Radioiodine kinetics and thyroid function following the universal salt iodization policy

Background Universal salt iodization was introduced in Delhi in 1989. The p resent study quantifies the change in iodine kinetics as a result of this. The previous values were reported 10-30 years earlier, when Delhi was iodin e deficient. Methods. Thirty subjects (18 men and 12 women, 17-48 years of age) who were residents of Delhi and had no thyroid disorder, were recruited From our ou tpatient clinic in 1999. The 24-hour urinary excretion of iodine and the io dine content of salt consumed at home by these subjects were estimated. Kin etic studies of iodine using radiotracer I-131 were done to determine thyro id iodine clearance, renal iodine clearance, percentage uptake and absolute iodine uptake by the thyroid gland, and plasma inorganic iodine. Results, The median 24-hour urinary iodine excretion was 341.3 Gig. The mea n (SD) thyroid uptake of radioactive iodine was 4.9 (2.3)% at 2 hours and 1 9.1 (8.0)% at 24 hours. The median calculated plasma inorganic iodine was 1 .36 mug/dl, absolute iodine intake 6.5 mug/hour and thyroid iodine clearanc e was 4.8 ml/minute (geometric means 1.68 mug/dl, 8.5 mug/hour and 8.1 ml/m inute, respectively). The serum thyroid hormones and thyroid stimulating ho rmone were within normal limits. Conclusion. Compared to the values reported 10-30 years ago when the popula tion was iodine deficient, the present urinary iodine excretion, plasma ino rganic iodine and absolute iodine intake have increased, while the percenta ge thyroid uptake of iodine ingested and thyroid clearance have decreased. The lack of change in the serum thyroid hormone levels after 10 years of un iversal salt iodization indicates that iodine consumption has had no advers e effect on thyroid function in these normal individuals. These changes are consistent with the increase in iodine consumption, Since the iodine inges tion in a community may change with time, assessment of iodine kinetics sho uld be done periodically in different regions of the country.