Concept and validation of a simple model of the intrathyroidal iodine kinetics

2004 ◽  
Vol 43 (01) ◽  
pp. 21-25 ◽  
Author(s):  
F.-J. Bormuth ◽  
S. Braun ◽  
M. Zimny ◽  
H.-J. Schroth ◽  
Th. Rink
Keyword(s):  
Simple Model ◽  
Radioiodine Therapy ◽  
Iodine Content ◽  
Iodine Intake ◽  
Iodine Uptake ◽  
Average Deviation ◽  
Regression Curves ◽  
Significant Difference ◽  
Iodine Excretion ◽  
The Individual

Summary Aim of this study is the introduction and validation of a simple model of the intrathyroidal iodine kinetics, designed for optimizing radioiodine therapy planning and dose measurement in a routine clinical setting. Methods: The new model defines the intrathyroidal iodine kinetics as balance of the thyroidal iodine intake and -excretion, characterized by the two exponential equations At = A0 * (1-exp(-λ1t)) and At = A0 * (exp(-λ2t) -1), respectively. A0 describes the theoretically maximum iodine uptake when the thyroidal iodine excretion is ignored, λ1 and λ2 represent the constants characterizing the iodine intake and excretion, respectively. The thyroidal iodine content at the time t equals the sum of both functions, which is At = A0 * (exp(-λ2t)-exp(-λ1t)). In 25 patients with autonomous goiter / nodules (n = 18), Graves’ disease (n = 5), or endemic euthyroid goiter (n = 2), the iodine uptake in the thyroid during the radioiodine therapy as fraction of the applied activity was determined daily, with the remaining body covered by a lead shield. On average, 7.2 measurements were performed per patient (minimum 4, maximum 13). With these uptake values, individual regression curves were fitted using the above equation, and the difference between the actual measurements and the corresponding values of the regression curves was determined. Results: The average deviation of the 179 uptake values from the calculated points of the respective regression curves was only 1.4%. There was no significant difference between the three disease groups. The distribution of the relative deviations during the individual courses was constant, systematic errors were not detected. Conclusion: Our results suggest that the intrathyroidal iodine kinetics can be precisely described with the model At = A0 * (exp(-λ2t)-exp(-λ1t)). With only three measurements, the trend of the curve can be calculated, which allows to determine the total radioiodine storage in the thyroid.

scholarly journals Breast Milk Iodine Concentration Is Associated with Infant Growth, Independent of Maternal Weight

Nutrients ◽  
2020 ◽  
Vol 12 (2) ◽  
pp. 358 ◽  
Author(s):  
Lindsay Ellsworth ◽  
Harlan McCaffery ◽  
Emma Harman ◽  
Jillian Abbott ◽  
Brigid Gregg
Keyword(s):  
Breast Milk ◽  
Weight Status ◽  
Post Partum ◽  
Iodine Content ◽  
Iodine Concentration ◽  
Iodine Intake ◽  
Infant Growth ◽  
Maternal Weight ◽  
Significant Difference ◽  
Pregnancy Weight

In breastfed infants, human milk provides the primary source of iodine to meet demands during this vulnerable period of growth and development. Iodine is a key micronutrient that plays an essential role in hormone synthesis. Despite the importance of iodine, there is limited understanding of the maternal factors that influence milk iodine content and how milk iodine intake during infancy is related to postnatal growth. We examined breast milk samples from near 2 weeks and 2 months post-partum in a mother-infant dyad cohort of mothers with pre-pregnancy weight status defined by body mass index (BMI). Normal (NW, BMI < 25.0 kg/m2) is compared to overweight/obesity (OW/OB, BMI ≥ 25.0 kg/m2). The milk iodine concentration was determined by inductively coupled plasma mass spectrometry. We evaluated the associations between iodine content at 2 weeks and infant anthropometrics over the first year of life using multivariable linear mixed modeling. Iodine concentrations generally decreased from 2 weeks to 2 months. We observed no significant difference in iodine based on maternal weight. A higher iodine concentration at 2 weeks was associated with a larger increase in infant weight-for-age and weight-for-length Z-score change per month from 2 weeks to 1 year. This pilot study shows that early iodine intake may influence infant growth trajectory independent of maternal pre-pregnancy weight status.

Effect of voluntary intake of iodinated salt on prevalence of goitre in children

1988 ◽  
Vol 117 (3) ◽  
pp. 333-338 ◽  
Author(s):  
Gerhard Hintze ◽  
Dieter Emrich ◽  
Klaus Richter ◽  
Hanne Thal ◽  
Horst Thal ◽  
...  
Keyword(s):  
Randomized Study ◽  
Urinary Iodine ◽  
Iodine Content ◽  
Iodine Intake ◽  
Control Group ◽  
Urinary Iodine Excretion ◽  
Continuous Increase ◽  
Iodine Excretion ◽  
Group A ◽  
Goitre Prevalence

Abstract. The availability of iodinated salt containing 20 mg of iodine as iodate/kg salt consumed on a voluntary basis enabled us to investigate its effect on goitre prevalence and iodine excretion in urine in a longitudinal, prospective, randomized study over 4 years. With this salt, under the assumption of a consumption of 5 g salt per day and person, an additional intake of 100 μg of iodine can be achieved. The study was performed on initially 334 children (168 boys, 166 girls) at the age of 10 years living in an area of iodine deficiency. After 4 years, 286 children still participated in the study. Initially, goitre prevalence as assessed by palpation was found to be 30.5% (37.4% in girls and 23.8% in boys). Neck circumference was found to be significantly higher in children with goitre compared with those without (30.2 ± 1.4 vs 29.4 ± 1.4 cm; P < 0.001). Iodine excretion in the urine was significantly lower in children with goitre compared with those without (40.4 ± 16.7 μg/g creatinine vs 46.1 ± 24.9 μg/g creatinine; x ± sd; P < 0.05). The children were randomly assigned to two different groups: group A (N = 146) was asked to use iodinated salt, group B (N = 188) non-iodinated salt. Over the 4 years, a continuous increase in iodine excretion in urine could be demonstrated in group A. After 1 year, it was significantly higher than in the control group that used non-iodinated salt. After 4 years, the mean iodine excretion in children using iodinated salt was 60.1 ± 24.1 μg/g creatinine in contrast to 45.1 ± 18.6 μg/g in the control group (x ± sd; P< 0.0001). However, no decrease in goitre prevalence could be documented: after 4 years, 23.8% of the children belonging to the group using iodinated salt and 22.5% of those in the group taking non-iodinated salt had a goitre. From these observations we conclude: 1. The voluntary use of a commercially available iodinated salt containing 20 mg iodate/kg leads to a significant increase in iodine intake, measured by urinary iodine excretion. Even after 4 years, the value is far below the daily iodine intake recommended by the WHO. No decrease in goitre frequency could be assessed. 2. An increase in iodine ingestion can be achieved either by increasing the iodine content of the salt or by application of iodine by alternative measures. The safest way would be to use iodinated salt exclusively, i.e. also in the food industry and restaurants. An increase in the iodine content of the salt and its continuous voluntary use would lead to a large variation in iodine intake. A higher risk of adverse reaction, e.g. iodine-induced thyrotoxicosis, cannot be excluded in susceptible persons.

scholarly journals Iodine deficiency among Italian children and adolescents assessed through 24-hour urinary iodine excretion

2019 ◽  
Vol 109 (4) ◽  
pp. 1080-1087 ◽  
Author(s):  
Angelo Campanozzi ◽  
Irene Rutigliano ◽  
Paolo E Macchia ◽  
Gianpaolo De Filippo ◽  
Antonio Barbato ◽  
...  
Keyword(s):  
Children And Adolescents ◽  
Iodine Deficiency ◽  
Urinary Iodine ◽  
Iodine Intake ◽  
Urinary Iodine Excretion ◽  
Urinary Iodine Concentration ◽  
Age Related ◽  
Italian Regions ◽  
Significant Difference ◽  
Iodine Excretion

ABSTRACTBackgroundIodine is an essential micronutrient for intellectual development in children. Information on iodine intakes based on 24-h urinary iodine excretion (UIE) is scant, because iodine status is only assessed by the measurement of urinary iodine concentration (UIC) in spot urine samples.ObjectivesThe aim of our study was to evaluate the iodine intake of school-age children and adolescents, using UIE measurement in 24-h urine collections.MethodsThe study population included 1270 healthy subjects (677 boys, 593 girls) aged 6–18 y (mean age ± SD: 10.3 ± 2.9) from 10 Italian regions. Daily iodine intake was estimated as UIE/0.92, based on the notion that $\sim$92% of the dietary iodine intake is absorbed. The adequacy of intakes was assessed according to the Dietary Reference Values for iodine of the European Food Safety Authority (EFSA). Body mass index (BMI) and UIC were also measured for each subject.ResultsBased on the scientific opinion of EFSA, 600 of 1270 subjects (47.2%) had a lower than adequate iodine intake, with a higher prevalence among girls (54.6%) compared with boys (40.2%) (P < 0.001). Although UIE and 24-h urinary volumes increased with age (P < 0.001), a progressive decrease in the percentage of subjects with iodine excretion <100 µg/24 h (P < 0.001) was observed, without any significant difference in the percentage of subjects with UIC <100 µg/L. No significant association was detected between BMI z-score and UIE (P = 0.603) or UIC (P = 0.869).ConclusionsA sizable proportion of our population, especially girls, appeared to be at risk of iodine inadequacy. The simple measurement of UIC could lead to underestimation of the occurrence of iodine deficiency in younger children, because of the age-related smaller urine volumes producing spuriously higher iodine concentrations.

scholarly journals Studies on Endemic and Experimental Goitre

1936 ◽  
Vol 36 (2) ◽  
pp. 182-203 ◽  
Author(s):  
C. E. Hercus ◽  
H. D. Purves
Keyword(s):  
New Zealand ◽  
Potassium Iodide ◽  
Urinary Iodine ◽  
Iodine Content ◽  
Iodine Intake ◽  
Mustard Seed ◽  
Urinary Iodine Excretion ◽  
Rape Seed ◽  
Iodised Salt ◽  
Iodine Excretion

VI. Summary1. Some improvements in the determination of small quantities of iodine in biological substances are described.2. The thesis that a low iodine intake is prerequisite for goitre production is supported.3. A survey of determinations by various authors of the daily urinary iodine excretion in goitrous and non-goitrous regions leads to the conclusion that the critical level of iodine intake sufficient to suppress goitre is between 120 and 160γ per day.4. Determinations of urinary iodine excretion in New Zealand and in the non-goitrous islands of Samoa are presented which show that in the parts of New Zealand investigated the iodine intake is at a low or goitrous level.5. The result in New Plymouth, Taranaki, shows that a high content of iodine in the soil does not necessarily assure an adequate iodine intake.6. The progress of prophylaxis by iodised salt in New Zealand is reviewed, and from consumption data it is concluded that iodised salt constitutes approximately only 30 per cent, of the domestic salt consumption of New Zealand.7. To ensure a more general use of iodised salt it is recommended that the regulations be amended to provide that:(a) Ordinary domestic salt shall be iodised.(b) Non-iodised salt shall be sold only in packages labelled “Non-iodised” and with the addition “ The use of this salt exposes the user to the risk of developing goitre”.8. The results obtained hitherto with the use of iodised salt are briefly reviewed and attention drawn to some apparent failures even when iodised salt has been used for all domestic purposes. These failures are attributed to the standard for iodised salt being too low.9. It is concluded that for New Zealand a supplementation of at least 100γ per day is necessary to afford complete protection against goitre.10. To provide the necessary amount of supplementation the iodine content of iodised salt in New Zealand requires to be raised. We recommend therefore that either(a) If the domestic salt only is to be iodised the standard be fixed at from 5 to 6 parts of potassium iodide (KI) per 250,000 of salt, or(b) If iodised salt is to be used in the manufacture of bread, butter, bacon and other salted foods, the standard be fixed at from 3 to 4 parts of potassium iodide (KI) per 250,000 of salt.11. In New Zealand cabbage has not shown any marked goitrogenic activity as tested on rabbits.12. Turnip roots showed sporadically a goitrogenic activity comparable with that found for the most active samples of cabbage in other countries.13. In tests of Brassica seeds on rats, goitrogenic activity was found in rape seed, cabbage seed, steamed white mustard seed, and steamed black mustard seed.14. The activity of rape seed was destroyed by steaming.We have pleasure in acknowledging the financial help which we have received from the Sir John Roberts Endowment for Medical Research, from the Sir H. L. Ferguson Fund and from the Honorary Staff of the Dunedin Hospital, and for the co-operation of a large number of our colleagues in New Zealand and Samoa in the collection of specimens.

scholarly journals Exploration of The Lower Threshold of Iodine Intake In Southern Chinese Young Adults Based On ‘Overflow Theory’ In An Iodine Balance Study

2021 ◽  
Author(s):  
Jun Wang ◽  
Hongmin Zhang ◽  
Deqian Mao ◽  
Hongxing Tan ◽  
Wei Yu ◽  
...  
Keyword(s):  
Young Adults ◽  
Southern China ◽  
Iodine Intake ◽  
Balance Study ◽  
Mean Values ◽  
Southern Chinese ◽  
Acclimation Period ◽  
Significant Difference ◽  
Iodine Excretion ◽  
Chinese Young Adults

Abstract Background: Appropriate iodine intake for adults is essential to reduce the prevalence of thyroid diseases, but there is little research data on iodine requirement of Chinese population. This study aimed to explore the iodine requirement of young adults to maintain a healthy status based on ‘overflow theory’.Methods: Iodine-balance experiment has been performed in this project. We conducted an 18-day study consisted of a 6-day acclimation period and 3 consecutive experimental stages in 37 Chinese healthy young adults (23 female and 14 male). Each stage was consumed for 4 days. Strictly-controlled low-iodine intake diets were provided for adults in the first period, an egg or 125mL milk was added in the second and third period, respectively. The dietary samples, 24-h urine specimens and faeces of volunteers were collected daily for assessment of iodine intake and excretion in volunteers.Results: Mean values of iodine intake (22.7±3.6, 35.1±3.7, and 52.2±3.8μg/d), excretion (64.7±13.9, 62.3±12.6, and 94.3±14.5μg/d) and iodine balance (-35.2±19.5, -21.0±19.8, and -33.5±26.9μg/d) were significantly different among three periods for male (P<0.001 for all); mean values of iodine intake (16.6±3.1, 29.7±2.7, and 48.0±2.7μg/d), and excretion (47.0±9.9, 55.5±8.1, and 75.7±12.4μg/d) were significantly different among three periods for female (P < 0.001 for all). No significant difference was observed among the 3 periods for female in the iodine balance (-30.5±9.3, -25.9±7.3, and -27.6±12.1μg/d). The linear regression equation of iodine excretion on iodine intake was Y=0.979X+37.04 (male) and Y=0.895X+31.48 (female). Compared with stage 2, iodine excretion increments in stage 3 had exceeded the iodine intake increment for men. The ratio of increment was 1.675 for male when the average iodine intake was 52.2μg/d in stage 3. When the iodine excretion increment equaled to the iodine intake increment, the daily iodine intake of men was 47.0μg.Conclusion: We have evaluated the iodine requirement of young adults in southern China based on overflow theory. Our results indicate the lower limit of iodine requirement for Chinese young men is 47.0μg/d. The trial was registered at www.chictr.org.cn as ChiCTR1800014877.

scholarly journals Evaluation of iodine nutritional status during pregnancy by estimated 24-hour urinary iodine excretion: population variation range and individual accuracy

2021 ◽  
pp. 1-22
Author(s):  
Ye Bu ◽  
Yan Cai ◽  
Chunlei Ji ◽  
Chunyan Zhao ◽  
Chunyuan Tian ◽  
...  
Keyword(s):  
Nutritional Status ◽  
Pregnant Women ◽  
Urinary Iodine ◽  
Reference Interval ◽  
Iodine Intake ◽  
Urinary Iodine Excretion ◽  
Individual Level ◽  
Excessive Iodine ◽  
Iodine Excretion ◽  
The Individual

Abstract Objective: To explore the accuracy of estimated 24-hour urinary iodine excretion(24hUIEest) in assessing iodine nutritional status. Design: Fasting venous blood, 24-hour and spot urine samples were collected during the day. The urinary iodine concentration (UIC) and urinary creatinine concentration (UCrC) were measured, and the urinary iodine-to-creatinine ratio (UI/Cr), 24hUIEest, and 24-hour urinary iodine excretion(24hUIE) were calculated. At the population level, correlation and consistency between UIC, UI/Cr, 24hUIEest and 24hUIE were assessed using correlation analysis and Bland-Altman plots. At the individual level, ROC curves were used to analyse the accuracy of the above indicators for evaluating insufficient and excessive iodine intake. The reference interval of 24hUIEest was established based on percentile values. Setting: Indicator can accurately evaluate individual iodine nutrition during pregnancy remains controversial. Participants: Pregnant women (n=788). Results: Using 24hUIE as standard, the correlation coefficients of 24hUIEest from different periods of the day ranged from 0.409 to 0.531, and the relative average differences ranged from 4.4% to 10.9%. For diagnosis of insufficient iodine intake, the area under the ROC curve of 24hUIEest was 0.754, sensitivity and specificity were 79.6% and 65.4%, respectively. For diagnosis of excessive iodine intake, the area of 24hUIEest was 0.771, sensitivity and specificity were 66.7% and 82.0%, respectively. The reference interval of 24hUIEest was 58.43-597.65μg. Conclusions: 24hUIEest can better indicate iodine nutritional status at a relatively large sample size in a given population of pregnant women. It can be used for early screening at the individual level to obtain more lead time for pregnant women.

scholarly journals Relationship between dietary composition and normal body temperature and hypothermia

2020 ◽  
Vol 30 (Supplement_5) ◽  
Author(s):  
K Kimura
Keyword(s):  
Body Temperature ◽  
Thyroid Hormones ◽  
Tympanic Membrane ◽  
Iodine Intake ◽  
The Body ◽  
Tympanic Temperature ◽  
Dietary Composition ◽  
Significant Difference ◽  
Waking Up ◽  
The Individual

Abstract Background Maintaining a core temperature of 37.0 °C is important for autoimmunity, but reports in recent years show a declining trend in body temperature in Japan. The present study aimed to identify the factors leading to hypothermia by examining the relationship between dietary composition. Methods The subjects were 80 healthy females (average age: 18.2±1.0 years). We used a questionnaire format to survey the dietary pattern of the subjects. The dietary patterns were assessed by examining the average meal content consumed per week over the last 1-2 months and meal consumption, including nutritional content and other factors, using analysis software. The subjects measured their tympanic temperature using a thermometer after waking up. Correlation coefficient was calculated to determine correlations between tympanic temperature and each item. Results A significant correlation was observed between tympanic membrane temperatures upon waking up and iodine intake (r = 0.301,P&lt;0.05) as well as the adequacy ratio of iodine reference intake (ratio of iodine intake to the Dietary Reference Intakes for Japanese, r = 0.301,P&lt;0.05). A comparison between the group with tympanic membrane temperatures of ≥ 36.0 °C upon waking up and that with temperatures of &lt; 36.0 °C showed a significant difference in iodine intake (732±518μg vs 422±248μg,P&lt;0.05) and the adequacy ratio of iodine reference intake (5.6±4.0 vs 3.2±1.9,P&lt;0.05). Conclusions We examined the association of body temperature in Japanese women in their teens with their dietary composition and found a correlation between iodine intake and the adequacy ratio of iodine reference intake. Iodine is a substance essential for the production of the thyroid hormones thyroxine and triiodothyronine. Thyroid hormones regulate biochemical reactions, such as protein synthesis and enzyme activity, and play an important role in regulating metabolic activity. Therefore, iodine may influence body temperature via these hormones. Key messages Regular body temperature monitoring is recommended for the prevention of infectious diseases. When there is a decrease in the body temperature, dietary composition of the individual should be checked.

scholarly journals Assessment of Iodine Deficiency among School-Going Children of Age Group 6 to 12 Years in Kachchh District, Gujarat State: Cross-Sectional Hospital-Based Study

2021 ◽  
Author(s):  
Dinesh P. Sharma ◽  
Amitkumar Maheshwari ◽  
Chandan Chakrabarti ◽  
Darshan J. Patel
Keyword(s):  
Iodine Deficiency ◽  
Urinary Iodine ◽  
Control Program ◽  
Iodine Content ◽  
Cross Sectional Study ◽  
Iodine Intake ◽  
Urinary Iodine Excretion ◽  
Cross Sectional ◽  
Iodine Level ◽  
Iodine Excretion

Abstract Aim Iodine deficiency disorder (IDD) is the cause of preventable brain damage, mental retardation, and stunted growth and development in children. This study aimed to detect the prevalence of IDD in Kachchh district, Gujarat, by testing urinary iodine excretion levels and iodine intake of salts in school-going children. Methods A cross-sectional study was conducted and the level of iodine deficiency was assessed in 223 school children of both sexes, aged 6 to 12 years from four talukas, that is, subdivisions, of the Kachchh district by estimating urinary iodine using Sandell–Kolthoff reaction along with iodine content in edible salt samples by MBI kit (STK-Spot testing kit, MBI Kits International, Chennai, TN, India). Results The median urinary iodine level was found to be 194 μg/L, indicating no biochemical iodine deficiency in the region. In the study areas, 1% of the population showed a level of urinary iodine excretion < 50 μg/L. About 83% salt samples had iodine level more than 15 ppm and the iodine content in salt samples less than 15 ppm was only about 17%, indicating the salt samples at households contain iodine in adequate level. Conclusion There is a need of periodic surveys to assess the change in magnitude of IDD with respect to impact of iodized salt intervention.Furthermore, to strengthen National Iodine Deficiency Disorders Control Program, factors should be identified. There is also a need to prevent and reimpose the ban on the sale of noniodized salts in Gujarat.

scholarly journals Iodine in drinking water in Denmark is bound in humic substances

2002 ◽  
pp. 663-670 ◽  
Author(s):  
S Andersen ◽  
SB Petersen ◽  
P Laurberg
Keyword(s):  
Drinking Water ◽  
Humic Substances ◽  
Source Rock ◽  
Tap Water ◽  
Iodine Content ◽  
Iodine Intake ◽  
Size Exclusion ◽  
Geochemical Data ◽  
Marine Deposits ◽  
Iodine Excretion

OBJECTIVE: The iodine intake level is important for the occurrence of thyroid disorders in a population. We have previously found that iodine in drinking water is related to iodine excretion but whether iodine is present as iodide or bound in other molecules remains unknown. DESIGN: We measured iodine in drinking water from 22 locations in Denmark. Six locations were selected by iodine content for further tap water analysis (Skagen 140 micro g/l, Samsoe 56 micro g/l, Nykoebing S. 50 micro g/l, Nakskov 40 micro g/l, Ringsted 38 micro g/l, Copenhagen 19 micro g/l). METHODS: HPLC size exclusion before (Skagen) and after (all sites) freeze drying and measurement of absorbance (280 nm) and iodine in fractions, and fluorescence spectroscopy of bulk organic matter in Skagen drinking water. RESULTS: Iodine content was unaltered after 3 Years (P=0.2). All samples contained organic molecules with characteristics similar to humic substances. Most iodine eluted with humic substances (Skagen 99%, Ringsted 98%, Nykoebing S. 90%, Copenhagen 90%, Samsoe 75%, Nakskov 40%). Changing pH and ionic strength and preincubation with iodide indicated that iodine was bound in humic substances. Humic substances may affect thyroid function but differ with geology. Geological and geochemical data agree with tap water humic substances having been released from marine deposits. Iodine is abundant in the marine environment and marine deposits are particularly rich in iodine. Correlation analysis (r=0.85, P=0.03) conform to iodine in drinking water, suggesting marine humic substances at the source rock. CONCLUSION: Iodine in Danish drinking water varied considerably. In drinking water with a high iodine content, the iodine mainly eluted with humic substances derived from marine source rock. We hypothesize that iodine in drinking water in general suggests coexisting humic substances of marine origin.

scholarly journals Medical therapy of Graves' disease: effect on remission rates of methimazole alone and in combination with triiodothyronine

2000 ◽  
pp. 117-124 ◽  
Author(s):  
W Raber ◽  
E Kmen ◽  
W Waldhausl ◽  
H Vierhapper
Keyword(s):  
Randomized Study ◽  
Urinary Iodine ◽  
Antithyroid Drug ◽  
Iodine Intake ◽  
Fixed Dose ◽  
Urinary Iodine Excretion ◽  
Graves Disease ◽  
Significant Difference ◽  
Remission Rates ◽  
Iodine Excretion

In a prospective, randomized study of 135 newly diagnosed patients with hyperthyroidism due to Graves' disease we compared the effect on remission rates of additional triiodothyronine (T3) with conventional antithyroid drug therapy. To this end 114 patients were followed for at least 12 months (15.7+/-4.9, mean+/-s.d.) after the discontinuation of any therapy. After return of thyroid function to normal (8.5+/-7.4 weeks, mean+/-s.d.) patients were maintained on antithyroid medication for 9.0+/-2.5 months. They were then randomly assigned to one of three groups: group 1 (n=44) stopped methimazole, groups 2 (n=39) and 3 (n=31) continued with exogenous T3 (not exceeding 75 microgram/day in any patient) for a further 6 months either with (group 2) or without (group 3) a fixed dose of 10mg methimazole daily. The T3 dose was kept variable to keep TSH suppressed (<0. 1mU/l), which could be achieved in 82% of patients on 100% of their monthly visits. No serious side-effect requiring the discontinuation of the study occurred in any patient. Total T3, TSH-receptor antibodies and some previously suggested potential predictors of relapse including thyroid size by ultrasound, 24h urinary iodine excretion, history of cigarette smoking and ophthalmopathy were determined at the outset of the study and subsequently every 6 months (and total T3 every 4 weeks). No significant difference (P>0.05, Chi square) was seen in relapse of hyperthyroidism after a mean follow-up of 16 months (range: 12-31 months; groups 1:52%, 2:44% and 3:42%) in an area of low-to-moderate iodine intake (prevalence of 24h urinary iodine excretion <100 microgram/24h: 17 and 25% at two different measurements respectively). Concomitantly, no predictor of recurrence of disease could be identified, irrespective of treatment modality.

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