Higher Urine Volume Results in Additional Renal Iodine Loss
ABSTRACT For some endocrine and nutritional biomarkers, for example, cortisol and vitamin B(12), significant associations between 24-hour renal analyte excretion and the respective 24-hour urine volume (U-Vol) have been reported. Therefore, our objective was to investigate whether 24-hour U-Vol (a marker of fluid intake) is also a relevant influencing factor of absolute daily iodine excretion.
Urinary iodine excretion rates were measured in repeatedly collected 24-hour urine samples of (i) 9 healthy women participating in a controlled diet experiment with constant iodine intake and (ii) 204 healthy free-living adolescents (aged 13-18 years) who performed the respective urine collection during 2003-2008. Associations between U-Vol (L) and renal iodine excretion (μg/24 h) were investigated cross sectionally (multiple linear regression model, PROC GLM) and longitudinally (repeated-measures regression models, PROC MIXED). The major iodine sources in the adolescent's diet (iodized salt, milk, fish, eggs, and meat) were controlled for.
Urinary iodine excretion was significantly associated with 24-hour U-Vol in all performed fully adjusted regression models. A 1-L increase of U-Vol predicted an additional 15.0 μg/day (adolescents, 95% confidence interval: [9.8, 20.0], p < 0.0001) and 16.5 μg/day (women, 95% confidence interval: [9.2, 23.7], p = 0.0002) increase in iodine excretion. The longitudinal analysis in adolescents revealed a stronger relation of iodine excretion with U-Vol in girls than in boys (β = 17.1 vs. β = 10.5).
A high fluid consumption, and thus a high U-Vol, could lead to an additional renal iodine loss that obviously cannot be compensated by the iodine contents of non-milk-based beverages, reported to amount to ∼4 μg/L, on average. For specific research questions using the biomarker 24-hour urinary iodine excretion, U-Vol should therefore be considered as a potential confounder.
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ABSTRACT: An objective noninvasive biomarker for fruit and vegetable (FV) consumption would help to more reliably characterize the relationship between FV intake and health status in observational studies. Because increases in urinary hippuric acid (HA) were observed after consumption of several FV varieties, we aimed to investigate whether 24-h urinary HA may represent a potential biomarker for FV consumption in children and adolescents. The association of FV and juice (FVJ) intake calculated from 3-d weighed dietary records with 24-h urinary HA excretion was analyzed in 240 healthy children and adolescents and compared with associations of the established biomarkers urinary nitrogen (uN) and urinary potassium (uK) with protein and potassium intake, respectively. Spearman correlation coefficients (r) and cross-classifications were calculated for all diet-biomarker associations. Potential confounders for the HA-FVJ association were examined in linear regression models. In children, correlations of HA with FVJ (r = 0.62), uN with protein (r = 0.64), and potassium intake with uK (r = 0.65) were comparable. In adolescents, the HA-FVJ association was weaker (r = 0.41) compared with the biomarkers uN (r = 0.60) and uK (r = 0.58) (all P < 0.0001). Cross-classification into the same/adjacent quartile by dietary and urinary data were >85% for all analyzed comparisons except for a 75% classification agreement between HA and FVJ in adolescents. Unadjusted and adjusted linear regression models indicated significant (P < 0.0001) HA-FVJ associations in both age groups. FVJ explained more of the variability in HA excretion in children (R(2) = 0.38) than in adolescents (R(2) = 0.22). Our findings in children showing HA-FVJ associations comparable to those for well-established biomarkers with their respective dietary intakes suggest that HA may represent a useful biomarker for FVJ.Journal of Nutrition 05/2012; 142(7):1314-20. DOI:10.3945/jn.112.159319 · 4.23 Impact Factor
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ABSTRACT: Iodine status has been historically assessed by palpation of the thyroid and reported as goiter rates. Goiter is a functional biomarker that can be applied to both individuals and populations, but it is subjective. Iodine status is now assessed using an objective biomarker of exposure, i.e., urinary iodine concentrations (UICs) in spot samples and comparison of the median UIC to UIC cut-offs to categorize population status. This has improved standardization, but inappropriate use of the crude proportion of UICs below the cut-off level of 100 µg/L to estimate the number of iodine-deficient children has led to an overestimation of the prevalence of iodine deficiency. In this review, a new approach is proposed in which UIC data are extrapolated to iodine intakes, adjusted for intraindividual variation, and then interpreted using the estimated average requirement cut-point model. This may allow national programs to define the prevalence of iodine deficiency in the population and to quantify the necessary increase in iodine intakes to ensure sufficiency. In addition, thyroglobulin can be measured on dried blood spots to provide an additional sensitive functional biomarker of iodine status.Nutrition Reviews 10/2012; 70(10):553-70. DOI:10.1111/j.1753-4887.2012.00528.x · 5.54 Impact Factor
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ABSTRACT: PURPOSE: Even mild iodine deficiency may negatively affect cognitive performance, especially at a young age. Our aim was to investigate iodine status in very young children and to assess the importance of iodized salt in processed foods of which the use has decreased during the last years in Germany. METHODS: Twenty-four hours urinary iodine excretion (UIE) as a marker of iodine intake was measured in 378 24 h urine samples collected 2003-2010 by 221 3 to <6 years old participants of the DONALD Study. Parallel 3-d weighed dietary records and measurements of urinary sodium excretion provided data on the daily consumption of the most important iodine sources in the children's diet (iodized salt, milk, fish, meat and eggs). Time trends of UIE (2003-2010) and contributions of the different food groups were analyzed by using linear mixed-effects regression models. RESULTS: Median UIE of 71 μg/d in boys and 65 μg/d in girls (P = 0.03), corresponding to an iodine intake of 82 and 75 μg/d, respectively (assumption: 15 % non-renal iodine losses), was below the recommended dietary allowance (RDA) of 90 μg/d. Milk, salt and egg intake were significant predictors of UIE; milk and salt together accounted for >80 % of iodine supply. Between 2003 and 2010, UIE decreased significantly by approximately 1 μg/d per year. The contribution of salt intake to UIE decreased from 2003-2006 to 2007-2010. CONCLUSION: In countries where salt is a major iodine source, already modest decreases in the iodized proportion of salt used in processed foods may relevantly impair iodine status even in preschool children.European Journal of Nutrition 12/2012; DOI:10.1007/s00394-012-0474-6 · 3.84 Impact Factor