Iodine intakes of 100–300 μg/d do not modify thyroid function and have modest anti-inflammatory effects

Abstract

Little information is available as to whether doses of iodide similar to those recommended in clinical practice for the prevention of iodine deficiency in pregnant women affect thyroid function. The aim of the present study was to analyse whether doses of iodide can affect thyroid function in adults, and evaluate its effect on plasma markers of oxidative stress, inflammation and acute-phase proteins. A total of thirty healthy volunteers (ten men and twenty women) with normal thyroid function were randomly assigned to three groups (n 10). Each group received a daily dose of 100, 200 or 300 mg of iodide in the form of KI for 6 months. Free tetraiodothyronine (FT4) levels at day 60 of the study were higher in the groups treated with 200 and 300 mg (P¼0·01), and correlated with the increase in urinary iodine (r 0·50, P¼0·007). This correlation lost its significance after adjustment for the baseline FT4. The baseline urinary iodine and FT4 correlated positively with the baseline glutathione peroxidase. On day 60, urinary iodine correlated with C-reactive protein (r 0·461, P¼ 0·018), and free triiodothyronine correlated with IL-6 (r 20·429, P¼0·025). On day 60, the changes produced in urinary iodine correlated significantly with the changes produced in a1-antitrypsin (r 0·475, P¼ 0·014) and ceruloplasmin (r 0·599, P¼ 0·001). The changes in thyroid-stimulating hormone correlated significantly with the changes in a1-antitrypsin (r 20·521, P¼0·005) and ceruloplasmin (r 20·459, P¼ 0·016). In conclusion, the administration of an iodide supplement between 100 and 300 mg/d did not modify thyroid function in a population with adequate iodine intake. The results also showed a slight anti-inflammatory and antioxidative action of iodide.

Does Dietary Iodine Regulate Oxidative Stress and Adiponectin Levels in Human Breast Milk?

“…The breast concentrates iodine in higher levels than serum and this could have different effects; the in vitro inhibition of adiponectin expression by iodide is observed with doses similar to breast milk iodine levels, but not with iodide doses similar to serum levels. On the other hand, low iodine doses can have a slight and chronic antioxidant effect, as we have demonstrated in a previous study (4). However, the relation between iodine and adipokines is not well known.…”

“…No significant correlations were found between the baseline serum adiponectin and urinary iodine concentrations, either in the casual (r = -0.095, Neither were significant correlations found after adjusting for glucose levels (r = -0.065, p = 0.750 and r = -0.064, p = 0.589, respectively). After 2 months of treatment, the urinary iodine concentration increased significantly in the casual samples (4) and in the 24-h urinary samples (100 group: 191.6 -90.3 vs. 223.3 -91.7 lg/day, p = 0.063; 200 group: 140.3 -74.6 vs. 230.4 -130.9 lg/day, p = 0.032, and 300 group: 200.6 -56.4 vs. 377.0 -179.4 lg/day, p = 0.011). Serum adiponectin did not change significantly in the three groups, either separately or in all the subjects together (data not shown).…”

“…Iodide was found to effectively scavenge reactive oxygen species (ROS) in human blood cells, decreasing damage by free oxygen radicals. In addition, iodide intake also seems to be related to the activity of the enzymes glutathione peroxidase (GSH-Px), superoxide dismutase (SOD), and catalase (3,4). However, little information is available about the relation between the iodine status of lactating mothers and the antioxidant capacity of human breast milk.…”

“…The second study was carried out in thirty healthy volunteers, with a normal thyroid function, supplemented with a daily dose of 100, 200, or 300 lg KI for 2 months, doses similar to those usually recommended in clinical practice for the prevention of iodine deficiency in pregnant women (4). In these subjects, the mean baseline serum adiponectin concentration was 10.7 -4.1 ng/ml, and the mean baseline urinary iodine concentration was 173.8 -73.8 lg/L in the casual samples and 180.1 -76.8 lg/day in the 24-h urinary samples, with no significant differences between the three groups of subjects (100, 200, and 300 groups).…”

“…The iodine concentration in urine and human milk samples was measured by the modified Benotti and Benotti technique (4,8). The intra-and interassay coefficients of variation of the urinary iodine assay were 2.01% and 4.53%, respectively.…”