Intra- and Interindividual Iodine Excretion in 24 Hours in Individuals in Southern Brazil: A Cross-Sectional Study

Abstract

Aims: To evaluate the variability of 24-hour urinary iodine (UI) excretion intra- and interindividually on three days of a week in healthy subjects, living in southern Brazil, and the correlation among the urinary excretion of iodine and sodium. Methods: Cross-sectional study, including 47 volunteers: 18 individuals with one, 15 individuals with two and 14 individuals with three 24-hour urine samples. Iodine, creatinine and Na⁺ excretion in urine during 24-hour were measured. Results: Mean height, weight, BMI and 24-hour urinary excretion of creatinine were higher in men. UI and urinary sodium were correlated (n = 89, r = 0.524, p = 0.000). UI excretion varied widely, both inter- and intraindividually, on the 3 days of the week, but the mean excretion of UI was similar. In single individuals, the ratio between the maximum and minimum 24-hour UI excretion (m/m) ranged from 1.03 to 2.87, and the median coefficient of variation (CV) was 21% (P₂₅ = 7.0% and P₇₅ = 36.8%), with a range of 1%-51%. 24-hour UI excretion varied greatly among individuals on Sunday (CV = 47.5% and m/m = 7.75), Monday (CV = 38.7% and m/m = 4.60) and Thursday (CV = 40.4% and m/m = 4.50). UI was adequate in the group of 14 people, however, the UI excretion of two women suggested iodine intake persistently below that recommended by WHO. Conclusion: The variability of 24-hour UI excretion on different days in the same individual is lower than that observed among individuals.

Intra-individual and inter-individual variations in iodine intake and excretion in adult women: implications for sampling

“…Indeed, iodine excretion reflects iodine intake shortly before sampling (15) , and diet is an important factor affecting iodine intake (16) . In particular, the natural iodine content of regularly consumed iodine-containing foods and food items is highly variable (13,17) . Moreover, the bioavailability of iodine varies in different types of food (18)(19)(20) .…”

“…Moreover, the bioavailability of iodine varies in different types of food (18)(19)(20) . Diet variation among individuals is the main reason for the interindividual variation, which also results in variation in iodine excretion among different populations (17,21) . The possible reasons for population variation appear to be dietary habits, physiological metabolism, geographical environment and differences in age, weight, height, BMI and overweight status.…”

Associations between iodine intake, thyroid volume, and goiter rate in school-aged Chinese children from areas with high iodine drinking water concentrations

“…However, UIC from a single spot urine sample is not an ideal indicator of individual iodine intake because of large intra-individual variations (25), and .10 repeated spot samples or multiple 24-h urine samples from each individual are recommended to understand habitual iodine intakes (26). The 24-h UIE calculated from a 24-h urine sample is generally regarded as the optimal alternate measure for estimating iodine intake (25,27,28). Two or more 24-h urine samples are better than a single sample given intra-individual variation (29,30).…”

The Reliability of Iodine Concentration in Diaper-Retrieved Infant Urine Using Urine Collection Pads, and in Their Mothers’ Breastmilk

“…Therefore, UIC is useful as a population estimate of iodine status, but not as an individual estimate [9]. Even so, compared to the intraindividual difference, larger differences have been observed between individuals when multiple urine samples have been collected [10]. By adjusting for intraindividual variability with more than one spot-sample, the interpretability of UIC data could be improved [11].…”