**2.5.6 Urine**

376 Macro to Nano Spectroscopy

higher than those values which were found in the literature. No correlation of iodine content

The inorganic form of iodine represents about 0.5 % of the total plasma iodine. The rest occurs in bound form with specific plasma protein (protein - bound iodine, PBI) which has gained wide use as an indicator of thyroid activity in humans. It has been reported that the total plasma iodine concentration in healthy subjects is between 40 and 80 μg/l. According to Allain's studies when plasma iodine concentrations are below 40 μg/l, hypothyroidism is highly likely, when they are between 80 and 250 μg/l, hyperthyroidism, particularly Graves' disease is probable. Above 250 μg/l – iodine overload is almost certainly indicated

Despite the fact that iodine is one of the most important essential elements, the quantitative data on its concentration in the human brain is really scarce. The nature and site of iodine binding in the human brain is still unknown. The results of Andrasi et al. (Andrási et al., 2004) investigations on iodine distribution between the lipid fraction and in the brain tissue without lipid have indicated that its mean contents vary between 910 ± 147 ng/g dry weight and 281 ± 68 ng/g dry weight depending on the brain region (the highest content was found

Levine et al. (Levine et al., 2007) presented a study on determining iodine concentration in tiny (less than 25 mg) human hair samples. Iodine concentrations from the blinded hair autism study samples ranged from 0.483 to 15.9 µg/g. In Adams' et al. studies (Adams et al., 2006) the mean concentration of iodine in the hair of autistic children has been reported to be lower than in the hair from the control group children. The low level of iodine in the hair of children with autism suggests that iodine could be important in the aetiology of autism,

molecular weight iodine containing molecules (Braetter et al., 1998) account for the remaining 20%. European breast milk samples have been determined to contain 95 ± 60 μg/l total iodine. The total iodine content varied depending on the lactation state, and iodine was associated with fat at approximately 30% and 70% of the low molecular weight fraction (Michalke, 2006). A study of iodine species in milk samples obtained from humans from several different European countries and in infant formulas from different manufacturers was carried out by Fernández-Sanchez and Szpunar (Fernández-Sanchez & Szpunar, 1999). The authors also developed a method to determine iodine in human milk and infant formulas using ICP-MS. In the human milk the values found were between 144 ± 93.2 μg/ kg, whereas in the infant formulas the values were 53.3 ± 19.5 (Fernández-Sánchez et al.,

, while, mainly, another six high

with the age or weight of the healthy gland was observed.

in susbstantia nigra and the lowest in vermis crebelli).

presumably due to its effect on thyroid function.

Approximately 80% of iodine in human milk is present as I-

**2.5.2 Plasma** 

(Allain et al., 1993).

**2.5.3 Brain** 

**2.5.4 Hair** 

**2.5.5 Human milk** 

2007).

In urine, iodine occurs as I- , but some organic species can also be found. Urinary iodine concentration is the prime indicator of nutritional iodine status and is used to evaluate population-based iodine supplementation. In 1994, WHO, UNICEF and ICCIDD recommended median urinary iodine concentrations for populations of 100- 200 µg/l, assuming the 100 µg/l threshold would limit concentrations <50 µg/l to </=20% of people (Delange et al., 2002). During the period between the years 1994-2002, the urinary iodine concentration was determined in 29,612 samples at the Institute of Endocrinology in the Czech Republic. The mean basal urinary iodine concentrations +/-SD were 115+/-69 μg/l. Out of all the samples, 0.7% were in severe (<20 μg/l), 9.6% in moderate (20-49 μg/l), 40.1% in mild (50-99 μg/l), 35.6% in adequate (100-200 μg/l), and 14.0% in more than adequate (>200 μg/l) subsets of iodine nutrition. A statistically significant (p<0.00001) difference was found between the mean male (127 μg/l) and female (112 μg/l) urinary iodine, and an inversely proportional trend also existed in the age-related data (Bílek et al., 2005). It is also known that patients with iodine induced hyperthyrosis have 10- to 100-fold more urinary iodide than healthy patients (Mura et al., 1995).

Delange et al. (Delange et al., 2002) determined the frequency distribution of urinary iodine in iodine-replete populations (schoolchildren and adults) and the proportion of concentrations <50 µg/l. The findings were as follows: nineteen groups reported data from 48 populations with median urinary iodine concentrations >100 µg/l. The total population was 55 892, including 35 661 (64%) schoolchildren. Median urinary iodine concentrations were 111-540 (median 201) µg/l for all populations, 100-199 µg/l in 23 (48%) populations and >/=200 µg/l in 25 (52%). The frequencies of values <50 µg/l were 0-20.8 (mean 4.8%) overall and 7.2% and 2.5% in populations with medians of 100-199 µg/l and >200 µg/l, respectively. The frequency reached 20% only in two places where iodine had been supplemented for <2 years. According to the authors' conclusions the frequency of urinary iodine concentrations <50 µg/l in populations with median urinary iodine concentrations >/=100 µg/l has been overestimated, and the threshold of 100 µg/l does not need to be increased. The main conclusion of the cited work was that in populations, median urinary iodine concentrations of 100-200 µg/l indicate adequate iodine intake and optimal iodine nutrition.

According to Verheesen and Schweitzer (Verheesen and Schweitzer, 2011) the threshold of 100 μg/l is only to make sure that severe iodine deficiency (beneath 50 µg/l) is not present in more than 20% of the population. Although the WHO is concerned about the negative effects of even mild iodine deficiency, the 100 μg/l threshold was never intended to prevent mild iodine deficiency. In order to combat mild deficiency the threshold should be reconsidered. The authors also emphasized the need to test for other biomarkers in individual cases in order to be able to adequately establish iodine deficiency. Since there is a lack of trusted biomarkers, thus far statistics have been used to estimate the percentage of the population being deficient, instead of showing prevalence figures. Furthermore, population figures are typically described only by a median; variables such as % being deficient, % being pregnant, % women, % men and age related figures should be thoroughly investigated.
