr Mitchell said. “It is also possible that short sleep increases total caloric intake due to more eating opportunities.”
In addition, studies have found that short sleep can affect hormones that regulate appetite and energy homeostasis, Dr Mitchell noted. “Such hormonal changes could also explain why we observed an association between short sleep and adolescent obesity.”
Dr Mitchell and colleagues recruited 1390 adolescents from suburban high schools in Philadelphia when they entered ninth grade and monitored them every 6 months through 12th grade. The researchers calculated individual BMIs. Students self-reported their sleep times.
Each additional hour of sleep was associated with only a slight reduction in BMI (0.07 kg/m2) at the 10th BMI percentile. In comparison, greater reductions in BMI were observed at the 50th and 90th percentiles (0.17 kg/m2 and 0.28 kg/m2, respectively).
Increasing sleep from 8 to 10 hours per day at age 18 years could result in a 4% reduction in the number of adolescents with a BMI higher than 25 kg/m2, Dr Mitchell noted.
The relationship between disrupted circadian rhythms and weight gain has been well-documented in animal models. “Mice that have had a circadian clock gene knocked out gain more weight compared to wild types and tend to eat more frequently during their light cycle (equivalent to eating at night in diurnal humans),” said Dr Mitchell. “It is not known if these findings in mice translate to humans, and more research is needed to determine if staying awake at night and eating at night associates with adolescent obesity.”
Primary care physicians should advise adolescent patients to adopt good sleep hygiene practices, such as establish routine bed and wake times each day, associate the bedroom with sleep and not television viewing, and increase physical activity during the daytime, Dr Mitchell suggested.
“Primary care physicians and other health care professionals could also lend their support to changes in policies that would help promote longer sleep duration among adolescents, for example, later high school start times and more physical education classes to increase daytime physical activity,” he said.
“Attaining sufficient sleep needs to receive greater attention as we try and address the high level of childhood obesity,” Dr Mitchell added. “Initiatives to date, such as Let’s Move!, focus on healthier eating and being more physically active, but they do not recognize the importance of sufficient sleep duration.”
The researchers reported their results online on April 8 in Pediatrics.