| Outcome Measures: |
Primary: Change of insulin sensitivity, Insulin sensitivity is assessed by a hyperinsulinemic euglycemic clamp, unit: mg/kg/min (mg of glucose to maintain euglycemia per kilogram of weight per minuts), The outcome will be measured after 3 months of placebo treatment and after 3 months of melatonin treatment and compared afterwards with a paired T-tes|Change of insulin secretion change, Insulin secretion is assessed by an intravenous glucose tolerance test, unit: pmol/L (insulin), The outcome will be measured after 3 months of placebo treatment and after 3 months of melatonin treatment|MTNR1a rs10830963 influence on change in insulin sensitivity and insulin secretion, MTNR1a rs10830963 genotype influence on insulin sensitivity and insulin secretion (see outcome 1 + 2), The outcome will be measured after 3 months of placebo treatment and again after 3 months of melatonin treatment|Change of insulin signalling, Insulin signalling in muscle and adipose tissue assessed by western blot, The outcome will be measured after 3 months of placebo treatment and after 3 months of melatonin treatment | Secondary: Change of ambulatory blood pressure, Ambulatory blood pressure assessed with Mobil-O-graph, I.E.M., Stolberg, Germany (Unit: mmHg), The outcome will be measured after 3 months of placebo treatment and after 3 months of melatonin treatment|Change of arterial stiffness, Arterial stiffness assessed with Mobil-O-graph, I.E.M., Stolberg, Germany (unit: m/s), The outcome will be measured after 3 months of placebo treatment and after 3 months of melatonin treatment|Change of gut microbiome, Feces analysis of microbial mRNA, The outcome will be measured after 3 months of placebo treatment and after 3 months of melatonin treatment|Change of sleep evaluation 1, Pittsburg Sleep Quality Index Questionnaire (Points on a scale: range 0-57), The outcome will be measured after 3 months of placebo treatment and after 3 months of melatonin treatment|Change of sleep evaluation 2, Epworth Sleepiness Scale Questionnaire (Points on a scale: range 0-24), After 3 months treatmentThe outcome will be measured after 3 months of placebo treatment and after 3 months of melatonin treatment|Change of psychological health 1, Major Depression Inventory Questionnaires (points on a scale: range 0-65), The outcome will be measured after 3 months of placebo treatment and after 3 months of melatonin treatment|Change of psychological health 2, World Health Organization 5 Questionnaires (points on a scale: range 0-25), The outcome will be measured after 3 months of placebo treatment and after 3 months of melatonin treatment|Hormonal changes, Ghrelin, HbA1c, GLP-1, GLP-2, GIP, free fatty acids (FFA), leptin, cytokines, adiponectin, growth hormone, cortisol, hsCRP, CD163, MBL, IGF-1 and proinsulin measured by ELISA, RIA, or routine biochemical analysis. Unit: pmol/L, The outcome will be measured after 3 months of placebo treatment and after 3 months of melatonin treatment|Change of glucose and palmitate kinetics, Tracer technique with infusion of radioactive labeled glucose and palmitate for determination of rate of appereance. Unit: mikromol/min, The outcome will be measured after 3 months of placebo treatment and after 3 months of melatonin treatment|Change of regional glucose and palmitate uptake, Forearm model with arteriovenous differences of glucose and palmitate (Arterial glucose minus venous glucose = forearm uptake (unit mmol/l). The same applies for palmitate, The outcome will be measured after 3 months of placebo treatment and after 3 months of melatonin treatment|Change of DEXA-scans, Evaluation of body composition and bone mineral density by DEXA-scan, The outcome will be measured after 3 months of placebo treatment and after 3 months of melatonin treatment|Change of assessment of respiratory quotient (RQ), Assessment of respiratory quotient (RQ) with indirect calorimetry (unit: VCO2/VO2), The outcome will be measured after 3 months of placebo treatment and after 3 months of melatonin treatment|Change of assessment of resting energy expenditure (REE), Assessment of resting energy expenditure (REE) with indirect calorimetry (Unit J/s), The outcome will be measured after 3 months of placebo treatment and after 3 months of melatonin treatment
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