Iron Supplements Can Interact with Thyroid Meds

Many daily multivitamins and pre-natal vitamins contain iron and calcium. But did you know that these common minerals can interfere with your thyroid meds if taken at the same time?

Why do doctors recommend taking thyroid medication, usually at the same time every morning, away from food and other medication/supplements?  There are two reasons: (1) because thyroid medication is trying to replace a hormone that our body naturally produces, it makes sense to take it at the same time everyday to keep levels steady; (2) because thyroid hormone is one of those medications that have a lot of interactions with other supplements, other medications and even food.

Here are a few common supplements to avoid taking with your thyroid meds:

• Calcium supplements-several studies have shown that calcium supplements (in the studies they used calcium carbonate, citrate and acetate) lowers the absorption of levothyroxine or T4 (e.g. Synthroid). This is because calcium binds to T4.  In fact, taking T4 with calcium can lower the former’s absorption by at least 20%.  Not only that, TSH values of people who took T4 with calcium actually went up (meaning, their hypothyroidism was less controlled) from 2.7 vs 1.7 when they did not take T4 with calcium.

• Iron supplements–the binding of iron with thyroid medication seems pretty significant. In one study, when patients did not take iron with T4, their TSH was well controlled at 1.6. However, when they took ferrous sulfate (a common form of iron supplement), their TSH skyrocketed to 5.4 on average, one patient’s TSH went even as high as 29.  These are significant because a TSH above 4.5 is already considered abnormally high (for most labs). Like calcium, the mechanism is that thyroid hormone binds to iron.

Note, the take-home message is not to discontinue these supplements if there is a good reason to take them. For example, iron supplements may be important for persons with anemia and calcium supplements may be helpful for persons who are at risk for osteoporosis. Rather, the take home message is to take these supplements away from your thyroid medication.