title: Thyrotropin secretion in healthy subjects is robust and independent of age and gender, and only weakly dependent on body mass index.
abstract: BACKGROUND
  Studies of the influence of sex, age, and body weight on TSH secretion are not unanimous. Most reports are based on a single TSH measurement; studies using frequent blood sampling are scarce and include a limited number of selected subjects.
  
  
  OBJECTIVE
  The goal was to investigate TSH dynamics in 117 healthy adults.
  
  
  METHODS
  TSH was measured by a sensitive immunofluorometric assay. Secretion parameters were quantified by automated deconvolution, approximate entropy [ApEn], spikiness, and diurnal properties.
  
  
  RESULTS
  Mean age was 43 years (range, 22-77 y). Mean body mass index (BMI) was 26.8 kg/m(2) (range, 18.3-39.4 kg/m(2)). Daily TSH secretion was 45.4 mU/L (range, 8.0-207 mU/L). There were no sex differences in secretion parameters, including pulse frequency; basal, pulsatile, and total secretion; pulse mode; half life; pulse regularity; ApEn; spikiness; and nycthemeral properties. BMI was positively related to basal secretion. Total secretion correlated negatively with free T₄ (R = 0.225; P = .018). The onset of the nocturnal surge was delayed by increasing BMI and advanced by increasing age. ApEn and spikiness correlated positively with age, especially in men. The 9 am sample correlated strongly with the total 24-hour secretion, explaining two-thirds of the variability.
  
  
  CONCLUSIONS
  This study shows that the 24-hour TSH secretion in healthy volunteers is stable and robust and not influenced by sex, BMI, and age. ApEn in the elderly, especially men, is increased, pointing to a less tight feedback control. Furthermore, aging is associated with advance shifting of the TSH rhythm, which is a phenomenon also observed in other biological rhythms.
authors.affiliation: Department of Endocrinology and Metabolism (F.R., H.P., P.K., N.R.B., A.M.P.), Leiden University Medical Center, 2333 ZA Leiden, The Netherlands; Department of Endocrinology (E.E., E.F.), Amsterdam Medical Center, University of Amsterdam, 1105 AZ Amsterdam, The Netherlands; and Endocrine Research Unit (J.D.V.), Mayo Clinic College of Medicine, Rochester, Minnesota 55905.
authors.forename: Ferdinand
authors.initials: F
authors.lastname: Roelfsema
authors.forename: Hanno
authors.initials: H
authors.lastname: Pijl
authors.forename: Petra
authors.initials: P
authors.lastname: Kok
authors.forename: Erik
authors.initials: E
authors.lastname: Endert
authors.forename: Eric
authors.initials: E
authors.lastname: Fliers
authors.forename: Nienke R
authors.initials: NR
authors.lastname: Biermasz
authors.forename: Alberto M
authors.initials: AM
authors.lastname: Pereira
authors.forename: Johannes D
authors.initials: JD
authors.lastname: Veldhuis
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D000375:Aging / Q000502:physiology; D001823:Body Composition / Q000502:physiology; D015992:Body Mass Index; D002940:Circadian Rhythm / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012727:Sex Characteristics; D012737:Sex Factors; D013972:Thyrotropin / Q000378:metabolism*
chemical_list: D013972:Thyrotropin