Current incidence of thyrotoxicosis and past prevalence of goitre in 12 British towns.

The incidence of thyrotoxicosis was determined in a collaborative study in 12 towns in England and Wales. Cases were ascertained prospectively through biochemistry laboratories carrying out routine thyroid function tests. The annual incidence varied from 9.7 to 49.2 per 100 000. Reassay of sera at a reference laboratory showed that this variation did not result from inter-laboratory differences in the techniques for measuring thyroid function. The incidence of thyrotoxicosis was strongly correlated with the previous prevalence of endemic goitre in the towns. Current high dietary intakes of iodine--largely the result of milk contamination--may cause toxic nodular goitre in people made susceptible by a lack of iodine early in life. They may also contribute to the occurrence of Graves' disease.