MTNR1B and diabetes mellitus: The interplay between melatonin and human glucose metabolism has recently gained a lot of interest [29] due to evidence for adverse effects of circadian misalignment (e.g. night-shift work) on glucose metabolism [26, 30] and the discovery of type 2 diabetes mellitus risk variants in the melatonin receptor 1B gene, i.e. MTNR1B [31, 32].