title: Day-to-day and within-day variation in urinary iodine excretion.
abstract: OBJECTIVE
  To examine the day-to-day and within-day variation in urinary iodine excretion and the day-to-day variation in iodine intake.
  
  
  METHODS
  Collection of consecutive 24-h urine samples and casual urine samples over 24h.
  
  
  METHODS
  The study population consisted of highly motivated subjects from our Institute.
  
  
  METHODS
  Study 1: Ten healthy subjects (seven females and three males) aged 30-46 y. Study 2: Twenty-two healthy subjects (9 males and 13 females) aged 30-55 y.
  
  
  METHODS
  Study 1: 24-h urine samples were collected for four consecutive days. Study 2: Each urine voided over 24 h was collected into separate containers. In both studies dietary records were kept.
  
  
  METHODS
  Twenty-four-hour urinary iodine excretion, 24-h urinary iodine excretion estimated as I/Cr*24 h Cr and as a concentration in casual urine samples.
  
  
  RESULTS
  Study 1: Both iodine excreted in 24-h urine and iodine intake varied from day-to-day. Iodine excretion correlated with iodine intake (=-0.46, P=0.01). Iodine intake (mean 89 +/- 6.5 microg/d) was not significantly different from iodine excretion (mean 95 +/- 5.3 microg/d). Study 2: Twenty-four hour iodine excretion estimated as I/Cr*24 h Cr from the morning urine sample was significantly lower than actual 24-h iodine excretion, whereas 24-h iodine excretion estimated as I/Cr*24 h Cr from the first sample after the morning sample and the last sample before the subjects went to bed was not significantly different from actual 24-h iodine excretion. Twenty-four-hour urine excretion estimated as a concentration was lower than actual 24-h iodine excretion in casual urine taken at any time of the day.
  
  
  CONCLUSIONS
  For determination of iodine status in an individual, more than one 24-h urine sample must be used. The use of the I/Cr ratio in casual urine samples is a usable measure of iodine status if corrected for the age- and sex-adjusted 24-h creatinine excretion. Further, the study suggests that fasting morning urine samples would underestimate iodine status in this population.
authors.affiliation: Institute of Food Research and Nutrition, Danish Veterinary and Food Administration, Søborg.
authors.forename: L B
authors.initials: LB
authors.lastname: Rasmussen
authors.forename: L
authors.initials: L
authors.lastname: Ovesen
authors.forename: E
authors.initials: E
authors.lastname: Christiansen
mesh_terms: D000328:Adult; D015992:Body Mass Index; D002940:Circadian Rhythm; D003404:Creatinine / Q000652:urine; D005260:Female; D006801:Humans; D007455:Iodine / Q000008:administration & dosage / Q000652:urine*; D008297:Male; D008875:Middle Aged; D012016:Reference Values
chemical_list: D007455:Iodine; D003404:Creatinine