Goitrogens in food and water

Genetics and bitter taste responses to goitrin, a plant toxin found in vegetables

The perceived bitterness of cruciferous vegetables such as broccoli varies from person to person, but the functional underpinnings of this variation are not known. Some evidence suggests that it arises, in part, from variation in ability to perceive goitrin (5-vinyloxazolidine-2-thione), a potent antithyroid compound found naturally in crucifers. Individuals vary in ability to perceive synthetic compounds similar to goitrin, such as 6-propyl-2-thiouracil (PROP) and phenylthiocarbamide (PTC), as the result of mutations in the TAS2R38 gene, which encodes a bitter taste receptor. This suggests that taste responses to goitrin itself may be mediated by TAS2R38. To test this hypothesis, we examined the relationships between genetic variation in TAS2R38, functional variation in the encoded receptor, and threshold taste responses to goitrin, PROP, and PTC in 50 subjects. We found that threshold responses to goitrin were associated with responses to both PROP (P = 8.9 x 10(-4); r(s) = 0.46) and PTC (P = 7.5 x 10(-4); r(s) = 0.46). However, functional assays revealed that goitrin elicits a weaker response from the sensitive (PAV) allele of TAS2R38 (EC(50) = 65.0 μM) than do either PROP (EC(50) = 2.1 μM) or PTC (EC(50) = 1.1 μM) and no response at all from the insensitive (AVI) allele. Furthermore, goitrin responses were significantly associated with mutations in TAS2R38 (P = 9.3 × 10(-3)), but the same mutations accounted for a smaller proportion of variance in goitrin response (r(2) = 0.16) than for PROP (r(2) = 0.50) and PTC (r(2) = 0.57). These findings suggest that mutations in TAS2R38 play a role in shaping goitrin perception, but the majority of variance must be explained by other factors.

Endemic goitre and excessive iodine in urine and drinking water among Saharawi refugee children

Objective

To assess the prevalence of enlarged thyroid volume (Tvol) in Saharawi refugee children, and their urinary iodine concentration (UIC), and to identify possible sources of excess iodine intake.

Design

A cross-sectional survey was performed during January–February 2007. Tvol was measured by ultrasound and iodine concentration was analysed in casual urine samples, in household drinking water and in milk samples from household livestock.

Setting

The study was undertaken in four refugee camps in the Algerian desert.

Subjects

The subjects were 421 Saharawi children, 6–14 years old.

Results

Enlarged Tvol was found in 56 % (Tvol-for-age) and 86 % (Tvol-for-body-surface-area) of the children. The median (25th percentile–75th percentile, P25–P75) UIC was 565 (357–887) μg/l. The median (P25–P75) iodine concentration in household drinking water was 108 (77–297) μg/l. None of the children had UIC below 100 μg/l, 16 % had UIC between 100 and 299 μg/l, and 84 % had UIC above 300 μg/l. There was a positive association between Tvol and whether the household possessed livestock.

Conclusions

The children are suffering from endemic goitre and high UIC caused probably by an excessive intake of iodine. The excessive iodine intakes probably originate from drinking water and milk.

Iodine intake as a determinant of thyroid disorders in populations

Depending on the availability of iodine, the thyroid gland is able to enhance or limit the use of iodine for thyroid hormone production. When compensation fails, as in severely iodine-deficient populations, hypothyroidism and developmental brain damage will be the dominating disorders. This is, out of all comparison, the most serious association between disease and the level of iodine intake in a population. In less severe iodine deficiency, the normal thyroid gland is able to adapt and keep thyroid hormone production within the normal range. However, the prolonged thyroid hyperactivity associated with such adaptation leads to thyroid growth, and during follicular cell proliferation there is a tendency to mutations leading to multifocal autonomous growth and function. In populations with mild and moderate iodine deficiency, such multifocal autonomous thyroid function is a common cause of hyperthyroidism in elderly people, and the prevalence of thyroid enlargement and nodularity is high. The average serum TSH tends to decrease with age in such populations caused by the high frequency of autonomous thyroid hormone production. On the other hand, epidemiological studies have shown that hypothyroidism is more prevalent in populations with a high iodine intake. Probably, this is also a complication to thyroid adaptation to iodine intake. Many thyroid processes are inhibited when iodine intake becomes high, and the frequency of apoptosis of follicular cells becomes higher. Abnormal inhibition of thyroid function by high levels of iodine is especially common in people affected by thyroid autoimmunity (Hashimoto's thyroiditis). In populations with high iodine intake, the average serum thyroid-stimulating hormone (TSH) tends to increase with age. This phenomenon is especially pronounced in Caucasian populations with a genetically determined high tendency to thyroid autoimmunity. A small tendency to higher serum TSH may be observed already when iodine intake is brought from mildly deficient to adequate, but there is at present no evidence that slightly elevated serum TSH in elderly people leads to an increase in morbidity and mortality.

CONCLUSION

Even minor differences in iodine intake between populations are associated with differences in the occurrence of thyroid disorders. Both iodine intake levels below and above the recommended interval are associated with an increase in the risk of disease in the population. Optimally, iodine intake of a population should be kept within a relatively narrow interval where iodine deficiency disorders are prevented, but not higher. Monitoring and adjusting of iodine intake in a population is an important part of preventive medicine.

Speciation of iodine in high iodine groundwater in china associated with goitre and hypothyroidism

Iodine intake affects the occurrence of disease in a population. Excessive iodine intake may be caused by a high iodine content of drinking water. Tap water in few locations in Europe contains up to 139 microg/L mostly bound to humic substances, probably leaching from marine sediments in the aquifers. Even higher iodine contents have been found in Chinese waters, previously shown to associate with goitre and hypothyroidism. The aims were to elucidate speciation of high iodine groundwater from deep wells in China and to compare with high iodine waters from Europe. Water was sampled from eight wells in five villages along Bohai Bay, China. Macro-molecules and low molecular weight (MW) substances were separated by size exclusion chromatography (high performance liquid chromatography, Superose 12 HR 10/30, buffer 0.1 M Tris, pH 7.0). Organic material was evaluated by A280 and iodine in fractions measured by the Ce/As method after alkaline incineration. Iodine content of well water varied from 135 to 880 microg/L (median 287 microg/L). The amount of organic material in water was low with A280, <1-5 mAU. The chromatographic traces were similar between samples: One peak of iodine eluted around K (AV) 0.65 corresponding to MW 5 kDa (humic substances) and one peak at V (total) (iodide/low MW substances). The fraction of iodine in macro-molecules, suggested to be humic substances, varied from 8% to 70% (median 27%). Iodine and peak absorbance were associated (p = 0.006). In conclusion, iodine in iodine-rich deep well water in northern China may have marine origin and may associate with humic substances, comparable to shallow well iodine-rich water in Europe. High iodine intake from iodine-rich water suggests the cause of endemic goitre and hypothyroidism in some areas in China being iodine.

Iodine nutritional status of children on the island of Tanna, Republic of Vanuatu

OBJECTIVE

To evaluate the iodine nutritional status of children living on the island of Tanna, Republic of Vanuatu.

DESIGN

Cross-sectional study. Urine and household salt samples were collected for iodine measurement. Thyroid volumes were measured by ultrasound. A food consumption frequency survey was carried out, particularly in relation to salt, iodine-rich foods and foods that containing thiocyanate, a potentially goitrogenic substance. Urinary thiocyanate levels were also measured.

SETTING

Island rural communities in Tanna, Vanuatu.

SUBJECTS

One hundred and fifty-three schoolchildren between 8 and 10 years of age from four locations on the island participated.

RESULTS

The median urinary iodine excretion (UIE) among the children was 49 mg/l, indicating moderate iodine deficiency. This was corroborated by 27% of boys and 33% of girls having thyroid glands greater than the international standard for their age, and 36% of boys and 45% of girls having thyroid glands greater than the international standard for their body surface area based on ultrasonography. There was a highly statistically significant inverse correlation between thyroid volume and UIE for boys and girls (r = -0.444, P = 0.001 and r = -0.319, P = 0.005, respectively). There was no correlation between thiocyanate and UIE or thyroid volume. Only 34% of children reported to consume fish (tinned or fresh) on a weekly basis.

CONCLUSIONS

Against the common perception, the study has demonstrated that the children on the island of Tanna were in a state of moderate iodine deficiency. More data need to be collected from other Pacific Island countries in order to provide evidence for formulating public policy in prevention and control of iodine deficiency disorders in these nations.

Evidence-based surgical management of substernal goiter

BACKGROUND

A number of reports have been published concerning the surgical treatment of substernal goiters; however, there is yet to be a comprehensive review of this body of literature using evidence-based methodology.

METHODS

This article is a systematic review of the literature using evidence-based criteria and a review of unpublished data from our institution.

RESULTS

Issue 1. Limited level III/IV data suggest that the incidence of cancer in substernal goiters is not higher than the incidence of cancer in cervical goiters. Risk factors for malignancy in substernal goiters may include a family history of thyroid pathology, a history of cervical radiation therapy, recurrent goiter, and the presence of cervical adenopathy (grade C recommendation). Issue 2. Prospective level V data suggest that, for most patients, expert endocrine surgeons utilize an extracervical approach approximately 2% of the time to remove a substernal goiter safely; a sternotomy or thoracotomy appears more likely in cases of a primary substernal goiter or a mass larger than the thoracic inlet (no recommendation). Issue 3. There may be a higher rate of permanent hypoparathyroidism and unintentional permanent recurrent laryngeal nerve injury when total thyroidectomy is performed for removal of a substernal goiter than for removal of a cervical goiter alone (grade C recommendation). Injury of the external branch of the superior laryngeal nerve was not specifically addressed and is almost certainly underreported. Issue 4. The presence of a substernal goiter, especially being present more than 5 years and causing significant tracheal compression, is likely a risk factor for tracheomalacia and tracheostomy (grade C recommendation). Tracheomalacia with substernal goiter is an infrequent occurrence, and many cases of tracheomalacia can be managed without tracheostomy (no recommendation). Issue 5. Prospective level V data suggest that about 5% to 10% of operations for substernal goiters are performed because of recurrent or persistent disease, although retrospective level V data report an even higher rate, up to 37%. The most common initial operations with recurrence or persistence appear to be subtotal or hemithyroidectomy (no recommendation).

CONCLUSION

Evidence-based recommendations provide reliable information regarding the pathologic findings and operative management of substernal goiters in expert hands.

Risk factors for thyroid cancer: an epidemiological review focused on nutritional factors

OBJECTIVES

The present review summarizes epidemiological evidence on risk factors for thyroid cancer (TC), in particular, nutritional factors.

METHODS

Searches of articles on the issue were conducted using MEDLINE.

RESULTS

Exposure to ionizing radiation, particularly during childhood, is the best-established risk factor for TC. There is also a strong association with history of benign nodules/adenoma or goiter. Iodine deficiency may induce an increasing incidence of benign thyroid conditions, but very high iodine intake also affects thyroid function and, possibly, TC risk. Among dietary factors, fish-the major natural source of iodine in human diet-is not consistently related to TC risk. High intake of cruciferous vegetables shows a weak inverse association with TC. Among other food groups, vegetables other than cruciferous are the only food group showing a favorable effect on TC, with an approximate 20% reduction in risk for subjects with the highest consumption. No effect on TC risk of alcohol, coffee, or other food-groups/nutrients emerged. Height and weight at diagnosis show a moderate positive association with TC risk.

CONCLUSION

At present, the only recognized measures for reducing TC risk is to avoid ionizing radiation and iodine deficiency, particularly in childhood and young women, and to increase vegetable consumption.

Iodine deficiency and its association with intelligence quotient in schoolchildren from Colima, Mexico

Objective

To determine the prevalence of iodine deficiency, its causes and its association with intelligence quotient (IQ) in Mexican schoolchildren.

Design

Cross-sectional analytical study, in which determinations of thyroid gland size, urinary iodine excretion, IQ, iron nutritional status, physical anthropometry, family consumption of goitrogenic foods, type/origin and iodine saturation of salt consumed at home and coliform organisms in drinking water were performed, and the association of each variable with IQ scores was evaluated by multiple regression analyses.

Setting

Municipality of Cuauhtémoc, in Colima, Mexico (altitude: 600–2700 m above sea level). Sea salt is extracted manually nearby and often used for human consumption. Goitre remains present in the region despite over half a century of mandatory salt iodination in the country.

Subjects

Three hundred and three children, similar proportions of boys and girls, mean age 9·3 years, randomly selected from 19 public elementary schools.

Results

Overall goitre rate was 21·4 %; low urinary iodine excretion was found in 19·5 % of the children, high urinary iodine excretion in 32·0 %. IQ scores were transformed into percentile values, with the following categorisation: ≤P5 (low IQ), 48·5 %; >P5 to ≤P25 (below average), 24·2 %; >P25 to <P75 (average), 18·8 %; ≥P75 to <P95 (above average), 3·6 %; ≥P95 (high IQ), 4·9 %. Ninety-two per cent of the population used iodinated salt, but deficient iodine saturation (<50 ppm) was found in 86·8 % of salt samples. The main goitrogenic foods consumed were peanuts (by 31·5 % of the sample), cabbage (30·1 %), broccoli (27·7 %) and cauliflower (25·7 %). Median counts of coliform organisms (colony-forming units/100 ml of drinking water) were: 207·5 (well water), 151 (cisterns), 52 (private homes), 25 (elementary schools) and 12 (kindergartens). Moderate iodine deficiency was associated (P< 0·05) with a 4·26 times higher risk of low IQ.

Conclusions

There is a perturbing negative impact of these findings on human capital acquisition for the region and the country. More attention is needed to ensure effective salt iodination processes, particularly in regions where goitrogens may contribute to the negative effects of iodine deficiency on the intellectual development of children.

Naturally occurring iodine in humic substances in drinking water in Denmark is bioavailable and determines population iodine intake

Iodine intake is important for thyroid function. Iodine content of natural waters is high in some areas and occurs bound in humic substances. Tap water is a major dietary source but bioavailability of organically bound iodine may be impaired. The objective was to assess if naturally occurring iodine bound in humic substances is bioavailable. Tap water was collected at Randers and Skagen waterworks and spot urine samples were collected from 430 long-term Randers and Skagen dwellers, who filled in a questionnaire. Tap water contained 2 μg/l elemental iodine in Randers and 140 μg/l iodine bound in humic substances in Skagen. Median (25; 75 percentile) urinary iodine excretion among Randers and Skagen dwellers not using iodine-containing supplements was 50 (37; 83) μg/24 h and 177 (137; 219) μg/24 h respectively (P < 0·001). The fraction of samples with iodine below 100 μg/24 h was 85·0 % in Randers and 6·5 % in Skagen (P < 0·001). Use of iodine-containing supplements increased urinary iodine by 60 μg/24 h (P < 0·001). This decreased the number of samples with iodine below 100 μg/24 h to 67·3 % and 5·0 % respectively, but increased the number of samples with iodine above 300 μg/24 h to 2·4 % and 16·1 %. Bioavailability of iodine in humic substances in Skagen tap water was about 85 %. Iodine in natural waters may be elemental or found in humic substances. The fraction available suggests an importance of drinking water supply for population iodine intake, although this may not be adequate to estimate population iodine intake.

Etiopathologic Findings of Hyperthyroidism in Cats

None of the studies to date have isolated a single dominant factor that could be incriminated in the development of hyperthyroidism in cats. Rather, most of the studies provide further evidence of the widely held view that hyperthyroidism is a multifactorial disease in this species. At this time, the most likely candidates include one or more of the goitrogenic chemicals that have been shown to be present in cat food or the cat's environment. In addition, mutations of the thyroid stimulating hormone receptor gene or mutations of its associated G proteins seem to play an important role in the pathogenesis of this disease.

The role of diet- and host-related factors in nutrient bioavailability and thus in nutrient-based dietary requirement estimates

To convert physiological requirements into dietary requirements, adjustments are needed for some nutrients that take into account certain diet- and host-related factors specific to a country or region. Nutrients whose requirements should be adjusted in this way include calcium, magnesium, iron, zinc, protein, folate, vitamin A, and carotenoids. The diet-related factors that must be considered depend on the nature of the habitual diet and may include the chemical form of the nutrient and the nature of the dietary matrix, interactions between nutrients and/or organic components, and food preparation and processing practices within the country or region. The host-related factors can be further subdivided into intestinal and systemic factors. Reductions in the secretion of hydrochloric acid, gastric acid, and/or intrinsic factor, together with alterations in the permeability of the intestinal mucosa, are all examples of intestinal factors that can markedly influence the absorption of certain nutrients, but that are often ignored when setting dietary requirements. Systemic factors that should also be considered include nutrient status of the host, age, sex, ethnicity, genotype, and physiological state (e.g., pregnancy or lactation), and chronic and acute infectious disease states. Algorithms can estimate the bioavailability of iron, zinc, protein, folate, vitamin A, and carotenoids, although their accuracy is limited by the complex interactions among the absorption modifiers in the whole diet. For calcium and magnesium, the amount available for absorption is still estimated from their major food sources in the habitual diet. Currently, there are often large differences in the adjustments employed to convert physiological requirements to dietary requirements, even among countries consuming diets of similar patterns.

Time trends and geographic variations for thyroid cancer in New Caledonia, a very high incidence area (1985-1999)

Thyroid cancer incidence in New Caledonia is the highest reported in the world and is approximately 10-fold higher than in most developed countries. We describe the incidence patterns in this country according to histological and sociodemographic characteristics to give clues about potential etiologic factors. Another objective is to see whether the incidence figures are related to enhanced detection of small size carcinomas. The study included all 498 cases of thyroid cancer diagnosed in 1985-1999. Pathology reports were systematically reviewed to determine the histological type of the tumor and the size of the cancerous nodules. The incidence of carcinomas < or =10 mm was taken as an indicator of enhanced detection due to improved screening procedures. The age-standardized incidence rates in 1985-1999 were exceptionally high in Melanesian women (71.4/100,000) and men (10.4/100,000). The incidence increased three-fold in women from 1995 onwards. The increase in incidence was more striking for papillary carcinomas < or =10 mm than for large size carcinomas, but an increased incidence of carcinomas >10 mm was also observed among women. The analysis by municipality of residence in Melanesian women showed that the incidence was twice as high in 1995-1999 in the Loyalty Islands as in the rest of the country. The sharp increase of thyroid cancer incidence in 1985-1999 in New Caledonia was partly related to enhanced detection of small size carcinomas. The elevated incidence of thyroid cancers, as well as the ethnic and geographic disparities, may result from common environmental or lifestyle risk factors that need to be identified.

Improving the bioavailability of nutrients in plant foods at the household level

Plant foods are the major staples of diets in developing countries, in which the consumption of animal-source foods is often low because of economic and/or religious concerns. However, such plant-based diets are often associated with micronutrient deficits, exacerbated in part by poor micronutrient bioavailability. Diet-related factors in plant foods that affect bioavailability include: the chemical form of the nutrient in food and/or nature of the food matrix; interactions between nutrients and other organic components (e.g. phytate, polyphenols, dietary fibre, oxalic acid, protein, fat, ascorbic acid); pretreatment of food as a result of processing and/or preparation practices. Consequently, household strategies that reduce the content or counteract the inhibiting effects of these factors on micronutrient bioavailability are urgently needed in developing-country settings. Examples of such strategies include: germination, microbial fermentation or soaking to reduce the phytate and polyphenol content of unrefined cereal porridges used for young child feeding; addition of ascorbic acid-containing fruits to enhance non-haem-Fe absorption; heating to destroy heat-labile anti-nutritional factors (e.g. goitrogens, thiaminases) or disrupt carotenoid-protein complexes. Such strategies have been employed in both experimental isotope-absorption and community-based studies. Increases in Fe, Zn and Ca absorption have been reported in adults fed dephytinized cereals compared with cereals containing their native phytate. In community-based studies in rural Malawi improvements in dietary quality and arm-muscle area and reductions in the incidence of anaemia and common infections in young children have been observed.

Self-reported goiter is associated with a significantly increased risk of gastric noncardia adenocarcinoma in a large population-based Chinese cohort

Iodine is concentrated by the gastric mucosa, where it may act as an antioxidant. Therefore, iodine deficiency, and its sequelae goiter, may be associated with an increased risk of gastric cancer. We examined the association between self-reported goiter and upper gastrointestinal cancer in a Chinese cohort of 29,584 adults. Using multivariate adjusted Cox models, we found goiter associated with a significantly increased risk of gastric noncardia adenocarcinoma, HR (95% CI) 2.04 (1.01, 4.11) and nonsignificantly with gastric cardia adenocarcinoma, HR (95% CI) 1.45 (0.91, 2.30). We also found a borderline, insignificant increased risk of esophageal squamous cell carcinoma, HR (95% CI) 1.37 (0.97, 1.94). Our findings are consistent with the hypothesis that iodine deficiency is associated with an increased risk of gastric cancer.

Epidemiologic study of relationships between consumption of commercial canned food and risk of hyperthyroidism in cats

OBJECTIVE

To determine whether the increasing prevalence of feline hyperthyroidism is the result of aging of the cat population and whether consumption of canned foods at various times throughout life is associated with increased risk of hyperthyroidism.

DESIGN

Retrospective and case-control studies.

STUDY POPULATION

Medical records of 169,576 cats, including 3,570 cats with hyperthyroidism, evaluated at 9 veterinary school hospitals during a 20-year period, and 109 cats with hyperthyroidism (cases) and 173 cats without hyperthyroidism (controls).

PROCEDURE

Age-adjusted hospital prevalence of hyperthyroidism was calculated by use of Veterinary Medical Database records. On the basis of owners' questionnaire responses, logistic regression was used to evaluate associations between consumption of canned food and development of hyperthyroidism.

RESULTS

Age-specific hospital prevalence of feline hyperthyroidism increased significantly from 1978 to 1997. Overall, consumption of pop-top canned (vs dry) food at various times throughout life and each additional year of age were associated with greater risk of developing hyperthyroidism. In female cats, increased risk was associated with consumption of food packaged in pop-top cans or in combinations of pop-top and non-pop-top cans. In male cats, increased risk was associated with consumption of food packaged in pop-top cans and age.

CONCLUSIONS AND CLINICAL RELEVANCE

These findings suggest that the increasing prevalence of feline hyperthyroidism is not solely the result of aging of the cat population and that canned foods may play a role.

Dynamics of the iodine-goitrogen balance in the thyroid status of catfish from selected fresh and brackish water bodies

The study was designed to investigate the dynamics of the goitrogen-iodine balance in Igbokoda brackish and Ogbese fresh water bodies in Ondo State, Nigeria. The parameters determined include iodine, thiocyanate, chloride, nitrate, calcium, magnesium hardness, calcium hardness, total hardness, and total coliform counts in water, sediment and/or fish (flesh and serum). The fish were subjected to a number of treatments (boiling with water or sodium chloride solution, frying or roasting) prior to analysis. The iodine level (microg I/100g) in the flesh of fish varied with size, treatment and location; it increased with size, was reduced by some treatments (boiling with either water or NaCl solution), while frying and roasting did not affect the level. The least values were 93.45 (Ogbese fish boiled with NaCl solution) and 160.94 (Igbokoda fish boiled with either water or NaCl solution). On the whole, Igbokoda (160.94-314.08) had higher values than Ogbese (93.45-205.06). Serum iodine (microg I/100mL) was equally higher in Igbokoda (5.00-9.00) compared to Ogbese (2.80-5.00). Only the large sized fish of Ogbese recorded a value of 5.00 micromol/L for thiocyanate while this parameter was not detected in other samples. The calculated I/goitrogen ratios (I/Ca, I/NO3, I/Cl and I/SCN) were higher for Igbokoda water than Ogbese water with the exception of I/Mg. This was equally reinforced by the total count of coliforms (goitrogenic), which was higher in Ogbese (3.0 x 10(3)) than in Igbokoda (2.7 x 10(3)). These results indicate that the Igbokoda brackish water body would be a better source of iodine than Ogbese fresh water body for the population dependent on them.

Humic substances in drinking water and the epidemiology of thyroid disease

Thyroid diseases are common in all populations but the type and frequency depends on environmental factors. In Denmark geographical differences in iodine intake are caused by different iodine contents of drinking water, which varies from < 1 to 139 microg iodine per litre. Comparative epidemiologic studies have demonstrated considerable differences in type and occurrence of thyroid disease with more goitre and hyperthyroidism in Aalborg with water iodine content around 5 microg/L, and more hypothyroidism in Copenhagen with water iodine around 20 microg/L. In Denmark, iodine in ground water is bound in humic substances, which have probably leached from marine sediments in the aquifers. Interestingly, humic substances in water from other parts of the world have goitrogenic properties, especially humic substances from coal and shale. Humic substances are heterogeneous mixtures of naturally occurring molecules, produced by decomposition of plant and animal tissues. The effect of humic substances in drinking water on the epidemiology of thyroid disease probably depends on the source of aquifer sediments.

Ultrasonographic determination of goiter prevalence in southern Brazilian schoolchildren

The aim of the present study was to estimate the prevalence of goiter in schoolchildren in a formerly iodine-deficient region in southern Brazil by assessing the relationship between body surface area (m2 ) and thyroid volume (ml) measured by ultrasonography. A population-based sample of 1,094 randomly selected schoolchildren (6 to 14 years; 556 boys and 538 girls) underwent clinical evaluation. A total of 119 (10.9%) children were diagnosed with goiter upon clinical examination according to WHO criteria (grade Ia: 65, grade Ib: 24, grade II: 29, grade III: 1). Of these, 85 underwent ultrasonography. In order to ascertain the absence of goiter in the 975 schoolchildren with a negative result upon clinical examination, one of ten children was randomly selected for ultrasonography. Sixty-two children agreed to be submitted to the exam. Thus, 147 schoolchildren were evaluated by ultrasonography (7.5-MHz transducer). Goiter was considered to be present when the thyroid volume:body surface area index was >6.2 ml/m . The estimated prevalence of goiter if all schoolchildren had been submitted to thyroid volume measurement by ultrasound was 7.2%; it was higher in the lower socioeconomic class (8.2%) than in the upper (7.8%) and middle classes (6.5%). In conclusion, the prevalence of goiter in schoolchildren of this region was higher than in other iodine-sufficient areas, especially in lower socioeconomic classes. Goiter in this region may be associated with naturally occurring goitrogens that operate more intensively among less privileged individuals.

Risk factors for goiter and thyroid nodules

The occurrence of thyroid diseases is determined by interplay between genetic and environmental factors. The major environmental factor that determines goiter prevalence is iodine status, but other environmental factors influencing entire populations have been identified such as goitrogens in food and drinking water. Less focus has been on individual environmental factors and the interplay between factors. The goiter prevalence is higher in certain groups in the population. The variation in goiter prevalence between the genders is well known with a higher occurrence among women. The association with age is probably dependent on iodine status, because it seems that the zenith of goiter prevalence appears earlier in life the more severe iodine deficiency the population is exposed to. The association with individual risk factors has been investigated in some studies, especially the association with tobacco smoking. In iodine-deficient areas, a strong association between tobacco smoking and goiter prevalence is found, whereas the association is less pronounced in iodine-replete areas. This was predictable from experimental studies showing thiocyanate to be the mediator of the goitrogenic effect of tobacco smoke acting as a competitive inhibitor of iodine uptake. The association with alcohol intake has only been investigated in few studies, but a low occurrence of goiter among alcohol consumers has been found. The mechanism of this association is not known. Increased goiter prevalence during pregnancy has been reported, and recently a long-term goitrogenic effect of pregnancies has also been shown. As demonstrated for tobacco smoking, this association is dependent on iodine status, because the association has only been found in areas with a suboptimal iodine intake. This indicates pregnancy-induced goiter to be the result of exacerbation of existing iodine deficiency. Recently, the use of oral contraceptives has been shown to be associated with a markedly reduced prevalence of goiter, although experimental studies have previously shown proliferative effects of estrogens on thyrocytes. Some implications for prevention of thyroid disease could be suggested. Discussion of smoking habits should be included in a consultation for goiter with a motivation to quit smoking. Iodine deficiency has particularly strong goitrogenic effects during pregnancy and for the sake of the mother as well as the fetus, sufficient iodine supply should be ensured to all pregnant women. The difference in age maximum in goiter prevalence suggests that monitoring of iodine deficiency disorders should ideally include a spectrum of age groups.

Toxicology review and risk assessment of resorcinol: thyroid effects

Resorcinol administered at high doses to rodents can disrupt thyroid hormone synthesis and can produce goitrogenic effects. These effects were not seen in a 2-year bioassay at doses of up to 520 mg/kg/day. There are species-specific differences in synthesis, binding, and transport of thyroid hormone that complicate interpretation of goitrogenesis in rodents. Clinical case reports from patients undergoing resorcinol therapy for dermatological indications reveal thyroid side effects when copious amounts of resorcinol-containing ointments are applied to integrity-compromised skin for months to years. Effect levels were greater than 34 mg/kg/day. Occupational epidemiology studies provide no evidence that exposure to resorcinol at levels greater than found in the general environment causes thyroid dysfunction. Studies investigating the relationship between endemic goiter and exposure to "phenolics," including resorcinol, in drinking water do not fulfill accepted scientific criteria for establishing resorcinol as a cause of thyroid disease. Those reports neither quantify exposure levels nor demonstrate dose-response relationships or rule out confounding by the multiple other chemicals present in water supplies, by bacterial contamination of water, or by nutritional factors. A risk assessment comparing potential worst-case exposures to resorcinol through its use in dermatological preparations supports the conclusion that under real-world conditions, human exposures to resorcinol are not expected to cause adverse effects on thyroid function.

Interpretation of thyroid function tests

The introduction of sensitive thyrotropin assays and free thyroid hormone measurements has simplified the interpretation of thyroid function tests. However, important pitfalls and difficult cases still exist. In this review, thyroid function test results are grouped into six different patterns. We propose that if assays for thyrotropin, free T3, and free T4 are all done, knowledge of these patterns coupled with clinical details and simple additional tests allow a diagnosis to be made in almost all cases.

Pathogenesis of thyroid nodules: histological classification?

Thyroid nodule genesis may be considered as an amplification of thyroid heterogeneity due to genetic and/or epigenetic mechanisms. We classified the thyroid nodules in five types with distinct histological features: hyperplastic, neoplastic, colloid, cystic and thyroiditic nodules. Hyperplastic: Thyrocyte proliferation is under the control of TSH but several other paracrine and autocrine factors are secreted by follicular cells, the stromal apparatus and the lymphocytes, which are implicated in initiation and perpetuation of thyroid hyperplasia. Growth occurs mainly through TSHR, cAMP and PKA. Constitutive cAMP overproduction has been shown to be due to point mutation of the TSHR or Gs protein, producing overgrowth and hyperfunction. Neoplastic: Several activated oncogenes have been identified in thyroid malignancies. Oncogenes relevant to the thyroid carcinogenesis are: mutated TSHR and gsp (constitutive activation of cAMP); TRK (receptor for NGF); RET/PTC (phosphorylation of tyrosine kinase receptor)--an isoform of this oncogene is induced by radiation: ras (it encodes Gs proteins transducing mitogenic signals); and c-MET (receptor for hepatocyte growth factor). The evolution of a differentiated thyroid cancer towards an undifferentiated cancer is due to a mutation of a family of proteins (i.e., p53), which acts as a brake, preventing the genomic instability of cancer. It is suggested that a tumor initiates by RET or ras and possibly progresses--as a result of additional mutations and by p53 mutation--to anaplastic carcinoma. Colloid: Flattening of the epithelium and dilatation of follicles containing viscous material--made up by a concentrated solution of thyroglobulin (hTg)--is the characteristic of the colloid nodule. A defect of intraluminal reabsorption of hTg has been suggested but not proven. Experimentally, a load of iodine is able to change thyroid hyperplasia to a colloid feature; however, a load of iodine is rarely found in the clinical history of patients. A new clue to the pathogenesis comes from the finding that a relevant part of the colloid (10-20%) is made up of insoluble globules, where hTg is compacted in a polymeric form. It is suggested that stocking hTg into globules is defective in colloid nodules, leading to enormous enlargement of the follicle. Cystic: It is estimated that between 15 and 40% of thyroid nodules are partly or entirely cystic. The 'true cyst' is rare; most of the so-called cystic nodules are 'pseudocysts', which follow necrosis and colliquation. Necrosis issues as an imbalance between growth and the precisely regulated process of angiogenesis. More recently, the VEGF/VPF has been found to be at the origin of recent and recurrent cysts. Immunotoxic and apoptotic mechanisms have also been suggested. Chemical analysis of cystic fluid showed a 'denatured' and 'serum-like' pattern suggesting different mechanisms in the pathogenesis of the pseudocystic thyroid nodules. Thyroiditic: Nodular lymphocytic thyroiditis (NLT) includes two different entities: 1) lymphocyte thyroiditis growing as a nodule in a hyperplastic or normal gland, and 2) lymphocyte thyroiditis associated in the same nodule with other nodular diseases of the thyroid: papillary thyroid carcinoma and lymphoma have been found to be associated to chronic lymphocytic thyroiditis.

Histomorphometry and quantification of nucleolar organizer regions in bovine thyroid containing methylthiouracil residues

In order to study the morphology and morphometry and to characterize and quantify the nucleolar organizer regions (NORs) of bovine thyroids containing methylthiouracil (MTU) residues, five animals were orally treated with a suspension of MTU (5 g/animal/day) for 20 days (group A). This treatment protocol was interrupted 5 days before the the animals were slaughtered. Six animals receiving placebos composed group B. A third group (group C) was composed of normal thyroids obtained from a slaughterhouse. All glands were previously assessed for detection of antithyroid residues by chromatography, and only those glands from MTU-treated animals were positive. Follicles of glands from group A showed wide variation in size and shape. There was a predominance of small follicles covered by multiple layers of columnar cells, sometimes forming papillary projections into the lumen, characterizing severe interfollicular and intrafollicular adenomatosis. Many follicles had vacuolated cells with nuclei showing karyolysis or pyknosis and reduced amounts of a low-density and very excavated colloid. They also showed higher follicular epithelia and larger proportions of their structural components when compared with glands of groups B and C. In the thyroids from group A, the argyrophilic nucleolar organizer region-associated proteins (AgNORs) were greater in number, with small ones scattered all over the nucleus. Although the size of AgNORs in thyroids from groups B and C was variable, these AgNORs were fewer and larger than were those in glands from group A. In conclusion, the MTU induces proliferation and regressive changes in follicular cells, and the AgNOR technique is efficient to distinguish different degrees of thyroid hyperplasia.

Atypical Thyroiditis in Huelva, Spain

OBJECTIVE

To report an epidemic of atypical thyroiditis that occurred in southwestern Europe during 1995.

METHODS

We present the clinical, laboratory, morphologic, and histologic features of 672 cases of thyroiditis and describe the results of treatment.

RESULTS

During 1995, atypical thyroiditis was diagnosed in 672 of 725 patients with thyroid disorders encountered at our medical center in Huelva, Spain. Of these patients, 98% were women with normal ovarian function. The clinical findings were acute or subacute manifestation of diffuse nodular enlargement of the thyroid and spontaneous, severe pain on deglutition and palpation of the gland. Initial hematology and serum biochemistry studies, free triiodothyronine, free thyroxine, thyrotropin, and thyroid-stimulating immunoglobulins were in the normal range, but after the second week, the thyrotropin level began to increase. Thyroid antibodies (thyroglobulin and thyroid peroxidase) increased up to 300 times the high-normal level. Ultrasonography exhibited diffuse nodular enlargement of the thyroid gland, with irregular hypoechoic, normal, and hyperechoic zones. Fine-needle aspiration biopsy showed abundant lymphocytic infiltration. The best treatment results were obtained with the combination of levothyroxine and deflazacort. Because the epidemic appeared after a severe drought of 5-year duration (1991 to 1995) and affected women with normal ovarian function, our etiopathogenetic hypothesis was that an estrogen-like chemical substance polluted the area swamps. The high concentration of the pollutant was attributable to diminished water levels (8% of their capacity at the end of the drought period), and this situation may have affected the population through tap water used for human consumption.

CONCLUSION

We describe an atypical autoimmune thyroiditis that affected primarily women of reproductive age, after a severe drought. The main features were a very painful, diffuse nodular enlargement of the thyroid gland, substantially increased thyroid antibodies, good response to levothyroxine and deflazacort combination treatment, and a benign evolution to chronic thyroiditis. Pollutants from various sources should be considered when atypical thyroiditis occurs in any community.

Severe Gestational Hypothyroidism Increases BBB Nutrient Transport in the Offspring

Brain growth spurt and development is highly influenced by thyroid hormones. We reported earlier that chronic maternal potassium thiocyanate feeding (induced moderate hypothyroidism) resulted in reversible decrease in Blood-Brain Barrier (BBB) glucose transport in the offspring. To assess whether severe hypothyroidism as often seen in endemic areas would have greater effect, we have now determined the thyroid status and BBB nutrient transport in the pups born to dams made severely hypothyroid by feeding 6-n-propyl thiouracil (PTU), the potent antithyroid compound. The pups of PTU fed dams had lower birth weights (P < 0.001) than controls. Their weanling body weight and brain weight were also significantly lower. They were very severely hypothyroid (serum T4 < 0.7 μg/d1 and T3 < 0.5 ng/ml) and surprisingly there was a significant increase in the BBB transport of all three nutrients tested (leucine, tyrosine and 2-deoxy-D-glucose). The increased BBB nutrient transport however does not appear to be due to opening/breakdown of BBB as evident from the lack of extravasation of Evans blue injected into the carotid artery. Interestingly, T3 supplementation to the dams and offspring, could mitigate the changes not only in BBB nutrient transport but also their body and brain weights at weanling.

Environmental endocrine modulators and human health: an assessment of the biological evidence

Recently, a great deal of attention and interest has been directed toward the hypothesis that exposure, particularly in utero exposure, to certain environmental chemicals might be capable of causing a spectrum of adverse effects as a result of endocrine modulation. In particular, the hypothesis has focused on the idea that certain organochlorine and other compounds acting as weak estrogens have the capability, either alone or in combination, to produce a variety of adverse effects, including breast, testicular and prostate cancer, adverse effects on male reproductive tract, endometriosis, fertility problems, alterations of sexual behavior, learning disability or delay, and adverse effects on immune and thyroid function. While hormones are potent modulators of biochemical and physiological function, the implication that exposure to environmental hormones (e.g., xenoestrogens) has this capability is uncertain. While it is reasonable to hypothesize that exposure to estrogen-like compounds, whatever their source, could adversely affect human health, biological plausibility alone is an insufficient basis for concluding that environmental endocrine modulators have adversely affected humans. Diethylstilbestrol (DES) is a potent, synthetic estrogen administered under a variety of dosing protocols to millions of women in the belief (now known to be mistaken) that it would prevent miscarriage. As a result of this use, substantial in utero exposure to large numbers of male and female offspring occurred. Numerous studies have been conducted on the health consequences of in utero DES exposure among the adult offspring of these women. There are also extensive animal data on the effects of DES and there is a high degree of concordance between effects observed in animals and humans. The extensive human data in DES-exposed cohorts provide a useful basis for assessing the biological plausibility that potential adverse effects might occur following in utero exposure to compounds identified as environmental estrogens. The effects observed in both animals and humans following in utero exposure to sufficient doses of DES are consistent with basic principles of dose response as well as the possibility of maternal dose levels below which potential non-cancer effects may not occur. Significant differences in estrogenic potency between DES and chemicals identified to date as environmental estrogens, as well as an even larger number of naturally occurring dietary phytoestrogens, must be taken into account when inferring potential effects from in utero exposure to any of these substances. The antiestrogenic properties of many of these same exogenous compounds might also diminish net estrogenic effects. Based on the extensive data on DES-exposed cohorts, it appears unlikely that in utero exposure to usual levels of environmental estrogenic substances, from whatever source, would be sufficient to produce many of the effects (i.e., endometriosis, adverse effects on the male reproductive tract, male and female fertility problems, alterations of sexual behavior, learning problems, immune system effects or thyroid effects) hypothesized as potentially resulting from exposure to chemicals identified to date as environmental estrogens.

Anti-thyroid isoflavones from soybean: isolation, characterization, and mechanisms of action

The soybean has been implicated in diet-induced goiter by many studies. The extensive consumption of soy products in infant formulas and in vegetarian diets makes it essential to define the goitrogenic potential. In this report, it was observed that an acidic methanolic extract of soybeans contains compounds that inhibit thyroid peroxidase- (TPO) catalyzed reactions essential to thyroid hormone synthesis. Analysis of the soybean extract using HPLC, UV-VIS spectrophotometry, and LC-MS led to identification of the isoflavones genistein and daidzein as major components by direct comparison with authentic standard reference isoflavones. HPLC fractionation and enzymatic assay of the soybean extract showed that the components responsible for inhibition of TPO-catalyzed reactions coeluted with daidzein and genistein. In the presence of iodide ion, genistein and daidzein blocked TPO-catalyzed tyrosine iodination by acting as alternate substrates, yielding mono-, di-, and triiodoisoflavones. Genistein also inhibited thyroxine synthesis using iodinated casein or human goiter thyroglobulin as substrates for the coupling reaction. Incubation of either isoflavone with TPO in the presence of H2O2 caused irreversible inactivation of the enzyme; however, the presence of iodide ion in the incubations completely abolished the inactivation. The IC50 values for inhibition of TPO-catalyzed reactions by genistein and daidzein were ca. 1-10 microM, concentrations that approach the total isoflavone levels (ca. 1 microM) previously measured in plasma from humans consuming soy products. Because inhibition of thyroid hormone synthesis can induce goiter and thyroid neoplasia in rodents, delineation of anti-thyroid mechanisms for soy isoflavones may be important for extrapolating goitrogenic hazards identified in chronic rodent bioassays to humans consuming soy products.

Thyroid homeostasis and retinol circulating complex relationships in a severe iodine-deficient area of Senegal

In adult subjects living in a severely iodine-deficient area (median urinary iodine 10 microgram/L), we evaluated the biochemical parameters of protein malnutrition in relation to thyroid homeostasis. Serum transthyretine (TTR), retinol binding protein (RBP) and retinol, all components of the retinol circulating complex (RCC), as well as ceruloplasmin levels, were determined in 63 subjects (44 F/19 M). These comprised 21 controls, 31 who were euthyroid with goiter WHO stage 2 or 3 and 11 who met the criteria of hypothyroidism (i.e. FT4 < 8 pmol/L and TSH > 4.13 mU/L) with goiter stage no more than 1b. No differences in the values of TTR and RBP were found between males and females, whereas the retinol values were slightly higher in males. The mean retinol binding protein values were lower than the normal range in all three groups but were significantly lower (p < 0.01; < 0.05) in hypothyroid subjects than in the other two groups. All hypothyroid subjects exhibited reduced retinol binding protein levels and 1/3 of them showed a marked decrease. The circulating levels of transthyretine were also lower than the normal range for western countries. 45% of the hypothyroid, 26% of goitrous and 9% of control subjects exhibited a transthyretine lower than 12 mg/dl, but the mean values were not dissimilar. The mean retinol values were within the normal range in all three groups but were lower in hypothyroid as compared to the controls (< 0.01). The resulting retinol/RBP ratio was over 1 in both the whole sample and in the subgroups. Ceruloplasmin levels were in the normal range in all groups. The data indicated that hypothyroid subjects had reduced retinol binding protein and retinol circulating complex network compared to euthyroid subjects.

Management of patients with substernal goiters

The presence of a substernal goiter is an indication for thyroidectomy, even in asymptomatic patients, because there is no other effective method of preventing growth of the goiter. Both primary and secondary substernal goiters usually exhibit slow but steady growth, which leads to tracheal, esophageal, vascular, and neurologic compression syndromes. Airway obstruction, which poses a life-threatening situation, may be suddenly precipitated by spontaneous or traumatically induced bleeding into the substernal goiter, as well as by tracheal infections. Substernal goiters can also produce symptoms of thyrotoxicosis. In addition, substernal goiters are known to have a relatively high incidence of malignancy. CT scans permit proper distinction between primary and secondary goiters and allow for sound preoperative planning. Advances in anesthetic techniques and the use of small-caliber endotracheal tubes facilitate proper perioperative management, even for patients with significant respiratory compression symptoms. A tracheostomy is rarely necessary. Aggressive surgical therapy for substernal goiters avoids life-threatening situations and results in minimal morbidity and practically zero mortality when performed by a surgeon experienced in managing such patients. Resection of substernal goiters generally can be accomplished through a transcervical approach, either by digital mobilization alone or with the addition of a spoon technique. Morcellization or fragmentation of the goiter is less desirable because of the possibility of dissemination of potential malignancies within the goiter. Primary intrathoracic goiters, recurrent goiters, and malignant goiters often require a median sternotomy for safe removal. The recurrence rate of goiters after surgical removal is low.

Endemic goiter in Calabria: etiopathogenesis and thyroid function

An endemic goiter study was carried out in a vast territory of the Calabria region, including the provinces of Catanzaro and Cosenza. About 50% of 7231 school-children, aged between 6 and 12 years, examined in 34 villages, presented a thyroid enlargement. The high prevalence of goiter seems to be related to a moderate iodine deficiency intake indicated by a mild urinary iodine excretion (lower than 100 micrograms/g creatinine). In a few villages, in which a two year voluntary iodine prophylaxis was carried out, an increase in the urinary iodine excretion with a decreased goiter prevalence was observed. A slight increase in TT3, FT3 and TSH in one endemic area studied, compared to the control area, was also observed. These data suggest that an effective program of iodoprophylaxis is fundamental in this region as well.

Antithyroid and goitrogenic effects of coal-water extracts from iodine-sufficient goiter areas

Goiter in iodine-sufficient areas has been linked to water-borne goitrogens in watersheds and aquifers rich in coal and shale. In the present study, the potential antithyroid and goitrogenic effects of coal-water extracts (CWE) were investigated in vivo in rats after chronic and acute oral administration of CWE, and in vitro by a thyroid peroxidase (TPO) enzyme system. CWE was prepared by continuous extraction of ground (40 mesh) Appalachian coal with goitrogen-free water (GFW). Female Buffalo rats fed on Purina iodine-rich diet (12 micrograms I-/day/rat), were given ad lib CWE (50 mg/ml; approximately 20 mL/day/rat) or GFW (controls) for 2 months. At the end of the experiment, 125I 1 microCi, was injected i.p. and 4 h later the thyroid glands were removed, weighed, and analyzed histologically and for total 125I and 125I-labeled compounds. Rats on CWE had larger thyroid glands [7.2 +/- 0.3 mg/100 g (mean +/- SE) vs 5.0 +/- 0.5 controls; p < 0.005] with distinct histological changes of smaller thyroid follicles, some with columnar epithelium, and with more dense colloid than in controls, and had significant inhibition of the coupling mechanism for production of thyroid hormones [125MIT + DIT/125T3 + T4: 5.1 +/- 0.2 vs 3.9 +/- 0.1 controls, p < 0.005; and 125T3 + T4 (%): 10.6 +/- 0.3 vs 12.6 +/- 0.4 controls, p < 0.005]. Female Sprague-Dawley rats under the same conditions as Buffalo rats were given acutely by GI tube 2 mL of CWE (5 g/mL) or GFW (controls).(ABSTRACT TRUNCATED AT 250 WORDS)

Antithyroid effects of coal-derived pollutants

Endemic goiter in iodide-sufficient areas of the United States and Colombia has been linked to watersheds rich in coal and shale, which several reports suggest are the source of water-borne goitrogens. In this report the potential antithyroid activities of aqueous coal and shale extracts and of compounds identified in aqueous effluents from coal conversion processes were assayed in thyroid peroxidase (TPO) and thyroid slice systems. Aqueous extracts of coal and black shale were potent inhibitors of TPO or 125I organification by thyroid slices. The most abundant water-soluble compounds derived from coal are dihydroxy-phenols, thiocyanate, disulfides, and hydroxypyridines. The dihydroxyphenols resorcinol, 2-methylresorcinol, and 5-methylresorcinol (orcinol) were 26.7, 22.5, and 7.2 times more potent, respectively, than the antithyroid drug 6-propylthiouracil (PTU). Other dihydroxyphenols and thiocyanate were less potent but comparable in activity to PTU. All dihydroxypyridines and 3-hydroxypyridine produced inhibitory effects comparable to PTU. None of the disulfides inhibited TPO. The antiperoxidase effects of combinations of two dihydroxyphenols or one dihydroxyphenol and SCN were additive, whereas the effects of a combination of four dihydroxyphenols at threshold inhibitory concentrations were synergistic, resulting in net effects equivalent to or greater than the sum of the individual effects. Thus, antithyroid effects may be greatly amplified by exposure to multiple coal-derived goitrogens and could be many times that produced by any one of the contributing pollutants. These results demonstrate that potent water-borne goitrogens are derived from coal and shale and that their contamination of water supplies could pose a serious threat of thyroid disorders.

Epidemiology of iodine deficiency

Iodine deficiency (ID) causes goiter, cretinism, neonatal hypothyroidism, irreversible mental retardation, and child and infant death. Over one billion people are at risk, most of them in developing countries. While ID is the primordial factor in these conditions, other environmental and host factors significantly modify the magnitude and clinical presentation of iodine deficiency disorders. The interactions and mechanisms by which these factors operate are complex and mostly unknown, requiring more investigation.

Endemic goiter and endemic thyroid disorders

The primary role of iodine deficiency in goitrogenesis and the prevention and treatment of endemic goiter by iodine supplementation is firmly established. Unfortunately, implementation of iodine prophylaxis programs has met with considerable technical and socioeconomic difficulties. Besides, lack of knowledge concerning some of the other causative factors of endemic goiter has prevented development of appropriate measures for its complete eradication in those areas where goiter persists in spite of prolonged and adequate iodine supplementation. At present, no less than 5% of the world's population have goiters and associated disorders, resulting in a public health and socioeconomic problem of major proportions. Seventy-five percent of people with goiter live in less developed countries where iodine deficiency is prevalent. Goiter prevalence rates of more than 50% and the highest frequency of severe cases of iodine deficiency disorders, namely, cretinism, congenital hypothyroidism, and various degrees of impairment of growth and mental development are found in endemic areas with extreme iodine deficiency. Goiters are usually multinodular and of very large size, producing, on occasion, signs of compression that require surgery. Recurrence rates are as high as 25-30% and second surgery accounts for 16% of all thyroidectomies. Unfortunately, most of these goiters occur in areas with highly restricted medical and surgical facilities. Twenty-five percent of people with goiters live in more developed countries where goiter continues to occur in certain areas despite iodine prophylaxis. Iodine-sufficient goiters are associated with autoimmune thyroiditis, hypothyroidism, hyperthyroidism, and thyroid carcinoma. Goiter is of considerable surgical significance in iodine-sufficient endemic areas and, to a lesser degree, in nonendemic areas where it is called "sporadic" goiter. Recurrence rates of iodine-sufficient goiter are 10-19% following thyroidectomy. Since most of these goiters grow by mechanisms other than increased thyrotropin (TSH) stimulation, treatment with suppressive doses of L-thyroxine is inefficient and, because of possible complications, not recommended. Although Graves' hyperthyroidism is not directly related to endemic goiter, it does relate adversely with ingestion or administration of iodine. At present, Graves' disease is treated with 131I or antithyroid drugs in more than 90% of the cases. The incidence rates of papillary, follicular, and anaplastic thyroid carcinomas appear to be related to endemic goiter and iodine supplementation, with surgery being required in essentially all of these cases.