Endemic goitre in Finland and changes during 30 years of iodine prophylaxis

Endemic goitre of moderate severity was mainly found in the East of Finland still in the 1950s but the whole country was moderately iodine deficient. The daily iodine intake determined both from food consumption and from the urinary excretion in population samples was 50-70 micrograms being lower in the East. The main iodine sources were milk products, about 50% of the daily intake being derived from these. Iodized salt was available but its use was very low and the iodine content insufficient so that only about 20% came from this source. In the late 1950s iodine prophylaxis was activated and since then only salt containing 25 mg KI/kg has been imported. However, during the last decades the consumption of salt has declined from 7-8 g to less than 4 g per day. Today the iodine intake in Finland is about 300 micrograms per day, the highest in Europe. The main sources are milk products and eggs which provide about 2/3 of the daily iodine intake due to an active iodine prophylaxis of house animals and only 20% comes from iodized salt. The origin of endemic goitre in Finland has obviously been multifactorial autoimmunity, natural goitrogens and possibly genetic factors being superimposed upon the basic iodine deficiency. The iodine supply is now adequate and there is no more goitre in neonates and no endemic goitre in school children in whom the prevalence is usually below 1%. Concomitantly, the nosology of hyperthyroidism has changed. Whereas more than 80% of hyperthyroid patients in the 1950s had nodular goitre the main type of hyperthyroidism today is Graves' disease proper with a small or normal-sized thyroid gland without nodules obviously due to disappearance of the endemic nodular goitre.