Nicotinamide Adenine Dinucleotide (NAD+) Metabolism in Human Brown Adipose Tissue

Inclusion Criteria: * Willingness to provide informed consent to participate in the BATNAD study * Must be able to read and speak English/Finnish/Swedish well enough to completely understand the instructions and provide informed consent * Age 30-55 (sedentary lifestyle) * BMI = 18-25 kg/m2 (normal-weight subjects) * BMI ≥ 28 kg/m2 and waist circumference more than 100 cm in men and more than 90 cm in women (subjects with obesity) Exclusion Criteria: * Inability to have PET/CT (claustrophobia, metal implants, recent tattoo including metal components, weight \> 200 kg) * Pregnancy and pregnancy related conditions (postpartum/lactation during the last 12 months, or planning to become pregnant soon) * Major alterations in the menstrual cycle (e.g., amenorrhea) * Use of nicotine based products * Hypo- or hyper- thyroidism (medical history, TSH, T3 or T4 levels out of the normal range) * Diabetes mellitus (fasting Hb1Ac \>6.5% or fasting glycaemia\> 7.0 mmol/) * Abnormal oral glucose tolerance test (2h OGTT \> 11.1 mmol/L) * Hypertension (blood pressure \> 160/100 mmHg) * Abnormal cardiovascular status (arrhythmia and/or long QTc in ECG, abnormal cardiac murmur, previous history of cardiovascular disease) * Abnormal coagulopathy (e.g., clotting abnormality) * Malignancies * Immunological, autoimmune and primary/secondary immunodeficiency disorders (including or not any active treatment) * Virus or bacterial infection (both asymptomatic and symptomatic picture) within the 45 days prior to the study start * Vaccination within the 45 days prior to the study start * Episode of fever or major surgery, burns and traumas within the month prior to the study start * Chronic infections requiring chronic antibiotic or anti-viral treatment * Whole blood donation in the last 3 months (\>400 mL of blood) or plans for blood donation during the entire protocol period * Weight change (intentional or not) over the last 6-months more than 5% of body weight, or plan to lose weight during the study * Allergy to lidocaine or epinephrine, or other local anaesthetics * Previous participation to studies where PET or CT method is used * Use of any medication that, in the opinion of local clinician/researcher, would negatively impact or mitigate full participation and completion, or could influence the study results. This especially applies to the use of β or α adrenergic receptors agonists/antagonists (e.g., β-blockers). * Any other cardiovascular, pulmonary, orthopaedic, neurologic, psychiatric or other conditions that, in the opinion of the local clinician/researcher, would preclude participation and successful completion of the protocol, or that would negatively impact or mitigate participation in and completion of the protocol