title: Circulating irisin in healthy, young individuals: day-night rhythm, effects of food intake and exercise, and associations with gender, physical activity, diet, and body composition.
abstract: BACKGROUND
  The myokine irisin may increase energy expenditure and affect metabolism.
  
  
  OBJECTIVE
  The objective of the study was to elucidate predictors of irisin and study whether circulating irisin may have day-night rhythm in humans.
  
  
  METHODS
  This was an observational, cross-sectional study with an additional 24-hour prospective observational arm (day-night rhythm substudy) and two prospective interventional arms (mixed meal substudy and exercise substudy).
  
  
  METHODS
  The study was conducted at the Hellenic Military School of Medicine (Thessaloniki, Greece).
  
  
  METHODS
  One hundred twenty-two healthy, young individuals were subjected to anthropometric and body composition measurements, and their eating and exercise behavior profiles were assessed with validated questionnaires. Subgroups were subjected to day-night rhythm, standardized meal ingestion, and 30-minute aerobic exercise studies.
  
  
  METHODS
  Circulating irisin levels were measured.
  
  
  RESULTS
  Ιrisin levels were lower in males than females (P = .02) after adjustment for lean body mass, which was its major determinant. Irisin levels followed a day-night rhythm (P < .001) with peak at 9:00 pm. Irisin levels were increased at the end of exercise (84.1 ± 10.0 vs 105.8 ± 14.3 ng/mL; P < .001). Irisin levels were not affected by intake of a standardized meal and were not associated with caloric intake or diet quality.
  
  
  CONCLUSIONS
  In healthy, young individuals, circulating irisin displays a day-night rhythm, is correlated with lean body mass, and increases acutely after exercise.
authors.affiliation: Department of Endocrinology (A.D.A., S.D.), 424 General Military Hospital, 56429 Thessaloniki, Greece; Second Medical Clinic (S.A.P.), Department of Medicine, Aristotle University of Thessaloniki, Ippokration General Hospital, 54642 Thessaloniki, Greece; Hellenic Military School of Medicine (Z.G.S., G.K., E.C.S., D.M.), 54638 Thessaloniki, Greece; Department of Nutrition-Dietetics (M.F.V., A.A., T.K.-L.), Alexander Technological Education Institute of Thessaloniki, Thessaloniki, Greece; School of Physical Education and Sports Science (A.S., V.M.) and Medical School (P.C.), Aristotle University of Thessaloniki, 54636 Thessaloniki, Greece; and Division of Endocrinology, Diabetes, and Metabolism (G.P., A.F., C.S.M.), Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts 02115.
authors.forename: Athanasios D
authors.initials: AD
authors.lastname: Anastasilakis
authors.forename: Stergios A
authors.initials: SA
authors.lastname: Polyzos
authors.forename: Zacharias G
authors.initials: ZG
authors.lastname: Saridakis
authors.forename: Georgios
authors.initials: G
authors.lastname: Kynigopoulos
authors.forename: Elpida C
authors.initials: EC
authors.lastname: Skouvaklidou
authors.forename: Dimitrios
authors.initials: D
authors.lastname: Molyvas
authors.forename: Maria F
authors.initials: MF
authors.lastname: Vasiloglou
authors.forename: Aggeliki
authors.initials: A
authors.lastname: Apostolou
authors.forename: Thomai
authors.initials: T
authors.lastname: Karagiozoglou-Lampoudi
authors.forename: Aikaterina
authors.initials: A
authors.lastname: Siopi
authors.forename: Vassilis
authors.initials: V
authors.lastname: Mougios
authors.forename: Panagiotis
authors.initials: P
authors.lastname: Chatzistavridis
authors.forename: Grigorios
authors.initials: G
authors.lastname: Panagiotou
authors.forename: Andreas
authors.initials: A
authors.lastname: Filippaios
authors.forename: Sideris
authors.initials: S
authors.lastname: Delaroudis
authors.forename: Christos S
authors.initials: CS
authors.lastname: Mantzoros
mesh_terms: D052242:Adiponectin / Q000097:blood; D001823:Body Composition / Q000502:physiology*; D015992:Body Mass Index; D002940:Circadian Rhythm / Q000502:physiology*; D003430:Cross-Sectional Studies; D004435:Eating / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D005247:Feeding Behavior; D005260:Female; D005353:Fibronectins / Q000097:blood*; D064368:Healthy Volunteers; D006801:Humans; D020738:Leptin / Q000097:blood; D008297:Male; D009043:Motor Activity / Q000502:physiology*; D011446:Prospective Studies; D012737:Sex Factors; D011795:Surveys and Questionnaires; D055815:Young Adult
chemical_list: C499918:ADIPOQ protein, human; D052242:Adiponectin; C577593:FNDC5 protein, human; D005353:Fibronectins; D020738:Leptin