title: Are serum thyrotropin levels within the reference range associated with endothelial function?
abstract: OBJECTIVE
  High serum thyrotropin (TSH) levels within the reference range might be associated with an increased cardiovascular risk. In the present study, we investigated the association between serum TSH levels and flow-mediated dilation (FMD) as a measure of endothelial dysfunction.
  
  
  RESULTS
  The study population comprised 1364 subjects (670 women) aged 25-85 years with serum TSH levels between 0.25 and 2.12 mIU/L recruited from 5-year follow-up of the Study of Health in Pomerania. No interventions were performed. Measurements of FMD and nitrate-mediated dilation (NMD) were performed in the supine position using standardized ultrasound techniques. FMD and NMD values below the median of each distribution were considered decreased. Analyses adjusted for age, sex, smoking, and systolic and diastolic blood pressure revealed a non-significant inverse trend between serum TSH levels and FMD (P = 0.130). Subjects with serum TSH levels above the highest quartile had lower median FMD values relative to subjects with serum TSH levels below the lowest quartile (4.86 vs. 5.43%, P < 0.05). A linear inverse trend between serum TSH levels and decreased FMD barely missed statistical significance (P = 0.138). Subjects with high serum TSH levels had higher odds of decreased FMD relative to subjects with low serum TSH levels (odds ratio 1.42; 95% confidence interval 1.02; 1.96; P < 0.05). These associations were more pronounced in men than in women. There were no such associations for NMD.
  
  
  CONCLUSIONS
  Serum TSH levels within the upper reference range are associated with impaired endothelial function. Our findings contribute to the discussion on whether the upper TSH reference limit should be redefined.
authors.affiliation: Institut für Community Medicine, Ernst-Moritz-Arndt-Universität, Walther Rathenau Str. 48, D-17487 Greifswald, Germany.
authors.forename: Henry
authors.initials: H
authors.lastname: Völzke
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Robinson
authors.forename: Thomas
authors.initials: T
authors.lastname: Spielhagen
authors.forename: Matthias
authors.initials: M
authors.lastname: Nauck
authors.forename: Anne
authors.initials: A
authors.lastname: Obst
authors.forename: Ralf
authors.initials: R
authors.lastname: Ewert
authors.forename: Birger
authors.initials: B
authors.lastname: Wolff
authors.forename: Henri
authors.initials: H
authors.lastname: Wallaschofski
authors.forename: Stephan B
authors.initials: SB
authors.lastname: Felix
authors.forename: Marcus
authors.initials: M
authors.lastname: Dörr
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015415:Biomarkers / Q000097:blood; D002318:Cardiovascular Diseases / Q000097:blood* / Q000209:etiology / Q000503:physiopathology; D004730:Endothelium, Vascular / Q000000981:diagnostic imaging / Q000503:physiopathology*; D004812:Epidemiologic Methods; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012016:Reference Values; D013972:Thyrotropin / Q000097:blood*; D014463:Ultrasonography; D014664:Vasodilation / Q000502:physiology*
chemical_list: D015415:Biomarkers; D013972:Thyrotropin