Effects of administration of iron, iodine and simultaneous iron-plus-iodine on the thyroid hormone profile in iron-deficient adolescent Iranian girls.

Objective: To investigate whether iron supplementation can improve thyroid hormone function in iron-deficient adolescent girls.

Design: A double-blind randomized intervention study.

Setting: The study was performed from 2002 through 2003 in the Islamic Republic of Iran.

Subjects: 103 iron-deficient non-anaemic girls who fulfilled all inclusion criteria were included, and 94 subjects successfully completed the study.

Interventions: Patients were randomly assigned to one of four groups and treated with a single oral dose of 190 mg iodine plus 300 mg ferrous sulphate 5 times/week (n=24), 300 mg ferrous sulphate 5 times/week (n=23), a single oral dose of 190 mg iodine (n=25), or a placebo (n=22) for 12 weeks.

Results: All groups were comparable at baseline. After the intervention, there was a significant increase in ferritin and transferrin saturation in the iron+iodine group (17.6 vs 8.7 microg/dl, and 18.8 vs 7.2%, respectively, P<0.001 for both) and in the iron group (P<0.001 for both). Urinary iodine doubled in the iron+iodine group and in the iodine group (P<0.001 for both). Thyroid indices tT4, tT3 and T3RU increased and reverse RT3 decreased in the iron+iodine group (10 vs 8.9 microg/dl, P< 0.001; 143 vs 138 microg/dl, P<0.05; 32.3 vs 28.4%, P<0.001 and 24.8 vs 44.2 ng/dl, P<0.001, respectively) and in the iron group. These two groups did not differ for any of the four indices, but both differed significantly from the iodine and placebo groups.

Conclusions: Our results indicate that improvement of iron status was accompanied by an improvement in some indices of thyroid hormones.

Sponsorship: This study was supported by the Dean of Research Affairs of the Tehran University of Medical Sciences.