Sleep, circadian rhythm, and human body composition – a Mendelian randomization study

The important role of sleep and circadian rhythm in human metabolism has been recognized. Accumulating evidence shows that insufficient sleep, sleep disorders, circadian disruptions, and certain circadian patterns are independent risk factors of metabolic diseases such as obesity and type 2 diabetes. On the other hand, population based studies have highlighted the cross-talks between body composition parameters and metabolic diseases. However, despite that preliminary findings have suggested the associations between sleep variables and body composition, there is a paucity of studies verifying these results. Moreover, recent genome-wide association studies using UK biobank resource have identified genetic loci for sleep duration, insomnia, chronotype, body fat distribution, lean body mass, and bone mineral density. Therefore, a further step investigating the possible causalities between the sleep, circadian rhythm, and body composition by using Mendelian randomization approach may disentangle the unclear associations between these pathophysiological parameters. Findings of this study may provide new evidence linking sleep and circadian patterns/disruptions and body composition outcomes.