title: Frequent extreme cold exposure and brown fat and cold-induced thermogenesis: a study in a monozygotic twin.
abstract: BACKGROUND
  Mild cold acclimation is known to increase brown adipose tissue (BAT) activity and cold-induced thermogenesis (CIT) in humans. We here tested the effect of a lifestyle with frequent exposure to extreme cold on BAT and CIT in a Dutch man known as 'the Iceman', who has multiple world records in withstanding extreme cold challenges. Furthermore, his monozygotic twin brother who has a 'normal' sedentary lifestyle without extreme cold exposures was measured.
  
  
  METHODS
  The Iceman (subject A) and his brother (subject B) were studied during mild cold (13°C) and thermoneutral conditions (31°C). Measurements included BAT activity and respiratory muscle activity by [18F]FDG-PET/CT imaging and energy expenditure through indirect calorimetry. In addition, body temperatures, cardiovascular parameters, skin perfusion, and thermal sensation and comfort were measured. Finally, we determined polymorphisms for uncoupling protein-1 and β3-adrenergic receptor.
  
  
  RESULTS
  Subjects had comparable BAT activity (A: 1144 SUVtotal and B: 1325 SUVtotal), within the range previously observed in young adult men. They were genotyped with the polymorphism for uncoupling protein-1 (G/G). CIT was relatively high (A: 40.1% and B: 41.9%), but unlike during our previous cold exposure tests in young adult men, here both subjects practiced a g-Tummo like breathing technique, which involves vigorous respiratory muscle activity. This was confirmed by high [18F]FDG-uptake in respiratory muscle.
  
  
  CONCLUSIONS
  No significant differences were found between the two subjects, indicating that a lifestyle with frequent exposures to extreme cold does not seem to affect BAT activity and CIT. In both subjects, BAT was not higher compared to earlier observations, whereas CIT was very high, suggesting that g-Tummo like breathing during cold exposure may cause additional heat production by vigorous isometric respiratory muscle contraction. The results must be interpreted with caution given the low subject number and the fact that both participants practised the g-Tummo like breathing technique.
authors.affiliation: Department of Human Biology, School for Nutrition, Toxicology and Metabolism - NUTRIM, Maastricht, the Netherlands.
authors.forename: Maarten J
authors.initials: MJ
authors.lastname: Vosselman
authors.affiliation: Department of Surgery (G.V.), Erasmus Medical Center, Rotterdam, the Netherlands.
authors.forename: Guy H E J
authors.initials: GH
authors.lastname: Vijgen
authors.affiliation: Department of Human Biology, School for Nutrition, Toxicology and Metabolism - NUTRIM, Maastricht, the Netherlands.
authors.forename: Boris R M
authors.initials: BR
authors.lastname: Kingma
authors.affiliation: Department of Nuclear Medicine, Maastricht University Medical Center+, Maastricht, the Netherlands.
authors.forename: Boudewijn
authors.initials: B
authors.lastname: Brans
authors.affiliation: Department of Human Biology, School for Nutrition, Toxicology and Metabolism - NUTRIM, Maastricht, the Netherlands.
authors.forename: Wouter D
authors.initials: WD
authors.lastname: van Marken Lichtenbelt
mesh_terms: D002001:Adipose Tissue, Brown / Q000378:metabolism*; D003080:Cold Temperature; D055873:Extreme Cold; D019788:Fluorodeoxyglucose F18; D006801:Humans; D008297:Male; D008875:Middle Aged; D049268:Positron-Emission Tomography; D022722:Thermogenesis / Q000502:physiology*; D014430:Twins, Monozygotic
chemical_list: D019788:Fluorodeoxyglucose F18