Differences between subjects with sufficient and deficient urinary iodine in an area of iodine sufficiency

Background: Iran has long been recognized as a country of iodine sufficiency; however, recent studies show that the proportion of subjects with insufficient urinary iodine is gradually increasing in Tehran capital city. Aim: The aim of this study was to evaluate differences between individuals with sufficient and deficient urinary iodine in Tehran. Material and methods: In this cross-sectional study, 639 Tehranian adult subjects, aged ≥19 yr (242 males, 397 females), were enroled through randomized cluster sampling. A 24-h urine sample was collected for measurement of urinary iodine, sodium and creatinine concentrations using the digestion method, flame photometry and autoanalizer assay, respectively. Salt intake was estimated and iodine content of household salt was measured by titration. Results: Medians (interquartile range) of 24-h urinary iodine concentrations in subjects with sufficient and deficient urinary iodine were 163.0 (126.0–235.0) and 44.0 (26.0–67.0) µg/l, p<0.001, respectively. Salt with iodine content of >20 parts per million was consumed by 77.4 and 38.3% of subjects with sufficient and deficient urinary iodine, respectively (p<0.001). Median daily salt intake in subjects with sufficient urinary iodine was significantly higher than in those with deficient urinary iodine (8.1 vs 7.3 g, p<0.001). No significant differences in the mentioned variables were observed between males and females. Fifty and 30% of subjects with insufficient and sufficient urinary iodine had <7 yr education, respectively (p<0.001). Conclusions: Iodine content of salt, the amount of salt intake and education levels differ greatly between subjects with sufficient and deficient urinary iodine in Tehran.