The incidence of
thyrotoxicosis in northern Tasmania rose significantly in 1964, two years before an epidemic of
iodine-induced
thyrotoxicosis was precipitated by the addition of
iodate to bread to prevent goitre. Each time older patients accounted for most of the increase. The 1964 increase was probably
iodine-induced as the use of iodophor
disinfectants on dairy farms, which causes
iodine residues in milk, began in 1963 and a fall in the prevalence of goitre in young children suggested an increase in dietary
iodine at about that time. A further small increase in
thyrotoxicosis in 1971 may also have been
iodine-induced as it followed an extension of the use of
iodophors. Dietary
iodine is rising substantially in many places because of high
iodine levels in milk and the use of
iodine compounds in automated bread making, and this may be causing unsuspected
iodine-induced
thyrotoxicosis. Dietary
iodine should be monitored regularly and clinicans alerted to any rise. Contamination of common foods with
iodine should be more strictly controlled.