Published April 18 2016
In this article I’m going to discuss some of the common nutrient and drug interactions for those people who are taking thyroid hormone medication. This information applies not only to those people who are taking synthetic thyroid hormone, but also for those taking natural thyroid hormone medication. I’m going to start off by mentioning some foods which can decrease absorption followed by individual nutrients. I’ll also list a few medications which can interact with thyroid hormone medication.
Foods Which Can Decrease Absorption. Although most people who take thyroid hormone medication are aware that they should take it on an empty stomach and then wait at least 30 minutes before eating breakfast, there are some foods which have been shown to specifically interfere with thyroid hormone medication, and thus it probably would be wise to wait a little longer before consuming these. The absorption of thyroid hormone medication can be decreased by soybean flour, cottonseed meal, walnuts and calcium fortified juices (1) . With regards to soy, a case study showed that administration of Levothyroxine with a soy protein dietary supplement resulted in decreased absorption of the medication (2) . Drinking grapefruit juice may cause a slight delay in the absorption of thyroid hormone medication (3) . And if you drink coffee, this also can decrease the intestinal absorption of thyroxine (4) .
So just to make it easier to read, I’ll list the foods which can decrease the absorption of thyroid hormone medication below:
Calcium fortified juices
Nutrients Which Can Affect The Absorption of Thyroid Hormone Medication:
Calcium. Numerous studies show that calcium supplementation can decrease the absorption of levothyroxine. Most of these studies involve calcium carbonate (5)  (6)  (7) , although another study showed that calcium citrate and calcium acetate can also decrease its absorption (8) . And so if you are taking any type of thyroid hormone medication it would be a good idea to wait at least 4 hours before taking a calcium supplement.
Chromium. I came across a journal article which demonstrated that chromium picolinate can decrease levothyroxine absorption (11) .
How Long Should You Wait Before Consuming These Foods and Individual Nutrients?
Out of the foods and nutrients I listed here, the main one you need to be cautious about is calcium. If supplementing with calcium, after you take thyroid hormone medication you want to wait at least four hours before taking a calcium supplement. But how about food sources of calcium, such as dairy, or even certain vegetables that are higher in calcium such as broccoli or kale? This isn’t as clear in the research, but it probably is fine to consume foods that are higher in calcium within 30 to 45 minutes of taking thyroid hormone medication, and the same is true with the other foods I mentioned. With regards to how long you should wait before consuming these other individual nutrients I mentioned, such as iron and fiber, the research isn’t as clear. Just to play it safe it probably would be best to wait at least a couple of hours before taking an iron or fiber supplement after taking thyroid hormone, although some sources claim to avoid taking iron or fiber supplements within four hours of taking thyroid hormone medication.
Drugs That Can Interact With Thyroid Hormone Medication
Many commonly used drugs, such as bile acid sequestrants, sucralfate, aluminium-containing antacids, phosphate binders, raloxifene and proton-pump inhibitors, have also been shown to interfere with the absorption of levothyroxine (14) . Estrogen therapy can also interfere with the absorption of levothyroxine (15)  (16) . And so if you are taking any of these medications it is best to speak with your medical doctor to find out how long you should wait to take them after you take thyroid hormone medication.
So hopefully you have a better understanding of some of the foods, nutrients, and drugs that can interfere with thyroid hormone absorption. Soy, walnuts, calcium-fortified juices, grapefruit juices, and coffee can decrease the absorption of thyroid hormone. Some of the nutrients which can interfere with the absorption include calcium, iron, chromium and fiber. And numerous medications can interfere with the absorption of levothyroxine, including bile acid sequestrants, sucralfate, aluminium-containing antacids, phosphate binders, raloxifene, proton-pump inhibitors, as well as estrogen therapy.