I With a decrease in the addition of salt to food, iodine deficiency diseases are re-emerging globally. Public Health officials are considering the addition of iodine salts to processed foods to redress this situation. However, iodate is a powerful oxidising agent and iodide, a powerful reducing agent. Their use in foods may result in redox reactions which in turn may influence food characteristics, shelf life and stability. Very little research has been conducted with respect to the reactions of iodine and its salts in food matrices. Thus, the impact of fortifying processed foods with iodine salts is unclear. An increased incidence of overt hypothyroidism after iodine fortification of salt in Denmark: A prospective population studyInge Bülow Pedersen*,Department of Endocrinology and Medicine, Aalborg Hospital, Aarhus University Hospital; Endocrine Unit, Medical Clinic I, Bispebjerg Hospital; Research Centre for Prevention and Health, Glostrup University Hospital; The National Heart Foundation, Copenhagen; Department of Nutrition, National Food Institute
Iodine fortification (IF) of salt was introduced in Denmark in 1998. Little is known about the effect of a minor increase in iodine intake on the incidence of hypothyroidism. We prospectively identified all new cases of hypothyroidism in two areas of Denmark prior to and 7 years after Iodine had been introduced. Results: The overall incidence rate of hypothyroidism increased during the study period (baseline: 38.3/100,000/year; voluntary IF: 43.7 (vs. baseline: ns); early mandatory IF: 48.7 (vs. baseline: rate ratio (RR) (95% confidence interval (CI)):1.27 (1.10-1.47)); late mandatory IF: 47.2 (vs. baseline: RR (CI): 1.23 (1.07-1.42)). There was a geographic difference ashypothyroidism increased only in the area with previous moderate ID (Aalborg, late mandatory IF vs. baseline: 40.3/29.7, RR (CI):1.35 (1.11-1.66); Copenhagen: 56.7/51.6, RR (CI): 1.10 (0.90-1.34)). The increase occurred in young and middle aged adults. Conclusion: Even a cautious iodization of salt was accompanied by a moderate increase in the incidence rate of overt hypothyroidism. This occurred primarily in young and middle aged subjects with previousmoderate ID.
The Danish investigation on iodine intake and thyroid disease, DanThyr: status and perspectivesDepartment of Endocrinology and Medicine, Aalborg Hospital, DK-9000 Aalborg, Denmark, 1 Danish Institute for Food and Veterinary Research, Copenhagen, Denmark, 2 Research Centre for Disease Prevention and Health, Glostrup Hospital, Copenhagen, Denmark, 3 Medical Clinic I, Bispebjerg Hospital, Copenhagen, Denmark and 4 The National Heart Foundation, Copenhagen, Denmark
Objective: Denmark was an area of iodine deficiency, and mandatory iodine fortification of table salt and salt in bread (13 p.p.m. iodine) was initiated in 2000/2001. The Danish investigation on iodine intake and thyroid disease (DanThyr) is the monitoring of the iodine fortification program. Results: The study showed profound effects of even small differences in iodine intake level on the prevalence of goiter, nodules,and thyroid dysfunction. Mild and moderate iodine deficiency was associated with a decrease in serum TSH with age. Other environmental factors were also important for goiter development (increase in risk, smoking and pregnancy; decrease in risk, oral contraception and alcohol consumption), and the individual risk depended on the genetic background. Environmental factors had only a minor influence on the prevalence of thyroid autoantibodies in the population. There were more cases of overt hypothyroidism in mild than in moderate iodine deficiency caused by a 53% higher incidence of spontaneous (presumably autoimmune) hypothyroidism. On the other hand, there were 49% more cases of overt hyperthyroidism in the area with moderate iodine deficiency. The cautious iodinefortification program, aiming at an average increase in iodine intake of 50 µg/day has been associated with a 50% increase in incidence of hyperthyroidism in the area with the most severe iodine deficiency. The incidence is expected to decrease in the future, but there may be more cases of Graves’ hyperthyroidism in young people. Conclusion: A number of environmental factors influence the epidemiology of thyroid disorders, and even relatively smallabnormalities and differences in the level of iodine intake of a population have profound effects on the occurrence of thyroidabnormalities. Monitoring and adjustment of iodine intake in the population is an important part of preventive medicine.
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