Circadian Rhythmicity in Cold-induced Thermogenesis

The Impact of Circadian Rhythmicity in Cold-induced Thermogenesis in Lean and Obese Subjects

This study aims to investigate whether maximum cold-induced non-shivering thermogenesis (e.g. thermogenesis as a consequence of BAT activity) differs between morning and evening.

Brown adipose tissue (BAT) recently emerged as a novel player in energy expenditure (EE) in humans as it combusts fatty acids and glucose towards heat. Human BAT can be activated by sympathetic stimulation resulting from cold exposure or treatment with sympathomimetic drugs. Short-term acclimation to mild cold was shown to reduce fat mass in obese subjects and decrease peripheral insulin resistance of patients with T2DM. Recently, in preclinical studies the investigators showed that BAT has a circadian rhythm. It is currently unknown whether this is also the case in humans. The investigators postulate that BAT activity should display a circadian rhythm that adapts to changes in circadian behavior, and may determine glucose/lipid levels throughout the day.

Inclusion Criteria:

• Dutch white Caucasian males or females
• Age: 18-35 years
• Lean group: BMI ≥ 18 and ≤ 25 kg/m2
• Obese glucose tolerant group: BMI ≥ 30 and ≤ 42 kg/m2 and fasted plasma glucose levels < 5.5 and/or 2 h after OGTT ≤ 7.8 mM
• Obese impaired glucose tolerant group: BMI ≥ 30 and ≤ 42 kg/m2 and fasted plasma glucose levels ≥ 5.5 and/or 2 h after OGTT between 7.8 and 11.1 mM

Exclusion Criteria:

• Diabetes mellitus (determined on basis of fasting or OGTT defined by ADA criteria (30)
• Any other active endocrine disease (thyroid disease, any signs of Cushing's syndrome, adrenal disease and lipid-associated disorders such as familial hypercholesterolemia)
• Any chronic renal or hepatic disease
• Use of medication known to influence glucose and/or lipid metabolism or brown fat activity (e.g. beta blockers, antidepressants)
• Smoking
• Abuse of alcohol or other substances
• Pregnancy
• Participation in an intensive weight-loss program or vigorous exercise program during the last year before the start of the study
• Current participation in another research projects that may influence the current research project
• Clinically relevant abnormalities in clinical chemistry at screening (to be judged by the study physician)