TABLE 11.
Goitrogens and micronutrient deficiencies that affect iodine metabolism and thyroid function1
| Mechanism | |
| Cassava, lima beans, linseed, sorghum, sweet potato | Contain cyanogenic glucosides that are metabolized to thiocyanates and act by competing with iodine for uptake by thyroid gland |
| Cruciferous vegetables: cabbage, kale, cauliflower, broccoli, turnips, rapeseed | Contain glucosinolates; these metabolites act by competing with iodine for thyroidal uptake (36) |
| Soy, millet | Flavonoids impair thyroid peroxidase activity |
| Industrial pollutants (that enter food and water) | |
| Perchlorate, nitrate | Competitive inhibitors of the sodium/iodide symporter; they act by decreasing transportation of iodine to the thyroid |
| Others (e.g., disulfides from coal processes) | Reduce thyroidal iodine uptake |
| Smoking | One of the important goitrogens; during breastfeeding, smoking is known to be linked to reduced iodine content in the breast milk; the mechanism behind this is that in smoking women, the higher serum concentrations of thiocyanate compete with iodine for active transport into the secretory epithelium of the lactating breast (35) |
| Nutrients | |
| Selenium deficiency | Accumulated peroxides due to selenium deficiency may damage the thyroid, and deiodinase deficiency may impair the synthesis of thyroid hormone |
| Iron deficiency | The activity of heme-dependent TPO is reduced and the efficacy of iodine prophylaxis may be compromised |
| Vitamin A deficiency | Due to the deficiency there is a decrease in vitamin A–mediated suppression of the pituitary TSHβ gene and an associated increase in TSH stimulation and goiter |
1
TPO, thyroperoxidase; TSH, thyroid-stimulating hormone.