Further decrease in thyroidal uptake and disappearance of endemic goitre in children after 30 years of iodine prophylaxis in the east of Finland.

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.