Urinary iodine excretion results

As over 90% of the body s iodine is excreted in urine, urinary excretion of iodine is currently the most commonly-used biochemical marker of iodine intake. The determination of urinary iodine excretion in 24-h urine specimens is considered to be the most reliable method (Dunn, 1993) for testing urinary iodine levels. However, the accuracy and validity of the results will depend on the completeness of the 24-h collections hence, measures to assess the completeness of such collections, e.g., urinary creatinine excretion or para-aminobenzoic acid (Gibson, 2005), should be considered. 

In 2003 the prevalence of goiter, as evaluated by ultrasound, was 4.3% and the occurrence of visible goiter was 0.4%. The median urinary iodine of a representative group of 809 children in this national study was 192p,g/l, with a variation from 162 p,g/l to 246p,g/l. The relative number of cases with urinary iodine excretion less than 100p,g/l was 7.7%. These results indicated that IDD had been reduced below the level of public health significance. 

Adaptation to iodine deficiency results in the classical inverse relation between the values of the 131 j thyroid uptake (U) and of the daily urinary iodine excretion (E). This relation has been defined by Stanbury et al. by the following equation U = 57.4 / 57.4 + E (1). 

I was fascinated by the importance of iodine excretion by the fecal route. We usually consider only urinary iodine excretion, while your results show that the fecal excretion may play an important role. 

In 1988 the urinary iodine excretion was examined in samples of the male population, in 9 low-incidence and in 8 high-incidence areas. Afternoon spot urine was collected and analyzed with Technicon Auto-Analyzer. The result was converted to microg/24 hours iodine in the urine. Table 4 shows the results. 

These studies were somewhat hampered by the lack of knowledge on the frequency of individual iodine supplementation in the form of daily intake of iodine containing vitamin/mineral tablets. Such tablets are commonly employed in Denmark and many brands contain 150 Mg iodine. For a correct interpretation of the results it is necessary to know whether a person participating in a survey takes such tablets. Normally the iodine intake in an area is considered sufficient if the median urinary iodine excretion exceeds a certain value. If a substantial proportion of the population is taking regular iodine supplementation, this may lead to a median excretion vjdue well about what is considered a critical level, and still leave the part of the population which is not taking iodine at risk. 

The results show a strong correlation (r = 0.90, p < 0.01) in all groups between the changes in thyroid volume and the urinary iodine excretion. The maximal therapeutic effect (25 % reduction in volume) was achieved after 3 or 6 months and was maintained over the rest of the period despite a great variability in the compliance, which was best in those patients whose dose consisted of only one tablet per day. Taking into account the iodine excretion and the compliance of patients we found no statistically significant differences among the three kinds of therapy with respect to their therapeutic success. 

In the most simplistic physiological model, inadequate intake of iodine results in a reduction in thyroid hormone production, which stimulates increased TSH production. TSH acts directly on thyroid cells, and without the ability to increase hormone production, the gland becomes hyperplastic. In addition, iodine trapping becomes more efficient, as demonstrated by increased radioactive iodine uptake in deficient individuals. However, this simplistic model is complicated by complex adaptive mechanisms which vary depending on the age of the individual affected. In adults with mild deficiency, reduced intake causes a decrease in extrathyroidal iodine and reduced clearance, demonstrated by decreased urinary iodine excretion, but iodine concentration in the gland may remain within normal limits. With further reduction in intake, this adaptive mechanism is overwhelmed, and the iodine content of the thyroid decreases with alterations in iodination of thyroglobulin, in the ratio of DIT to MIT, and reduction in efficient thyroid hormone production. The ability to adapt appears to decrease with decreasing age, and in children the iodine pool in the thyroid is smaller, and the dynamics of iodine metabolism and peripheral use more rapid. In neonates, the effects of iodine deficiency are more directly reflected in increased TSH. Diminished thyroid iodine content and increased turnover make neonates the most vulnerable to the effects of iodine deficiency and decreased hormone production, even with mild deficiency. 

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. 

More iodine is present in the urine (five times the normal) and feces of hyperthyroid patients than of normal individuals. Yet, if radioactive iodine is administered to hyperthyroid individuals, the urinary exretion of the hormone is less than in normal persons freshly administered iodine is apparently retained in the body. The reduced excretion of radioactive iodine probably results from greater uptake of radioiodine in the thyroid this increase in thyroidal uptake of radioiodine is consistently observed in patients with hyperthyroidism after oral or intravenous administration of radioiodine. Thyroid slices obtained from hyperthyroid patients clear the iodine from the medium at a much faster rate that slices obtained from normal individuals. 

Table 1 shows previous reports on urinary iodide excretion, and the results were divided into those of outpatients and inpatients on regular diet and patients on iodine-restricted diet. Averages of urinary iodide excretion were from 739 to 3,286 pig/day on regular diet and less than 200 pg / day on iodine restricted diet (2-8)... 

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