Jury still out on obesity-sleep link

THE role of adequate sleep in weight reduction remains controversial, says an Australian sleep physician, after Canadian researchers suggested that sleep habits be addressed in weight management advice.

In a commentary in the CMAJ last week, researchers from the Healthy Active Living and Obesity Research Group at the Children’s Hospital of Eastern Ontario Research Institute, Canada, wrote that there was an accumulating body of evidence suggesting that “sleeping habits should not be overlooked when prescribing a weight-reduction program to a patient with obesity”. (1)

“Sleep should be included as part of the lifestyle package that traditionally has focused on diet and physical activity,” they wrote.

However, Professor Ron Grunstein, professor of sleep medicine and head of the NHMRC Centre for Integrated Research and Understanding of Sleep, said care needed to be taken not to “create insomnia” by advising people to have a standard amount of sleep.

“It’s good health advice to get adequate sleep and one of the benefits may well be that you are less likely to eat the wrong sort of food”, he said, but added that there has yet to be a convincing, randomised trial to prove the link.

“I don’t think you should create insomnia by saying that everyone needs 8 hours’ sleep to function normally, but I think it’s reasonable to say that the vast majority of people should aim at more than 6 hours’ sleep”, said Professor Grunstein, who is also a staff specialist physician in respiratory and sleep medicine at Royal Prince Alfred Hospital, Sydney.

He said many people underreported the amount of sleep they’d had and there were complexities in how the brain perceived sleep.

“It’s possible for parts of the brain to be more asleep than others”, he said. “As we have understood the brain a lot more and there’s better ways to image the brain, you realise sleep is not always equal across the brain.”

In the CMAJ commentary, the researchers reported that studies had provided evidence that insufficient sleep enhanced hedonic stimulus processing in the brain underlying the drive to consume food, and increased concentrations of hormones, such as ghrelin and cortisol, which affected appetite control.

Professor Grunstein said a hormonal link was possible as some studies, in controlled environments over short periods of time, had shown that hormones related to hunger and preference for fatty foods tended to increase with shorter sleep duration.

However, he said there could also be practical reasons for an association between sleep quantity and weight. “If people feel tired and sleepy, they’re less likely to exercise and use up energy”, he said.

Professor Jennifer O’Dea, professor of health education and nutrition education at the University of Sydney, said the Canadian commentary showed the importance of a holistic approach to health, with adequate sleep being a crucial factor.

Professor O’Dea said the link between sleep and obesity was “pretty solidified” in her mind with the publication of research, of which she was lead author, earlier this year in Pediatric Obesity. (2)

The 4-year, longitudinal study of more than 900 Australian schoolchildren found that consistent low sleep and low socioeconomic status was associated with higher body mass index, and the trend became stronger as children entered adolescence.

“People are sacrificing sleep for other things, but the research is showing that you can’t sacrifice sleep for work, you can’t sacrifice it for physical activity”, Professor O’Dea told MJA Insight. “You have to strike that balance and I think ... people are going to have to be taught how to strike that balance.”

Professor Grunstein said the possible link between sleep and weight was worth further investigation. “If you can show convincingly that lack of sleep or short sleep hours contributes to weight gain ... then I think that’s important.”

- Nicole Mackee

1. CMAJ 2012; Online 18 September
2. Pediatric Obesity 2012; 7: 295-303

Posted 24 September 2012