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Objective: Individual urinary iodine concentration (UIC) reflects iodine intake over a short time prior to sampling. Since eating habits are relatively constant in single subjects, UIC should be relatively constant in a given individual. The aim of our study was to verify this hypothesis by assessing UIC in repeated single urine samples from a group of healthy subjects. Design and Setting: A prospective sequential investigation was performed in 131 volunteer health workers or students recruited in our University hospital. Interventions: Single urine samples were taken in a nonfasting state, between 0900 and 1100 hours. Group 1 was composed by 131 subjects who collected one urine sample. Group 2 was composed by 11 subjects of the group 1, who collected multiple repeated urine samples (as a whole 158 urine samples, mean 14 samples each). UIC mean[plus or minus]s.d., median and coefficient of variation (CV%) was measured in both groups. Results: Interindividual UIC variation was wide, UIC ranging from 21 to 382 [mu]g/l, mean 136[plus or minus]84 [mu]g/l, median 124 [mu]g/l, CV 62%. Also in the 11 subjects repeatedly sampling there were considerable differences among individual UIC average levels (ranging from 37[plus or minus]15 to 221[plus or minus]91 [mu]g/l). However, in this second group, the intraindividual variation was considerably restricted (CV% 36). Conclusions: The present study shows that in a nonfasting state in mid-morning UIC is more stable from day to day in a single subject, depending on his eating habits, than in various subjects. Thus, a single urine sample even in nonfasting state may give some rough information about the individual's iodine status. European Journal of Clinical Nutrition (2006) 60, 421-425. doi: 10.1038/sj.ejcn.1602334; published online 14 December 2005 Keywords: thyroid, Italy, milk, diet, urinary iodine concentration, iodine supply, Author(s): B Busnardo [1]; D Nacamulli [1]; L Zambonin [1]; C Mian [1]; M Piccolo [1]; M E Girelli [1] Introduction A 24 h urinary iodine excretion (UIE) is the [...]