OBJECTIVE: The pattern of thyroid dysfunction seems to depend on the iodine status of the population. Prevalence of thyroid dysfunction could be a parameter to consider when evaluating iodine deficiency disorders in a population. DESIGN: Comparative cross-sectional investigation in two regions in Denmark with marginally different iodine excretion. METHODS: A random selection of 4649 participants from the Civil Registration System in Denmark in age groups between 18 and 65 years were examined. Thyroid dysfunction was evaluated from blood samples and questionnaires, and compared with results from ultrasonography. RESULTS: Median iodine excretion was 53 microg/l in Aalborg and 68 microg/l in Copenhagen. Previously diagnosed thyroid dysfunction was found with the same prevalence in the regions. Serum TSH was lower in Aalborg than in Copenhagen (P=0. 003) and declined with age in Aalborg, but not in Copenhagen. Not previously diagnosed hyperthyroidism was found with the same overall prevalence in the regions, but in age >40 years hyperthyroidism was more prevalent in Aalborg (1.3 vs 0.5%, P=0.017). Not previously diagnosed hypothyroidism was found more frequently in Aalborg (0.6 vs 0.2%, P=0.03). Hyperthyroidism was more often associated with macronodular thyroid structure at ultrasound in Aalborg and hypothyroidism was more often associated with patchy thyroid structure in Copenhagen. CONCLUSIONS: Significant differences in thyroid dysfunction were found between the regions with a minor difference in iodine excretion. The findings are in agreement with a higher prevalence of thyroid autonomy among the elderly in the most iodine-deficient region.
Thyroid disorders are common with occurrence primarily determined by the availability of dietary iodine. Iodine fortification programmes are internationally recommended to ensure sufficient iodine intake in populations. An understanding of the role of thyroid hormone levels within the normal range, set points and etiological factors related to thyroid disease development is important for optimal prevention and treatment. Limited data, however, exist regarding the impact of iodine fortification on thyroid function development. Additionally, the relation between body weight and thyrotropin (TSH) within the normal range and the role of female reproductive factors in the etiology of thyroid autoimmunity is debated.
The aim of this PhD project was to analyse the effect of a nationwide iodine fortification programme on individual development in thyroid function and to identify concurrent determinants for the possible changes. Furthermore, we aimed to investigate the association between weight and serum TSH change as well as the association between female reproductive factors and change in TSH and thyroid peroxidase antibody (TPO-Ab) status.
A longitudinal population-based study of the DanThyr C1 cohort examined before (1997-1998) and after (2008-2010) the introduction of mandatory iodine fortification of salt on July 1 2000. A total of 2,465 individuals participated in the follow-up examination. The main outcome measure was change in serum TSH. Change in TPO-Ab status was additionally used in Paper III.
Urinary iodine excretion levels increased significantly during follow-up. Serum TSH also increased significantly, most pronounced in the region with the highest iodine intake, whereas the increase was not significant in the low-iodine-intake region. The presence of TPO-Ab at baseline and absence of goitre and multiple nodules were identified as determinants of TSH increase. Moreover, a low-normal TSH at baseline was a determinant of future decreased serum TSH, while likewise a high-normal baseline TSH values determined a TSH above normal reference range at follow-up. A positive association between 11-year serum TSH change and weight change was found, but without baseline body mass index being a determinant of future weight change and without baseline TSH being a determinant of future weight change. An inverse association between the time on HRT treatment and the risk of increased TPO-Ab status during follow-up was found, but the association was not significant when applying the Bonferroni adjusted significance level and not associated with TSH change. Parity, OCP use, abortions, age at menarche and menopausal status were associated neither with TSH change nor with increased TPO-Ab status during follow-up.
TSH increased significantly, and the difference be-tween regions with different iodine intakes could indicate that iodine, at least partly, explains the TSH increase. The identified determinants of TSH change may indicate that susceptible individuals were subject to well-known adverse effects of iodine fortification. The predictive value of TSH on future TSH levels suggests a gradual development of thyroid disease. Whether body weight and TSH are causally connected remains to be proven. These results are an important contribution to the discussion of the role of thyroid hormones level within the normal range, set points and the association with body weight. A minor role, if any, is suggested for the studied female reproductive factors in development of thyroid autoimmunity. The longitudinal study neither solves the problem of causality nor is of the optimal design to measure the impact of iodization of salt, but can be informative in the study of determinants.
Studies on the immediate and long-term effects of radiation on the B-system immunity of children who were affected by radiation after the Chernobyl disaster (from 1986-1992) are summarized in this paper. Complete clinical and immunological examination of more than 6000 children have been carried out. The dynamics of the immune system, with ongoing reactions of cell proliferation and differentiation, gene amplification, transcription, translation, biosynthesis and switching production of isotypes and subclasses of immunoglobulins, as well as specific and nonspecific (natural) antibodies, make it highly susceptible to the action of radiation in addition to other ecological factors. B-system of immunity (B-cel level, concentration of immunoglobulins-M, G, A, E; subclasses of IgG (IgG1-IgG4) in the serum and saliva, and the level of nonspecific heterophilic autoantibodies (RF, antithyroglobulin) were investigated in children of differing ages and sex living in the territories of the Republic of Belarus contaminated with radionuclides. Research showed decreased levels of B-cell and IgM and IgG isotopes 40-50 days after the disaster and increased levels of IgA immunoglobulins at that time. Long-term effects of low doses of radiation showed increased concentrations of IgM and IgG, correlating changes in the B-system of immunity with the level of 137Cs contamination in the territory of residence and also with the amount of 137Cs found in the children.
Endemic goitre of moderate severity was mainly found in the east of Finland in the 1930's. Studies in the 1950's showed an average daily iodine intake of 65-70 micrograms in the west and 50-65 micrograms in the east of the country. The use of iodized salt was introduced in the late 1940's but added only 15 micrograms of iodine to the daily intake. In the late 1950's iodine prophylaxis was intensified and the use of salt containing 25 mg KI/kg was recommended. In 1978 about 95% of all household salt used in the Savonlinna area was iodized. This region in the east of Finland has been used as an area of surveillance and studies have been carried out there in 1959, 1969 and 1979. During this period the thyroidal uptake decreased from 67 to 23% in non-goitrous subjects and from 62 to 28% in goitre patients the difference between the two last figures being statistically significant. The goitre patients also had significantly higher serum thyroxine and triiodothyronine levels. During the same period the urinary excretion of stable 127I increased from 45 micrograms to about 250 micrograms a day. Concomitantly the goitre prevalence among school children has decreased. Having been in the early 1950's in most parts 15-30% it is generally now 1-4%. It seems that the iodine intake is now adequate and that the endemia is gradually subsiding.
To study hyperthyroidism in long-term iodine sufficiency (IS), as iodine supply affects its occurrence.
Prospective descriptive study.
In 2003-2005, all referred cases of subclinical (SH) and overt hyperthyroidism (OH) were registered at diagnosis from a population (n = 631 239) in Gothenburg, Sweden.
Information on age, gender, smoking, thyroid associated ophthalmopathy (TAO), thyroid hormones and TSH receptor antibodies (TRab) was collected. Incidences were calculated. SH and OH cases with Graves' disease (GD), toxic multinodular goiter (TMNG) and solitary toxic adenoma (STA) were compared. In GD, TRab+ and TRab- cases and patients with (TAO+) and without TAO (TAO-) were compared.
The total incidence (n/100 000/year) of hyperthyroidism was 27·6; OH 23·8; SH 3·8; GD 21·4; TMNG 4·3; and STA 1·8. SH was more common among TMNG (40·2%) and STA (45·7%) than in GD (5·9%). SH-GD patients were older, more often smokers and had lower TRab levels than OH-GD patients. FreeT4 and T3 levels in GD were higher than in TMNG and STA. FreeT4, T3 and TRab decreased with age in patients with GD, P
Dietary iodine is important to human health, and both low and high iodine intake levels increase the risk of disease. Seaweed is rich in iodine and it is a common component in both Asian and in Arctic cuisines. While the intake and impact are known for Asian people, data are lacking for Arctic people. We aimed to (1) measure iodine content of dietary seaweeds in Greenland, (2) estimate iodine absorption, and (3) assess the impact on iodine intake in Arctic people. A hunter in East Greenland donated household seaweed for (1) measurement of iodine content and (2) ingestion of 45?g by each of eight individuals with subsequent urine collections. (3) In Ammassalik, 96% of 50-69-year-old Inuit reported on the frequency of intake of seaweed and provided a spot urine sample for iodine measurement. Seaweed species provided were Chondrus crispus and Ascophyllum nodosum. (1) The iodine content was 47 and 102?mg/g, respectively. (2) An estimated 1.1 and 1.9?mg of the ingested 2.1 and 4.6 of iodine in seaweed were excreted in the urine within 2 days. (3) More than two in three Inuit reported some dietary use, and 41% (109 of 268) reported a weekly intake of dietary seaweed, which was associated with iodine excretion. In conclusion, the iodine content of edible seaweeds in the Arctic is very high and bioavailable. Dietary intake contributed to the recommended iodine intake level, but marked variation in iodine excretion calls for evaluation of the impact on thyroid function.
Department of Nutrition, Institute of Basic Medical Sciences, University of Oslo, P.O. Box 1046 Blindern, 0317 Oslo, Norway; Department of Nutrition and Public Health, Faculty of Health and Sport Sciences, University of Agder, 4630 Kristiansand, Norway. Electronic address: firstname.lastname@example.org.
Iodine is crucial for normal growth and neurodevelopment. Before 1950, goitre caused by iodine deficiency was widespread in Norway, but decreased significantly after mandatory fortification of animal fodder. Recent dietary changes in milk consumption and fish intake may again have increased the risk of inadequate intakes in some population groups in Norway. The situation for children and adolescents is unclear, and data from nationally representative studies are highly needed. We aimed to describe the iodine intake in Norwegian children and adolescents and estimate the proportion of individuals with an increased risk of suboptimal, adequate and excessive usual iodine intake. In addition, we aimed to investigate whether individuals' characteristics were associated with iodine intake, and to identify the major iodine contributing foods in the diet of this population.
Data from 1722 individuals (4-, 9- and 13-year-olds) from a national dietary survey in Norway from 2015-2016 was used. Both descriptive and inferential statistics were conducted. Usual iodine intakes were estimated, stratified by age group and sex and compared to dietary reference intake cut-offs. Linear regression models were used to assess the association between iodine intake and participants' characteristics. The contribution of iodine from different foods was described for all and across different participant groups.
We estimated that the proportion of participants with an increased risk of a suboptimal usual intake of iodine varied from 3-36%. A significant increased risk was observed for older children and girls compared to younger children and boys. Excessive usual intakes were not observed in any age group. Iodine intake was associated with sex, maternal educational level and area of residence. A lower intake was observed for girls and those with a mother with a low educational level. Moreover, those living in the western part and Mid-Norway had statistically significantly higher intakes compared to those living in the capital city and surroundings. Milk, milk products, cheese, fish and shellfish were the main contributors to iodine intake. Supplements contributed with very little of the total iodine intake.
We have shown that the estimated risk of suboptimal usual iodine intakes among children and adolescents in Norway varies according to age, sex, maternal educational level and area of residence. Those with a limited intake of the main dietary contributors to iodine intake may be at risk, and adolescent girls seem to be especially vulnerable.