LEP and type 2 diabetes mellitus: Sleep restricting healthy young men from 8 h/night to only 4 h/night for 1 week induces insulin resistance to a similar extent as people with type 2 diabetes.33 Sleep shortening also effects hormones that control appetite,34 elevating ghrelin and reducing leptin, which could explain the strong link between sleep deprivation, raised energy intake and weight gain.34 Persistent long sleep and increases in sleep duration over a 5-year period have been linked to higher type 2 diabetes incidence.35 However, the physiological impact of long sleep is yet to be fully understood.