Posted on 10 February 2022
Longevity briefs provides a short summary of novel research in biology, medicine, or biotechnology that caught the attention of our researchers in Oxford, due to its potential to improve our health, wellbeing, and longevity.
Why is this research important: Obesity is a serious health problem that affects an increasingly large proportion of the world. According to the World Health Organisation, 1.9 billion adults aged 18 years and older were overweight in 2016, and of those, over 650 million were obese. Previous studies have found that people who get less sleep are more likely to become obese, but is the reverse relationship true? Could getting more sleep aid weight loss?
What did the researchers do: In this study, researchers recruited 80 people aged 21 to 40 years who were overweight (had a body mass index between 25.0 and 29.9) and who habitually slept for less than 6.5 hours a night. They then randomly assigned participants to either receive sleep hygiene counselling aimed at extending their sleep duration to 8.5 hours, or to continue with their habitual sleep pattern.
Over the course of four weeks, researchers calculated participants’ daily energy intake, expenditure, and body energy stores based on a urine based test that involved participants drinking water labelled with naturally occurring isotopes. Participants were still allowed to eat whatever they liked and weren’t asked to track what they were eating.
Key takeaway(s) from this research: In the group that received the intervention, sleep duration increased by 1.2 hours on average compared to the group that received no intervention. The intervention group consumed 270 fewer calories per day on average compared with the control group, and the extent of sleep extension correlated with the size of the reduction in calorie intake (each 1-hour increase in sleep duration was associated with a 162 calorie decrease in daily energy intake). Total energy expenditure did not significantly change in either group.
As for weight, the intervention group lost an average of 0.48kg, while the control group gained an 0.39kg on average.
This study has several strengths: it was a randomised trial design, which is able to support the existence of a causal relationship. Participants were not asked to report their own calorie intake, which eliminates the possibility of self-report bias (in which participants in the intervention group might under-report how much they eat). The trial took place outside of a laboratory setting and participants were left fully in control of their sleep and eating habits, which makes the results more relevant and likely to be applicable to the average person.
The main limitation of this study was arguably its duration. The reduction in calorie intake seen in the intervention group would be expected to result in the loss of around 12kg over the course of 3 years. However, there’s no knowing whether the effects of the sleep extension would last that long. It’s also possible that participants’ daily energy expenditure might have started to decrease if the study had lasted longer (why?), which might have counterbalanced some or all of the decreased calorie intake.
We need longer trials to study this relationship further, and to investigate the mechanisms behind it. Previous studies suggest that reduced sleep can alter the levels of appetite-regulating hormones, and that it can cause changes in brain regions linked to reward-seeking.
Effect of Sleep Extension on Objectively Assessed Energy Intake Among Adults With Overweight in Real-life Settings: http://jamanetwork.com/article.aspx?doi=10.1001/jamainternmed.2021.8098