Possible Interaction: Thyroxine and Iron, Dietary

“The interaction is probably caused by the binding of iron to thyroxine.”

“When iron and thyroxine were mixed together in vitro, a poorly soluble purple complex appeared that indicated the binding of iron to thyroxine.”

“Other factors reported by … could adversely affect levothyroxine absorption included use of prescription medications (20.6 %) and over-the-counter medications (34.3 %) … treat comorbid gastrointestinal (GI) conditions; use of dietary supplements (51.8 %, primarily calcium and iron ); and intake of foods/beverages high …, iodine, or soy (68.0 %).”

“Despite discontinuation of iron and statin which are known to interfere with thyroxine absorption and crushing of thyroxine tablets to enhance absorption, his TSH remained elevated.”

“Certain drugs, such as iron and calcium, reduce the gastrointestinal absorption of levothyroxine.”

“Foods containing large amounts of soybean, fiber, or iron should not be used for administering levothyroxine (Prod Info Synthroid oral tablets, 2005).”

“You should continue to monitor her TSH levels carefully and be aware that iron given during pregnancy might form an insoluble complex with thyroxine in the gestational tract.”

“Decreased bioavailability induced by simultaneous intake of other medications (eg, aluminum-containing antacids, iron , cholestyramine, sucralfate) is a well-known occurrence with levothyroxine therapy.1 Decreased absorption could similarly account for the calcium carbonate effect.”

“We conclude that hyperthyroidism induces SOD activity in liver; ferritin levels increase in hyperthyroidism, contributing to the antioxidant defense system; GSH-Px and … decreased significantly in hyperthyroidism either due to inactivation due to increased oxidative stress or to insufficient synthesis; iron supple- and GPT analysis); iron decreases … of T4.”

“ Thyroxine acted against effects of iron.”

“ Thyroxine also removed the iron influence upon copper deposition.”

“The administration of thyroxine produces a significant increase in the copper, magnesium, iron and zinc contents of liver, with a concomitant decrease of heart iron.”