Thyroid Surgery as Affected by the Generalized Use of Iodized Salt in an Endemic Goitre Region-Preventive Surgery

The Prevention of Iodine Deficiency: A History

Iodine is an essential component of the hormones produced by the thyroid gland and is, therefore, essential for mammalian life. A landmark trial in the early 20th century definitively demonstrated that iodine supplementation could prevent what was then known as "endemic goiter." Subsequent studies over the next decades demonstrated that iodine deficiency causes a spectrum of disease, including not just goiter, but also cretinism, intellectual impairment, and adverse obstetric outcomes. Salt iodization, first used in Switzerland and the United States in the1920s, has become the mainstay of iodine deficiency prevention efforts. The dramatic reduction in the global prevalence of iodine deficiency disorders (IDD) over the past 30 years represents an outstanding and under-recognized public health achievement. This narrative review provides an overview of critical scientific discoveries and advances in public health nutrition related to the prevention of IDD in the United States and worldwide. This review was written to commemorate the centennial of the founding of the American Thyroid Association.

The Cognitive Effects of Micronutrient Deficiency: Evidence from Salt Iodization in the United States

Iodine deficiency is the leading cause of preventable mental retardation in the world today. The condition, which was common in the developed world until the introduction of iodized salt in the 1920s, is connected to low iodine levels in the soil and water. We examine the impact of salt iodization on cognitive outcomes in the US by taking advantage of this natural geographic variation. Salt was iodized over a short period of time beginning in 1924. We use military data collected during WWI and WWII to compare outcomes of cohorts born before and after iodization in localities that were naturally poor and rich in iodine. We find that for the one quarter of the population most deficient in iodine this intervention raised IQ by approximately one standard deviation. Our results can explain roughly one decade's worth of the upward trend in IQ in the US (the Flynn Effect). We also document a large increase in thyroid-related deaths following the countrywide adoption of iodized salt, which affected mostly older individuals in localities with high prevalence of iodine deficiency.

Studies on Endemic and Experimental Goitre

1. 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.

Reappraisal of the risk of iodine-induced hyperthyroidism: an epidemiological population survey

The occurrence of iodine-induced hyperthyroidism (IIH) has been reported after iodine supplementation from clinics and hospitals, but not following an epidemiologic survey. We studied the prevalence of thyroid derangement in a population following iodine supplementation. One yr after more than 75% of the population had been consuming 40 ppm iodized salt; information regarding history of endemic goiter and iodized salt production, distribution, consumption and monitoring were collected in four cities of the Islamic Republic of Iran. A total of 6048 subjects were randomly selected. All subjects were assessed for size of goiter, and urinary iodine and serum T4, T3, TSH, anti-thyroglobulin and anti-thyroperoxide were measured. Before iodine supplementation, all four cities were areas of endemic goiter. The rate of household consumption of iodized salt was 50, 75 and 90% in 1994, 1995 and 1996, respectively. Ninety-one percent of the salt samples contained 15-55 ppm iodide. Total goiter rate was 57, 62 and 68%; median urinary iodine was 188, 197 and 190 microg/l in the age groups of 6-18, 19-40 and >40 yr, respectively. Prevalence of clinical and subclinical hyperthyroidism was 0.34 and 0.41 and those of clinical and subclinical hypothyroidism were 0.51 and 1.07%, respectively. Nine point eight and 18% in the 19-40 yr age group and 17.6 and 25.6% in >40 yr old subjects had positive anti-thyroperoxidase and anti-thyroglobulin, respectively. This systemic epidemiologic study in an iodine deficient population showed that, following a well-executed iodine supplementation program, the occurrence of IIH is rare.

Iodine-induced hyperthyroidism due to nonionic contrast radiography in the elderly

PURPOSE

To identify the number of cases of hyperthyroidism that followed the performance of contrast radiography in elderly patients at a geriatric hospital in a non-iodine-deficient area and to determine the clinical course of the condition.

PATIENTS AND METHODS

All patients over a 20-month period with biochemical hyperthyroidism (plasma free thyroxine level greater than 25.0 pmol/L and thyroid-stimulating hormone level less than 0.10 IU/L) were identified. Clinical features of hyperthyroidism and exposure to nonionic contrast media radiographs within the previous 12 months were sought. Follow-up extended from 6 to 22 months.

RESULTS

A total of 28 patients with hyperthyroidism (aged 70 to 96 years) were identified. Seven patients (25%) had documented biochemical development of hyperthyroidism (five) or subsequent hyperthyroidism (two) 3 to 8 weeks after nonionic contrast media radiography. The four patients who underwent scanning had a multinodular thyroid, and thyroid antibodies were not detected in five of five patients. Although the condition appeared self-limited and six of six patients were euthyroid after 18 months, the condition was not benign; progress and recovery were adversely affected by hyperthyroidism. Four patients had a good response to treatment with an antithyroid drug (carbimazole).

CONCLUSION

Iodine-induced thyrotoxicosis following contrast radiography was found in 7 of 28 cases of hyperthyroidism seen at a geriatric hospital. Although the condition appears ultimately self-limited, pharmacologic control of severe clinical features may be required. The frequency of this condition in a non-iodine-deficient area appears related to the more common occurrence of autonomous thyroid nodules in the elderly. Because performance of contrast radiography is more common in this age group, the recognition and treatment of iodine-induced thyrotoxicosis are of increasing clinical importance.

"When it rains it pours": endemic goiter, iodized salt, and David Murray Cowie, MD

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The aetiology and pathogenesis of hyperthyroidism

Studies of thyroid stimulating activity of serum from thyrotoxic patients has revealed an abnormal prolonged response in the mouse present in 40-60% of patients depending on the criteria used. This agent designated long acting thyroid stimulator (LATS) is a 7S globulin. Transplacental passage of LATS accounts for neonatal thyrotoxicosis—a self-limited disease. LATS is also more readily detected in patients with large goitre, exophthalmos, pretibial myxoedema and recurrence following therapy. Thyroid ablation is usually followed by a fall in the level of LATS. A fall may also be produced by steroid therapy or immunosuppressive agents. LATS probably arises from lymphoid tissue which accounts for the non-suppressibility of the hypersecreting thyroid. Its discovery provides strong evidence that hyperthyroidism is often, though not always, a disorder of immunological tolerance.