Studies, of iodine nutrition

Variation in urinary iodine excretion is important because it influences the study of iodine nutrition. Urinary iodine excretion exhibits large variations. The components of variation include preanalytical, analytical and biological variations. Biological variation consists of between- and within-individual variations, and can be broken down into chronobiological variation, i.e., diurnal and seasonal variations, and variations related to dilution, dietary peculiarities and supplement use. This is important for the evaluation and planning of studies of iodine nutrition, and it can be calculated that 500 urine samples depict population iodine nutrition level within 5%, while 125 urine samples are required for a value of 10%. Estimating 24h urinary iodine excretion lowers variation, and consequently the number of urine samples needed is reduced by around 20%. Similarly, it can be calculated that less than 10—15 urine samples from an individual may be misleading. 

Variation in Urinary Iodine Excretion and Studies of Iodine Nutrition... 

Populations are evaluated in the study of iodine nutrition. Population iodine excretion is described by two variables mean and variation. When describing iodine excretion in populations, a common approach is to compare mean or median values. However, this value may be identical, even though the populations differ markedly in distribution (Andersen et al, 2004), and thus differ despite similar mean values. Variance is thus another parameter to consider in the description of iodine excretion, and comparison of variances may differ from comparison of mean values. 

This reliability of studies of iodine nutrition can be estimated using the same statistics as discussed in the previous section (Fraser and Harris, 1989). Now we know the number of samples, n, while the precision range, D, is the question to be answered from Table 44.4. 

When planning a study of iodine nutrition, the number of urine samples needed to describe the iodine excretion level in a population can be read from Table 44.4 (Andersen et al., 2007a). If a precision range of 10% is aimed for, still with 95% confidence, about 125 spot urine samples are needed. Using the estimated 24 h urine iodine excretion reduced the number of samples needed by 20%, i.e., to 100 samples. A precision range of 5% required around 500 spot urine samples, while estimating 24h urinary iodine excretion reduced the required number of spot urine samples to around 400, as can be read from Table 44.4 (Andersen et al., 2007a). 

Variations in urinary iodine portray variations in iodine intake. However, huge variations in sample iodine content do not reflect similar variations in the iodine nutrition in that population. This is important for risk estimation in the evaluation of population iodine intake, and has important implications for studies of iodine nutrition. Furthermore, the reliability of studies of iodine nutrition and the number of urine samples needed to assess iodine excretion level can be calculated. 

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... 

This study has added evidence to the view that the level of iodine nutrition plays a crucial role in the intellectual development of children. 

The results from the studies of iodine status of school-children living in urban and rural areas in south Bulgaria indicated that about 50% of them had optimal iodine nutrition. Statistically significant differences were found in some of the subgroups with different iodine status, which underlines the importance of socioeconomic status and the living standard of the population for the development of IDD. 

In vitro studies on the ability of horseradish peroxidase or lacto-peroxidase to catalyze iodination of proteins at tyrosine residues are becoming quite frequent (244-248). The studies are designed either to provide better understanding of the incorporation of iodine into thyroid proteins or to develop better ways of producing radioactively labeled proteins for tracer studies. An immobilized enzyme system has been developed to achieve this second purpose (248). A large number of proteins incorporate iodine by this method which is superior to iodination with chloroamine-T or IC1. These iodinated proteins should prove invaluable in nutritional studies. 

Stewart JC, Vidor GI, Buttheld IH and Hetzel BS (1971) Epidemic thyrotoxicosis in Northern Tasmania studies of clinical features and iodine nutrition. Austral NZ J Med 1 203-211. 

This increased to 100 pg/kg when feed was supplemented with iodine (Jahreis et al., 1999). Mean concentrations in the range 100-300pg-iodine/kg milk were found in more recent studies in Germany (Bader et al, 2005 Preiss et ai, 1997 Schone et ai, 2003 Launer and Richter, 2005) and other European countries, e.g., Denmark (Rasmussen et al., 2000) and Norway (Dahl et ai, 2003)- The German Society of Nutrition s recommended daily allowance (RDA) of iodine for young people and adults is 200 pg iodine (D-A-CH, 2000). Half a liter of milk with lOOpg-iodine/ kg would provide a quarter of the RDA, but half a liter of milk with 200 pg - iodine/kg would provide half... 

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). 

The variation in urinary iodine excretion affects the reliability of estimates of population iodine nutrition. Low urinary iodine is seen in iodine-replete individuals due to random variation (Andersen et al., 2001). However, a high number of samples increases the reliability of the estimates of iodine excretion in a population, but what is the reh-ability of a study including a certain number of spot urine samples from a population ... 

The validity of the duplicate portion technique may be problematic as the completeness of duplicate portions is often difficult to assess. However, the use of biochemical markers, such as plasma, serum and urine, may be incorporated into nutritional assessment studies to validate dietary surveys or confirm nutritional status. There are a number of different methods that can be used to assess iodine status and, in particular, for the determination of the severity of iodine deficiency. However, two main methods used for the assessment of iodine status are measurement of urinary iodine excretion and thyroid function tests (an indirect method of iodine sufficiency). 

We identified eight studies worldwide that evaluated iodine nutrition in vegetarians (Abdulla et al, 1981 Draper et al, 1993 Key et al, 1992 Krajcovicova-Kudlackova et al, 2003 Lightowler and Davies, 1998 Rauma et al., 1994 Remer et al., 1999 Waldmann et al, 2003). Those studies are summarized in Table 54.6. The informational value of these studies is limited by small sample size and methodological deficiencies. For example, only four studies included more than 40 vegetarians (Draper et al, 1993 ... 

Table 54.6 Description of eight studies that evaiuated iodine nutrition in vegetarians ...

In order to study the effect of pregnant womens iodine nutritional situation on their child s development, we have isolated, as much as possible, other major determining factors, such as health assistance, maternal cultural and intellectual status, family structure, and number and order among siblings. 

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