N. Knudsen

Environmental Iodine Intake Affects the Type of Nonmalignant Thyroid Disease

The relationship between the iodine intake level of a population and the occurrence of thyroid diseases is U-shaped with an increase in risk from both low and high iodine intakes. Developmental brain disorders and endemic goiter caused by severe iodine deficiency may seriously deteriorate overall health status and economic performance of a population. Severe iodine deficiency with a median 24-hour urinary iodine excretion of the population below 25 microg needs immediate attention and correction. Less severe iodine deficiency with median urinary iodine excretion below 120 microg per 24 hours is associated with multinodular autonomous growth and function of the thyroid gland leading to goiter and hyperthyroidism in middle aged and elderly subjects. The lower the iodine intake, the earlier and more prominent are the abnormalities. At the other end of the spectrum, severely excessive iodine intake starting at median urinary iodine excretion levels around 800 microg per 24 hours is associated with a higher prevalence of thyroid hypofunction and goiter in children. A number of studies indicate that moderate and mild iodine excess (median urinary iodine >220 microg per 24 hours) are associated with a more frequent occurrence of hypothyroidism, especially in elderly subjects. The exact mechanism leading to this has not been clarified, and more studies are needed to define the limits of excessive iodine intake precisely. Due to the frequent occurrence of thyroid disorders, proper monitoring and control of the population iodine intake level is a cost-effective alternative to diagnosing, therapy and control of the many individual cases of thyroid diseases that might have been prevented.

Goitre prevalence and thyroid abnormalities at ultrasonography : a comparative epidemiological study in two regions with slightly different iodine status

The association between severe iodine deficiency and endemic goitre is well established, but little information is available on the relation between milder degrees of iodine deficiency and goitre prevalence.

Dietary iodine intake and urinary iodine excretion in a Danish population: effect of geography, supplements and food choice

I deficiency diseases remain a health problem even in some developed countries. Therefore, measurement of I intake and knowledge about food choice related to I intake is important. We examined I intake in 4649 randomly selected participants from two cities in Denmark (Copenhagen and Aalborg) with an expected difference in I intake. I intake was assessed both by a food frequency questionnaire and by measuring I in casual urine samples. I excretion was expressed as a concentration and as estimated 24-h l excretion. Further, subgroups with low I intake were recognized. I intake was lower in Aalborg than in Copenhagen for all expressions, and lower than recommended in both cities if I intake from supplements was not included. Milk was the most important I source, accounting for about 44% of the I intake, and milk (P<0.001) and fish (P=0.009) intake was related to I excretion in a multiple linear regression model. Thus, risk groups for low I intake were individuals with a low milk intake, those with a low intake of fish and milk, those not taking I supplements and those living in Aalborg where the I content in drinking water is lower. Even individuals who followed the advice regarding intake of 200-300 g fish/week and 0.5 litres milk/d had an intake below the recommended level if living in Aalborg.

Evaluation of a semi-quantitative food frequency questionnaire to estimate iodine intake

Objective: To evaluate a food frequency questionnaire (FFQ) used to assess the dietary intake of iodine.Design: The iodine intake determined by the FFQ was compared with 4-day dietary records and with iodine excretion in 24 h urine samples in a subgroup of participants in a cross-sectional study of iodine intake and thyroid diseases in Denmark. Furthermore, the intake of fish determined from the FFQ was compared with the intake of fish from a simple record kept for 3 months.Subjects: Women aged 25–30 y and 60–65 y.Results: Median iodine intake was similar when determined from the FFQ and from dietary records and the correlation between these measures was 0.52 (P<0.001). Iodine intake was higher than iodine excretion (P<0.001). The cross-check questions in the FFQ (for example the question ‘How often did you get any kind of fish?’) underestimated the intake. In contrast, the intake of a specific fish tended to be overestimated by the FFQ when compared with the 3 month record of fish intake.Conclusion: The FFQ can be used to classify subjects into low and high iodine intake groups, but the level of iodine tends to be overestimated.Sponsorship: The Danish Medical Foundation and the 1991 Pharmacy Foundation.European Journal of Clinical Nutrition (2001) 55, 287–292

Iodine intake and incidence of thyroid cancer in Denmark

Objective  Iodine intake is suspected to be a risk factor for thyroid cancer. Eastern Denmark is characterized by mild and western Denmark by moderate iodine deficiency, and this difference is associated with a 50% difference in the occurrence of goitre and thyrotoxicosis. The objective of the study was to determine whether the incidence of thyroid cancer differs between these two regions, as any difference would have important safety implications for the national iodine supplementation programme.

The U-Shaped Curve of Iodine Intake and Thyroid Disorders

The association between iodine intake level and the risk of disease is U-shaped, as both low and high iodine intakes are associated with an increase in the risk of thyroid problems. The curve is nonsymmetrical with the most serious problems associated with iodine deficiency, which should be corrected. Both low and high iodine intakes are associated with an increase in the risk of thyroid problems. The most serious problems are associated with iodine deficiency, which should be corrected. However, the iodine intake should only be brought to the level where iodine deficiency disorders are avoided. Optimally, the iodization program should be planned to keep population iodine intake within a relatively narrow range around the recommended level. To compensate for the low iodine supply that was previously highly prevalent in the world, complex mechanisms have been developed in the thyroid gland. Mechanisms are able to accumulate and utilize even very small supplies of iodine. The thyroid immediately reacts to a sudden load of iodine to avoid overproduction of thyroid hormone. As usual when complex mechanisms are involved, this leads to a risk of malfunction—and disease.