title: Diurnal changes of biochemical metabolic markers in healthy young males - the Bispebjerg study of diurnal variations.
abstract: BACKGROUND
  To examine whether time of the day has an effect on the circulating levels of metabolism parameters.
  
  
  METHODS
  Venous blood samples were obtained under standardized conditions from 24 healthy young men every third hour through 24 hours. The metabolic markers and melatonin were examined at each time-point and data were analyzed by rhythmometric statistical methods.
  
  
  RESULTS
  The normal 24-h rhythms of the participants were confirmed by significant oscillation of melatonin (p < 0.0001). Cosinor analysis revealed significant diurnal 24-h rhythms of five of the seven examined markers: Total cholesterol (p = 0.01, amplitude (amp) = 0.18 mmol/L) peaking in the early afternoon, Glucose (p < 0.0001, amp = 0.35 mmol/L) peaking around midnight, C-peptide (p < 0.001, amp = 360 pmol/L), triglyceride (p < 0.0001, amp = 0.37 mmol/L) peaking in the afternoon and low-density lipoprotein cholesterol (p = 0.003, amp = 0.16 mmol/L) peaking in the morning. C-peptide, triglyceride, and glucose had the highest 24-h oscillations in proportion to the reference ranges of the parameters for healthy young men. Glycated haemoglobin (HbA1c) (p = 0.07, amp = 0.57 mmol/L) and high-density lipoprotein (p = 0.09, amp = 0.06 mmol/L) did not show significant oscillations.
  
  
  CONCLUSIONS
  When diagnosing and monitoring metabolic disorders compensation for the 24-h variation of the biochemical metabolic markers is needed especially C-peptide, triglyceride and glucose. Furthermore, the stable HbA1c level through 24 h makes it an accurate diagnostic test for diabetes mellitus.
authors.affiliation: a Department of Clinical Biochemistry , Faculty of Health Science, Bispebjerg Hospital, University of Copenhagen , Copenhagen , Denmark.|b Department of Clinical Biochemistry , Faculty of Health Science, Rigshospitalet - Glostrup, University of Copenhagen , Copenhagen , Denmark.
authors.forename: Henriette P
authors.initials: HP
authors.lastname: Sennels
authors.affiliation: a Department of Clinical Biochemistry , Faculty of Health Science, Bispebjerg Hospital, University of Copenhagen , Copenhagen , Denmark.
authors.forename: Henrik L
authors.initials: HL
authors.lastname: Jørgensen
authors.affiliation: a Department of Clinical Biochemistry , Faculty of Health Science, Bispebjerg Hospital, University of Copenhagen , Copenhagen , Denmark.
authors.forename: Jan
authors.initials: J
authors.lastname: Fahrenkrug
mesh_terms: D000328:Adult; D015415:Biomarkers / Q000097:blood; D050260:Carbohydrate Metabolism; D002940:Circadian Rhythm; D006442:Glycated Hemoglobin / Q000378:metabolism; D064368:Healthy Volunteers; D006801:Humans; D050356:Lipid Metabolism; D008297:Male; D008550:Melatonin / Q000097:blood*; D012016:Reference Values; D055815:Young Adult
chemical_list: D015415:Biomarkers; D006442:Glycated Hemoglobin; D008550:Melatonin; C517652:hemoglobin A1c protein, human
keywords: Biological clocks; chronobiology disorders; circadian clocks; circadian rhythm; diabetes mellitus; lipids; metabolic syndrome X