title: Effect of time of day and fasting duration on measures of glycaemia: analysis from the Whitehall II Study.
abstract: OBJECTIVE
  We aimed to study diurnal variation in glucose regulation by examining the effects of time of day and fasting duration on fasting plasma glucose (FPG), 2 h post-load plasma glucose (2hPG) and HbA(1c) levels.
  
  
  METHODS
  We analysed data from 5,978 non-diabetic white men and women from the prospective Whitehall II Study. All studied participants fasted for at least 8 h before a clinical examination, which included an OGTT and anthropometric measurements. We fitted mixed-effects models for FPG, 2hPG and HbA(1c) as outcome variables, and time of day and/or fasting duration as explanatory variables. Models were adjusted for age, BMI and study phase.
  
  
  RESULTS
  Time of day and fasting duration were associated inversely with FPG and positively with 2hPG. The mean difference between measures at 08:00 and 15:00 hours in men/women was -0.46 (95% CI -0.50, -0.42) mmol/l/-0.39 (95% CI -0.46, -0.31) mmol/l and 1.39 (95% CI 1.25, 1.52) mmol/l/1.19 (95% CI 0.96, 1.42) mmol/l for FPG and 2hPG, respectively. HbA(1c) levels were independent of either time. Time of day and fasting duration were independently associated with 2hPG. In contrast, the effect of fasting duration on FPG was markedly attenuated with adjustment for time of day. Ageing, but not obesity, was associated with increased diurnal variation in glucose tolerance.
  
  
  CONCLUSIONS
  Both time of day and fasting duration should be considered in clinical practice and epidemiological studies, since they have clinically relevant effects on FPG and 2hPG levels. As biochemically expected, HbA(1c) levels are independent of time of blood sampling and fasting duration.
authors.affiliation: Department of Medical Physics and Medical Informatics, University of Szeged, Korányi fasor 9, Szeged, Hungary. hulman.adam@med.u-szeged.hu
authors.forename: A
authors.initials: A
authors.lastname: Hulmán
authors.forename: K
authors.initials: K
authors.lastname: Færch
authors.forename: D
authors.initials: D
authors.lastname: Vistisen
authors.forename: J
authors.initials: J
authors.lastname: Karsai
authors.forename: T A
authors.initials: TA
authors.lastname: Nyári
authors.forename: A G
authors.initials: AG
authors.lastname: Tabák
authors.forename: E J
authors.initials: EJ
authors.lastname: Brunner
authors.forename: M
authors.initials: M
authors.lastname: Kivimäki
authors.forename: D R
authors.initials: DR
authors.lastname: Witte
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001786:Blood Glucose / Q000378:metabolism*; D005215:Fasting / Q000097:blood*; D005260:Female; D005951:Glucose Tolerance Test; D006442:Glycated Hemoglobin / Q000378:metabolism; D006801:Humans; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000097:blood; D011446:Prospective Studies; D013997:Time Factors
chemical_list: D001786:Blood Glucose; D006442:Glycated Hemoglobin