Link between short sleep and obesity in humans: a matter of age?

I read with great interest the article by Calvin et al (July 2013 ). 1 The authors found that people whose sleep was restricted to approximately 5 h per night over an 8-day period consumed on average 822 more calories per day than people who slept approximately 7 h per night. 1 This outcome is in-line with previous study fi ndings. For instance, when sleep-deprived for one night, young adults chose greater portion sizes under both fasting and sated conditions than they do after one night of normal sleep. 2 However, in contrast to previous fi ndings, 3 , 4 Calvin et al 1 did not observe any differences in activity energy expenditure or circulating concentrations of leptin and ghrelin. Based on their fi ndings, the authors conclude that short sleep duration, if habitual, may contribute to the high and rising prevalence of obesity in our modern societies. However, one methodologic issue of their study requires a more detailed discussion. Although the sleep groups did not differ in terms of age, their participants’ ages ranged from 18 to 40 years. 1