Vancouver, British Columbia—Tell your patients to turn off the late-night television, get another hour of sleep, and they might just lose some weight or at least slow the bulge, investigators suggested at the annual meeting of the North American Association for the Study of Obesity, The Obesity Society.

"We found that there may be optimal sleeping hours, around 8 hours of sleep per night, where body weight regulation is facilitated," lead investigator Jean-Philippe Chaput, a doctoral candidate in the Division of Kinesiology, Laval University, Quebec, Canada, told IMWR. "Substantial deviations below this level may be associated with increased body weight and adiposity. In addition, sleep variation seems to be associated with variation in leptin levels."

The hormone leptin decreases energy intake and increases energy expenditure, helping to control weight. The inves­tigators looked at whether shorter sleep durations are ­associated with higher body fat measures and lower levels of ­leptin hormone. 

In this retrospective study, investigators analyzed data from 740 adult men (n = 323) and women (n = 417) taken during the decades-long Quebec Family Study. Parti­cipants self-reported average nightly sleep on a sleep questionnaire. Re­searchers in the original study mea­sured patients for body composition and body fat using hydrostatic weighing and indices ­in­clud­ing body mass index, skinfold thickness, and waist circumference. Data on lipid ­profiles and leptin levels were also recorded.

"We found that short sleep duration, 5 to 6 hours as compared to 7 to 8 hours for normal sleepers, predicted an increased risk to be overweight in adults, and short sleep duration was related to a reduced circulating leptin level relative to what is predicted by fat mass," Mr Chaput said.

"Because sleep duration is a potentially modifiable risk factor, these findings may have important clinical implications for the prevention and treatment of obesity," he added.

The retrospective an­alysis indicated that 88% of short-time sleepers had lower levels of leptin than those who sleep longer hours. 

"This suggests that the association between short sleep duration, hormone changes, and obesity is likely to be robust," Shahrad Taheri, MD, PhD, of the University of Bristol, United Kingdom, told IMWR. "This has great public health implications." 

Dr Taheri said that children in particular may be losing sleep by staying up to watch television, surf the Internet, play video or computer games, and send mobile phone text messages. "The association between short sleep duration and obesity occurs in very young children. We know from the longitudinal study of children in Bristol that short sleep duration at such an early age as 30 months is associated with obesity at the age of 7 years. Adolescents are particularly at risk, because their biological clock delays their sleep time, so they go to bed late and wake up early to go to school. This age-group is vulnerable to sleep deprivation."

Mr Chaput cautioned that although these findings are strong, more research is needed before correlations between sleep, leptin, and weight can be asserted ­conclusively. "More direct studies of the changes in leptin levels and their relations to sleep duration are needed. In addition, future studies need to examine the effect of regular and short sleeping hours on appetite, food intake, and obesity. These studies could help answer the ­question of whether the rise in obesity in many societies is partly due to the fact that people are sleeping less," he said.

NAASO, The Obesity Society, reports that Americans now sleep an average of 2 hours less than they did 40 years ago.