title: The role of obesity, different fat compartments and sleep apnea severity in circulating leptin levels: the Icelandic Sleep Apnea Cohort study.
abstract: OBJECTIVE
  To assess whether sleep apnea severity has an independent relationship with leptin levels in blood after adjusting for different measures of obesity and whether the relationship between obstructive sleep apnea (OSA) severity and leptin levels differs depending on obesity level.
  
  
  METHODS
  Cross-sectional study of 452 untreated OSA patients (377 males and 75 females), in the Icelandic Sleep Apnea Cohort (ISAC), age 54.3±10.6 (mean±s.d.), body mass index (BMI) 32.7±5.3 kg m(-2) and apnea-hypopnea index 40.2±16.1 events per h. A sleep study and magnetic resonance imaging of abdominal visceral and subcutaneous fat volume were performed, as well as fasting serum morning leptin levels were measured.
  
  
  RESULTS
  Leptin levels were more highly correlated with BMI, total abdominal and subcutaneous fat volume than visceral fat volume per se. No relationship was found between sleep apnea severity and leptin levels, assessed within three BMI groups (BMI <30, BMI 30-35 and BMI > or =35 kg m(-2)). In a multiple linear regression model, adjusted for gender, BMI explained 38.7% of the variance in leptin levels, gender explained 21.2% but OSA severity did not have a significant role and no interaction was found between OSA severity and BMI on leptin levels. However, hypertension had a significant effect on the interaction between OSA severity and obesity (P=0.04). In post-hoc analysis for nonhypertensive OSA subjects (n=249), the association between leptin levels and OSA severity explained a minor but significant variance (3.2%) in leptin levels. This relationship was greatest for nonobese nonhypertensive subjects (significant interaction with obesity level). No relationship of OSA severity and leptin levels was found for hypertensive subjects (n=199).
  
  
  CONCLUSIONS
  Obesity and gender are the dominant determinants of leptin levels. OSA severity is not related to leptin levels except to a minor degree in nonhypertensive nonobese OSA subjects.
authors.affiliation: Department of Respiratory Medicine and Sleep, Landspitali-The National University Hospital of Iceland, Reykjavik, Iceland. ernasif@landspitali.is
authors.forename: E S
authors.initials: ES
authors.lastname: Arnardottir
authors.forename: G
authors.initials: G
authors.lastname: Maislin
authors.forename: N
authors.initials: N
authors.lastname: Jackson
authors.forename: R J
authors.initials: RJ
authors.lastname: Schwab
authors.forename: B
authors.initials: B
authors.lastname: Benediktsdottir
authors.forename: K
authors.initials: K
authors.lastname: Teff
authors.forename: S
authors.initials: S
authors.lastname: Juliusson
authors.forename: A I
authors.initials: AI
authors.lastname: Pack
authors.forename: T
authors.initials: T
authors.lastname: Gislason
mesh_terms: D000328:Adult; D015415:Biomarkers / Q000097:blood; D001823:Body Composition; D015992:Body Mass Index; D015331:Cohort Studies; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D006973:Hypertension / Q000097:blood* / Q000453:epidemiology / Q000503:physiopathology; D007055:Iceland / Q000453:epidemiology; D050152:Intra-Abdominal Fat / Q000473:pathology*; D020738:Leptin / Q000097:blood*; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000097:blood* / Q000150:complications / Q000453:epidemiology / Q000503:physiopathology; D017286:Polysomnography; D012720:Severity of Illness Index; D017678:Sex Distribution; D012891:Sleep Apnea Syndromes / Q000097:blood* / Q000453:epidemiology / Q000209:etiology / Q000503:physiopathology; D050151:Subcutaneous Fat / Q000473:pathology*; D011795:Surveys and Questionnaires; D013997:Time Factors
chemical_list: D015415:Biomarkers; D020738:Leptin