Urinary iodine kinetics after oral loading of potassium iodine

Knowns and unknowns about congenital hypothyroidism: 2022 update

Several excellent guidelines and expert opinions on congenital hypothyroidism (CH) are currently available. Nonetheless, these guidelines do not address several issues related to CH in detail. In this review, the authors chose the following seven clinical issues that they felt were especially deserving of closer scrutiny in the hope that drawing attention to them through discussion would help pediatric endocrinologists and promote further interest in the treatment of CH. 1. How high should the levothyroxine (L-T4) dose be for initial treatment of severe and permanent CH? 2. What is the optimal method for monitoring treatment of severe CH? 3. At what level does maternal iodine intake during pregnancy affect fetal and neonatal thyroid function? 4. Does serum thyroglobulin differ between patients with a dual oxidase 2 (DUOX2) variants and those with excess iodine? 5. Who qualifies for a genetic diagnosis? 6. What is the best index for distinguishing transient and permanent CH? 7. Is there any cancer risk associated with CH? The authors discussed these topics and jointly edited the manuscript to improve the understanding of CH and related issues.

Studies on urinary excretion and variability of dietary iodine in healthy Japanese adults

The daily consumption of iodine in Japan is higher than in most countries, and there are few reports on iodine metabolism and variance of habitual iodine ingestion in an iodine-sufficient area. To elucidate the patterns of short-term urinary iodine excretion (UIE) and long-term variability of habitual iodine intake, the urinary iodine excretion process after a high dietary iodine load of 3 mg was observed in eight Japanese adults under strict supervision with complete urine collections for three days. In addition, estimated UIE and dietary iodine intake (DII) were assessed in 24 university students using repeated spot urine samples of ten consecutive days and a food frequency questionnaire in each of the four seasons. Approximately 50, 75 and 90% of orally ingested iodine was excreted into the urine at 8, 13 and 22 hours after ingestion, respectively. Almost an equal amount of ingested iodine in meals was cleared within 33.5 h after eating with a maximum excretion rate at 3-4 h. There was a high fluctuation in the UIE and DII in the university students. The intra- and inter-individual crude coefficients of variation were 123 or 294.7% for UIE, and 58.3 or 88.7% for DII, respectively, indicating a higher variance of habitual iodine intake than in other countries. The frequency of occurrence for UIE above 3 mg was every 43 days. Rapid renal clearance of iodine and high variability as well as low frequency of dietary iodine intake might prevent people from being exposed to an excess iodine intake over the long term in Japan.

A comparison of thyroidal protection by iodine and perchlorate against radioiodine exposure in Caucasians and Japanese

Radioactive iodine released in nuclear accidents may accumulate in the thyroid and by irradiation enhances the risk of cancer. Radioiodine uptake into the gland can be inhibited by large doses of stable iodine or perchlorate. Nutritional iodine daily intake may impact thyroid physiology, so that radiological doses absorbed by the thyroid as well as thyroid blocking efficacy may differ in Japanese with a very rich iodine diet compared to Caucasians. Based on established biokinetic-dosimetric models for the thyroid, we derived the parameters for Caucasians and Japanese to quantitatively compare the effects of radioiodine exposure and the protective efficacy of thyroid blocking by stable iodine at the officially recommended dosages (100 mg in Germany, 76 mg in Japan) or perchlorate. The maximum transport capacity for iodine uptake into the thyroid is lower in Japanese compared to Caucasians. For the same radioiodine exposure pattern, the radiological equivalent thyroid dose is substantially lower in Japanese in the absence of thyroid blocking treatments. In the case of acute radioiodine exposure, stable iodine is less potent in Japanese (ED50 = 41.6 mg) than in Caucasians (ED50 = 2.7 mg) and confers less thyroid protection at the recommended dosages because of a delayed responsiveness to iodine saturation of the gland (Wolff-Chaikoff effect). Perchlorate (ED50 = 10 mg in Caucasians) at a dose of 1000 mg has roughly the same thyroid blocking effect as 100 mg iodine in Caucasians, whereas it confers a much better protection than 76 mg iodine in Japanese. For prolonged exposures, a single dose of iodine offer substantially lower protection than after acute radioiodine exposure in both groups. Repetitive daily iodine administrations improve efficacy without reaching levels after acute radioiodine exposure and achieve only slightly better protection in Japanese than in Caucasians. However, in the case of continuous radioiodine exposure, daily doses of 1000 mg perchlorate achieve a high protective efficacy in Caucasians as well as Japanese (> 0.98). In Caucasians, iodine (100 mg) and perchlorate (1000 mg) at the recommended dosages seem alternatives in case of acute radioiodine exposure, whereas perchlorate has a higher protective efficacy in the case of longer lasting radioiodine exposures. In Japanese, considering protective efficacy, preference should be given to perchlorate in acute as well as prolonged radioiodine exposure scenarios.

Magnesium bioavailability of dried and thinly shaved kombu in rats

BACKGROUND

Magnesium (Mg) is highly bioavailable in kombu compared with other edible seaweeds. However, a considerable amount of Mg is lost during industrial processing and cooking of kombu. We hypothesized that thinly shaved kombu (TSK), a traditional Japanese kombu product, is a suitable Mg source for daily diets because TSK hardly loses Mg during processing. Rats were fed diets containing TSK or magnesium oxide (MgO) to satisfy 25%, 50%, 75%, or 100% of their Mg requirements. We determined the relative Mg bioavailability of TSK compared to MgO and examined factors affecting Mg bioavailability in TSK.

RESULTS

The relative bioavailability of Mg in TSK compared with MgO was calculated as 92.3%, 111.4%, and 87.2% from apparent absorption, urinary excretion, and femoral concentration of Mg, respectively. The ultrafiltrable Mg concentration was lower in the cecal content of rats given TSK than those given MgO. However, the mRNA expression of TRPM6, an Mg channel responsible for Mg absorption, was higher in the cecum of rats given TSK than those given MgO.

CONCLUSION

Enhancement of TRPM6 expression in the large intestine negates the low bioaccessibility of Mg in TSK, and thus TSK shows Mg bioavailability comparable with MgO. © 2020 Society of Chemical Industry.

Thyroid Blocking Policy in Hungary and Clarification of Terminology in the Light of Recommendations by International Organisations

The ambiguous terminology 'Iodine Prophylaxis' used for decades to provide iodine to the population for very different purposes as well as its replacement with 'Iodine Thyroid Blocking' is discussed and argued. Recommendations of international organisations regarding the action level for Iodine Thyroid Blocking and their implementation in national regulations in a few Member States of the European Union, and particularly in Hungary, is presented and discussed.

Inhibitory effect of low-dose inorganic iodine on thyroidal radioactive iodine uptake in healthy Japanese adults

In the event of a nuclear power plant accident, prophylactic administration of potassium iodide (KI) is recommended to prevent thyroid damage due to uptake of radioiodine. To assess the inhibitory effect of low-dose inorganic iodine on thyroidal radioactive iodine uptake (RAIU) in healthy adults without dietary iodine restriction, single or repeated doses of 10 mg inorganic iodine solution were given to 22 Japanese volunteers, 18 men and 4 women with the mean age of 35.7 years, between 2011 and 2013. Changes in urinary iodine excretion, thyroid function and 24-hour RAIU were also evaluated. The median 24-hour RAIU without iodine restriction was 13% (range, 5-26%). A single-dose of 10 mg inorganic iodine suppressed the median 24-hour RAIU measured one hour after iodine administration to 3% (range, 1-7 %) and, in 90.9% of 22 participants their 24-hour RAIU was < 5%. For seven participants given 10 mg of inorganic iodine daily for 14 days, the median 24-hour RAIU measured at 24 hours after the last administration of iodine was 6% (range, 2-12%), although the inhibitory effect was diminished in two participants. Serum thyroid stimulating hormone concentration was slightly elevated in three participants without decreased serum FT3 and FT4 levels. We conclude that a single-dose of 10 mg inorganic iodine is sufficient to inhibit RAIU in adults, although the inhibitory effect of repeated-dose on RAIU is diminished when KI is given once daily. The dose, duration or interval of iodine administration should be evaluated in iodine-sufficient regions in a future.

An assessment of the doses received by members of the public in Japan following the nuclear accident at Fukushima Daiichi nuclear power plant

The earthquake and tsunami on 11 March 2011, centred off the east coast of Japan, caused considerable destruction and substantial loss of life along large swathes of the Japanese coastline. The tsunami damaged the Fukushima Daiichi nuclear power plant (NPP), resulting in prolonged releases of radioactive material into the environment. This paper assesses the doses received by members of the public in Japan. The assessment is based on an estimated source term and atmospheric dispersion modelling rather than monitoring data. It is evident from this assessment that across the majority of Japan the estimates of dose are very low, for example they are estimated to be less than the annual average dose from natural background radiation in Japan. Even in the regions local to Fukushima Daiichi NPP (and not affected by any form of evacuation) the maximum lifetime effective dose is estimated to be well below the cumulative natural background dose over the same period. The impact of the urgent countermeasures on the estimates of dose was considered. And the relative contribution to dose from the range of exposure pathways and radionuclides were evaluated. Analysis of estimated doses focused on the geographic irregularity and the impact of the meteorological conditions. For example the dose to an infant's thyroid received over the first year was estimated to be greater in Hirono than in the non-evacuated region of Naraha, despite Hirono being further from the release location. A number of factors were identified and thought to contribute towards this outcome, including the local wind pattern which resulted in the recirculation of part of the release. The non-uniform nature of dose estimates strengthens the case for evaluations based on dispersion modelling.

High iodine intake by preschool children in Miyagi prefecture, Japan

OBJECTIVES

Standard Tables of Food Composition in Japan 2010 (FCT) remain incomplete for iodine contents. This survey was initiated to develop a method to cope with this shortage and to find daily iodine intake of preschool children in Japan.

METHODS

Data were available for one-day food intake for 296 3- to 6-year-old children (the total cases). 128 samples (the selected cases) were analyzed by ICP-MS for iodine (the measured values). Iodine intake was also calculated using FCT assuming that iodine contents in missing items were zero (the calculated values).

RESULTS

Measured and calculated values for the selected 125 cases (after exclusion of 3 extreme cases) gave geometric means (GM) of 117.6 and 101.8 μg/day. The measured/calculated ratio in GM, 117.6/101.8 = 1.155, was applied to the calculated values for total 296 cases to estimate iodine intake (the estimated values). GM for the estimated value was 175.2 μg/day and it was 8.93 μg/kg/day after adjustment for body weight for 296 children. There was no significant difference between boys and girls.

DISCUSSION

The GM values for both the measured and estimated values (n = 125 pairs) were 117.6 μg/day. The agreement suggested that the factor employed, 1.155, was proper and adequate. Literature survey suggested that values on a body weight basis were comparable between the children and adults in Japan. The levels were higher than levels in east Asian countries.

CONCLUSIONS

A correction method was developed for estimation of daily dietary iodine intake. The iodine intake level for preschoolers was comparable to levels for adult population.

Assessment of Japanese iodine intake based on seaweed consumption in Japan: A literature-based analysis

Japanese iodine intake from edible seaweeds is amongst the highest in the world. Predicting the type and amount of seaweed the Japanese consume is difficult due to day-to-day meal variation and dietary differences between generations and regions. In addition, iodine content varies considerably between seaweed species, with cooking and/or processing having an influence on iodine content. Due to all these factors, researchers frequently overestimate, or underestimate, Japanese iodine intake from seaweeds, which results in misleading and potentially dangerous diet and supplementation recommendations for people aiming to achieve the same health benefits seen by the Japanese. By combining information from dietary records, food surveys, urine iodine analysis (both spot and 24-hour samples) and seaweed iodine content, we estimate that the Japanese iodine intake--largely from seaweeds--averages 1,000-3,000 μg/day (1-3 mg/day).

Analysis of the factors associated with Tc-99m pertechnetate uptake in thyrotoxicosis and graves' disease

To determine the factors associated with 20 minute Tc-99m pertechnetate thyroid uptake, we examined all patients in whom thyrotoxicosis was diagnosed at Chiba-Hokusoh Hospital, Nippon Medical School from 2001 April through 2003 March. Patients with thyrotoxicosis diagnosed during this period were 57 with Graves' disease (76%), 11 with transient hyperthyroxinemia (TH)(14.7%), and 7 with subacute thyroiditis (SAT)(9.3%). The uptake of Tc-99m ranged from 0.97% to 40.1% in Graves' disease and from 0.15% to 0.8% in TH. Although TH may include spontaneous resolution of Graves' disease as well as painless thyroiditis, no treatment was necessary for these patients. Uptake in all patients with SAT was less than 0.5%. There were significant correlations between the level of Tc-99m uptake and the levels of free triiodothyronine (fT3), free thyroxine (fT4), thyroid-stimulating hormone (TSH)-binding inhibitory immunoglobulin (TBII), and thyroid stimulating antibody (TSAb) in patients with Graves' disease. Older patients with Graves' disease showed lower uptake than did younger patients. Both Tc-99m pertechnetate uptake and TBII levels, but not fT3, fT4 or TSAb levels, at the beginning of antithyroid drug treatment correlated significantly with the duration of treatment until the daily dose of methimazole reached 5 mg. These data suggest that Tc-99m pertechnetate uptake reflects the severity of Graves' disease and its response to the medical treatment and that antithyroid drug therapy is not necessary when the uptake is less than 0.9%.

Suppression of thyroid function during ingestion of seaweed "Kombu" (Laminaria japonoca) in normal Japanese adults

The effect of ingesting seaweed "Kombu" (Laminaria japonica) on thyroid function was studied in normal Japanese adults. Ingesting 15 and 30 g of Kombu (iodine contents: 35 and 70 mg) daily for a short term (7-10 days) significantly increased serum thyrotropin (TSH) concentrations, exceeding the normal limits in some subjects. The serum free thyroxine (FT(4)) and/or free 3,5,3'-triiodothyronine (FT(3)) concentrations were slightly decreased within the normal limits. During long term daily ingestion of 15 g of Kombu (55-87 days), the TSH levels were elevated and sustained while the FT(4) and FT(3) levels were almost unchanged. Urinary excretion of iodine significantly increased during ingestion of Kombu. These abnormal values returned to the initial levels 7 to 40 days after discontinuing the ingestion of Kombu. Based on these findings that thyroid function was suppressed during ingestion of Kombu, though the effect was reversible, we recommend Japanese people avoid ingesting excessive amounts of seaweed.