Urinary iodine concentrations

A 68-year-old man was treated for a subcutaneous infection of the thigh by subcutaneous irrigation with povidone iodine (71). Toxic plasma and urinary iodine concentrations were associated with abnormalities of cardiac conduction, lactic acidosis, acute renal insufficiency, hypocalcemia, and thyroid dysfunction. 

Slovakia and urinary iodine concentrations were similar in the worker and control groups (data not... 

Caldwell, K. L., Jones, R., Hollowell, J. G. (2005). Urinary iodine concentration United States National Health and Nutrition Examination Survey 2001—2002. Thyroid. 15 692—699. 

An estimation of iodine level in a spontaneous urine sample is not representative of iodine intake over a one-week period, as urinary iodine concentrations vary daily by > 50% about the arithmetic mean of the weekly iodine intake (Anke et al. 2000, Bauch 1985). 

Delange F, De Benoist B and Burgi H (2002) Determining median urinary iodine concentration that indicates adequate iodine intake at population level. Bulletin of the World Health Organization 2002, 80 633-636. 

There are various well-established biomarkers of intake and/or nutritional status of numerous food components (Margetts and Nelson, 1997 Wilett, 1998). In the case of iodine, a good measure of iodine intake is urinary excretion, because most (more than 90%) of iodine ingested is excreted in urine. Thus, the urinary iodine concentration, even in casual urine samples, is a good marker of iodine nutrition. Urinary iodine concentration varies with fluid intake, so these values have limited use for casual samples from an individual, but they are well-suited for assessing a population group, because individual variations tend to average out. 

Figure 28.5 shows the iodine concentrations in urine and milk from nonsmoking and smoking mothers, and in urine from their neonates. Whereas urinary iodine concentrations were not different between groups of mothers, the iodine content of breast milk and of neonatal urine was reduced to around 50% if the mother was a smoker. This effect of smoking varied with the cotinine concentrations in mothers, and with the levels of thiocyanate in serum from the mothers and in cord serum (Laurberg et al., 2004). 

Figure 28.6 Maternal smoking and neonatal iodine nutrition. Breast-milk iodine and infant s urinary iodine content expressed as fraction of the mother s urinary iodine concentration. Both are measures of iodine transfer from mother to child during breastfeeding. The infant s urinary iodine content is expressed as a fraction of miik iodine content and is an inverse measure of iodine retention in the infant. Reproduced from Laurberg et al., (2004) with permission.

Since the fortification of cattle fodder started in 1950, iodine deficiency has been assumed to be eradicated in Norway (Frey, 1986). Although there never has been systematic monitoring of iodine nutrition, several studies in the last decade have shown that the iodine intake in the majority of the population is in the range considered to be sufficient. The majority of studies conducted in Norway have focused on urinary iodine concentrations in selected groups of the population. Calculation of iodine intake based on a food-frequency questionnaires covering the habitual diet in a representative sample of adult Norwegians confirmed that milk and dairy products are a very important iodine source in the diet. The study showed... 

Urinary iodine concentration in small groups of adults indicates sufficient iodine intake. 

Conceptually the whole field of iodine nutrition may be subdivided into two broad subdivisions, the process and the impact (or outcome) fields of iodine nutrition, each with its own assessment indicators. The impact side of the iodine nutrition field represents the response of the human body to the iodine delivered to and consumed by the consumer, and therefore follows the process phase sequentially. This response of the human body is usually assessed in terms of impact indicators, such as the median urinary iodine concentration, thyroid size, and blood constituents such as thyroid-stimulating hormone, thyroglobulin, or other thyroid hormones. The process side of iodine nutrition covers factors playing a role in the delivery of iodine to the consumer via iodized salt or via an alternative source, such as processed food, drinking (iodine-containing cleaning agents) used in the dairy industry water or iodophors. 

Previous studies (as mentioned above) demonstrated an improvement in the general iodine supply in different areas and different age groups. The underlying reasons for this improvement (e.g., altered nutrition, use of iodinated salt) and its consequences for thyroid pathologies are not always obvious. To clearly assess a populations iodine status, the WHO recommended monitoring the iodine content in salt at the production level, measurement of urinary iodine concentration and carrying out surveys in large cohorts under local circumstances as the most suitable method for iodine status assessment (WHO, 2001). 

Figure 44.2 is based on the same data as (Andersen et ai, 2001), and illustrates that individual mean values vary (Andersen et ai, 2003). The difference between individual mean urinary iodine concentrations is highly significant (Kruskal—Wallis test p < 0.001 for all variables), compared to that of TSH in serum (Andersen et al., 2001). This is consistent with other findings of marked differences in urinary iodine excretion between individuals (Rasmussen et ai, 1999 Busnardo et ai, 2006). 

Table 44.2 Variation in urinary iodine concentrations and estimated 24 h urinary iodine excretion in individuai sampies and in average annuai vaiues over 1 year...

Table 44.2 shows measures of dispersion of urinary iodine concentration, and includes estimated 24 h urinary iodine excretion both for individual samples and for the average of 12 monthly samples. 

It can be observed from Table 44.2 that the variation in iodine content is markedly higher among individual urine samples than the variation in average annual urinary iodine concentration. In comparison, CV% is 2.4 times larger for spot urine iodine concentration than for the average annual iodine content. This difference is 2.7 for interquartile range (IQR) (Andersen et al, 2001). 

In an intervention study with schoolchildren 8—10 years old in Malawi, Furnee et al. (1997) examined the relationship of intestinal parasite treatment and oral iodized oil efficacy. Severely iodine-deficient schoolchildren with a single parasitic infestation, either A. lumbricoides (n = 44), hookworm (n = 42), or Entamoeba histolytica (n = 24), were randomly allocated to receive or not receive treatment before taking a 1ml oral supplement (490 mg Iodine) of iodized ethyl esters from poppyseed oil. After supplementation, urinary iodine concentrations were measured regularly, to define time intervals indicating moderate iodine deficiency before urinary iodine concentrations returned to 0.40 mmol/1. Treatment with metronidazole for E. histolytica increased the protection period from 2.0 to 21.0 weeks P < 0.05). For all untreated children, the duration effect was 9.2 weeks shorter P < 0.001) than for their treated peers (16.8 weeks). They concluded that, by interfering with absorption, intestinal parasitic infestations reduce the efficacy of oral supplementation with iodized ethyl esters (Table 52.8). 

Urinary iodine concentrations in Tibet are very similar to values observed in Central Africa, but selenium deficiency is more severe in Tibet than in Central Africa. In Tibet up to 38% of school children had undetectable... 

Urinary iodine concentrations in Tibet are very similar to those observed in Sudan (Moreno-Reyes et ai, 1993), but the frequency of goiter or hypothyroidism is lower. The lack of goitrogens in Tibet probably explains the lower frequency of hypothyroidism and goiter despite similar urinary iodine concentrations to those in Central Africa. Experimentally, the involvement of thiocyanate in the pathogenesis of myxedematous cretinism has recently been corroborated (Contempre et al, 2004). 

Figure 71.2 Distribution of urinary iodine concentrations in 557 subjects from 12 villages in Lhasa Prefecture, Tibet. Fourteen percent had urinary iodine concentrations <0.6rrg/dl, 66% had concentrations <2rrg/dl, and 95% had concentrations <5ri,g/dl. The numbers on the horizontal axis represent the midpoint of the intervals shown. To convert values for urinary iodine to nanomoles per liter, multiply by 78.7. Reproduced with permission from Moreno-Reyes eta/, (1998). Massachusetts Medical Society.

In this cross-sectional study, KBD was associated with iodine deficiency in Tibet and this association persisted when age and sex were controlled for by multivariate analysis. The risk of KBD appeared to be greater for subjects with more severe iodine deficiency, i.e., lower urinary iodine concentrations and higher serum TSH concentrations (Moreno-Reyes et ai, 1998). The severity of iodine deficiency in Tibet makes iodine-supplementation programs mandatory. 

Figure 71.11 Urinary iodine concentrations after iodine and seienium suppiementation. Mean urinary iodine concentrations in the piacebo-iodine suppiemented subjects (O) and in the seienium-iodine-suppiemented subjects ( ) over time. The reference range for iodine urinary concentrations is situated above the dotted iine. Bars indicate vaiues 1 SE beiow and 1 SE above the mean on the iogarithmic scaie. There was a significant main effect of time [P < 0.001). Significantiy different from aii subsequent vaiues (Heimert contrasts). Reproduced with permission from Moreno-Reyes et al., (2003). The American Society for Nutrition.

Table 74.4 Epidemiological criteria for assessing iodine nutrition based on median urinary iodine concentrations in school-aged children...

Urinary iodine concentration and palpation of goiter among schoolchildren is the most frequent method used by cross-sectional surveys to measure iodine deficiency. Because iodine is excreted by the kidneys, the urinary concentration of iodine is an indicator of iodine intake. Lower production of thyroxine leads to increased production of the thyroid-stimulating hormone, which results in thyroid hyperplasia known as goiter. The World Health Organization (2001) classifies iodine deficiency into mild, moderate and severe when urinary excretion is, respectively, 50—99, 20 9 and <20 p,g/l of urine. 

Table 83.4 Urinary iodine concentration (UiC) in aduits iiving in different parts of Poiand...

After iodization, there has been an increase in urinary iodine concentration, an increase in plasma inorganic iodine level and a decrease in thyroid iodine clearance and radioiodine uptake by the thyroid gland in normal subjects. 

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