Underactive thyroid (hypothyroidism) is a condition in which your thyroid gland doesn't make enough thyroid-stimulating hormone. Standard treatment for an underactive thyroid is daily use of the synthetic thyroid hormone levothyroxine (Levothroid, Synthroid). No research suggests that people with an underactive thyroid should avoid soy. But it's possible that eating large amounts of soy may reduce the body’s ability to absorb levothyroxine.
Other foods and drugs that may decrease absorption of this hormone include:
- A high-fiber diet
- Iron supplements (ferrous sulfate)
- Cholestyramine (Questran)
- Aluminum hydroxide, found in some antacids
- Sodium polystyrene sulfonate (Kayexelate)
- Sucralfate
With reduced absorption, signs and symptoms of an underactive thyroid may persist despite higher doses of levothyroxine. Blood tests can detect if this is occurring. If you take thyroid-stimulating hormone, tell your doctor if you take any medications or dietary or herbal supplements.
