The Effect of Cold Exposure on Glucose Tolerance

Inclusion Criteria of healthy population: * Signed informed consent. * White European. * Male. * Age 18 - 40 years at the start of the study. * BMI ≥ 20 and \< 30 kg/m2. Exclusion Criteria of healthy population: * Smoking. * Active diseases (cardiovascular, diabetes mellitus, liver, kidney, cancer or other). * Cold-acclimated (takes daily cold baths, works in a refrigerated environment, or regular cold water swimmer). * Unstable body weight (gain or loss \> 5kg in last 3 months). * Currently undertaking a diet. Inclusion Criteria of prediabetes population: * Signed informed consent. * White European. * Male or female. * Women should be postmenopausal or use hormonal contraceptives. * Age 30 - 75 years at the start of the study. * BMI ≥ 25 and \< 35 kg/m2. * Generally healthy, no medication use that interferes with metabolism. If volunteers need medication (e.g. statin drugs, NSAIDs), it will be reviewed with the dependent physician on an individual basis. * Impaired fasting glucose (5.6 mM to 6.9 mM) and/or blood glucose values 7.8-11.0 mM 2h after glucose drink consumption during OGTT in screening. Exclusion Criteria of prediabetes population: * Smoking. * Active diseases (cardiovascular, diabetes mellitus, liver, kidney, cancer or other). * Cold-acclimated (takes daily cold baths, works in a refrigerated environment, or regular cold water swimmer). * Unstable body weight (gain or loss \> 5kg in last 3 months). * Currently undertaking a diet.