GHRL and metabolic syndrome: Sleep disorders or short sleep duration can cause hypertension, overweight, obesity, type 2 diabetes, and dyslipidemia through affect sympathetic nerve activity [9], regulate leptin and ghrelin [10, 11], reduce insulin sensitivity, promote insulin resistance [12, 13], stimulate lipodieresis, increase plasma free fatty acid level [14]and other multiple biological mechanisms, all of which are risk factors for MetS.