Effect of lifelong iodine supplementation on thyroid 131-I uptake: a decrease in uptake in euthyroid but not hyperthyroid individuals compared to observations 50 years ago.
BACKGROUND
In Sweden, iodine has been added to table salt (10 mg/kg) since 1936; this amount was increased in 1966 to 50 mg/kg.


OBJECTIVE
To investigate a euthyroid Swedish population (n = 44, 60-65 years) with its entire lifespan with iodine supplementation as for 24-h 131-I uptake (24 h IU) and thyroid nodularity (thyroid scintigraphy). To compare the euthyroid 24 h IU with uptake of thyrotoxic individuals, and with observations from 1955.


METHODS
The 24 h IU was used in euthyroid individuals after oral administration of 0.1 MBq/2.7 microCi radioiodine and imaging of the thyroid gland was carried out using 99mTc-pertechnetate.


RESULTS
In 1999-2000, the mean 24 h IU in the euthyroid individuals was 21% (range 11-33%) and the normal (central 95%) reference interval was 14-30%. Scintigraphy suggested multinodular goitre in three euthyroid individuals. In Graves' patients (n = 53, 50-65 years), the mean 24 h IU was 61% (range 29-89%). In 1955, the 24 h IU in euthyroid individuals was higher (38%, range 10-70%), while hyperthyroid patients had uptake values similar to those recorded in the present investigation (mean 62%, range 40-90%).


CONCLUSIONS
The population sample studied had to be small for ethical reasons. We conclude that the reference interval for 24 h IU is 14-30% in this population that had spent its entire lifespan with iodine supplementation. This is lower than that recorded in a Swedish euthyroid population half a century ago having had low-grade table-salt iodine supplementation for 20 years. Values for hyperthyroid patients, however, do not appear to have been affected likewise.
Milakovic
M
M
Mölnlycke Primary Health Care and Research Centre, Department of Primary Health Care, Sahlgrenska Academy at Göteborg University, Sweden.
Berg
G
G
Eggertsen
R
R
Nyström
E
E
D000368:Aged; D005260:Female; D006801:Humans; D006980:Hyperthyroidism / Q000000981:diagnostic imaging / Q000378:metabolism*; D007037:Hypothyroidism / Q000000981:diagnostic imaging / Q000378:metabolism*; D007455:Iodine / Q000008:administration & dosage* / Q000627:therapeutic use; D007457:Iodine Radioisotopes / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D011877:Radionuclide Imaging / Q000379:methods; D017673:Sodium Chloride, Dietary / Q000008:administration & dosage* / Q000627:therapeutic use; D013548:Sweden; D013961:Thyroid Gland / Q000000981:diagnostic imaging* / Q000378:metabolism*; D013997:Time Factors
D007457:Iodine Radioisotopes; D017673:Sodium Chloride, Dietary; C034024:iodized salt; D007455:Iodine