Lots of Things Impact Thyroid Hormone Absorption

Hey people,

I had a question recently from someone asking what foods can hamper thyroid hormone absorption. This is an important question, so I thought I’d take this opportunity to answer it.

How Hormones Bind

The first thing to understand about thyroid hormone is that it behaves a little differently than many of it’s hormone cousins and binds quite easily to stuff.

Let me break it down for you:

The ability of a hormone to bind to a receptor inside or outside a cell depends on the chemical makeup of that hormone and how compatible it is to the cell’s fatty outer membrane.

Some hormones can go easily into cells to find receptors. For example, fat based steroid hormones like estrogen, progestins, etc. belong to this category. They prefer fatty surroundings (fat or lipid soluble) and they don’t like water.

As a result they can pass easily through the cell membrane, but they need proteins to help them through the watery bloodstream (these are the binding globulins that you may have heard of).

Receptors for these steroid hormones are found in several different places: the cells outer membrane, the cytoplasm and/or the nucleus inside the cell.

Other hormones stay outside the cell and attach to receptors found in the outer membrane. Insulin, growth hormone and other protein based peptide hormones prefer water (water soluble) and don’t like fat (fat insoluble).

The cell’s fatty membrane makes it difficult for these messengers to enter the cell. This keeps these peptide hormones outside the cell where they only bind with receptors found there.

Thyroid Hormone Is Unique

Thyroid hormones, which are derived from amino acids, behave more like steroids than its peptide cousins and can actually bind to receptors both inside and outside the cell.

Which means they are very adaptable and flexible and it can also mean that they are able to bind to other things as well, like food, chemicals and minerals.

Many Drugs and Supplements Bind to Thyroid Hormone

Many commonly used medications or supplements like iron, calcium, estrogen, proton pump inhibitors, and statins can cause affect thyroid hormone absorption or binding to plasma proteins.

Sometimes, if the doctor is paying attention, this may require making changes in dosage of levothyroxine. If you have been prescribed any of these drugs with your thyroid medication, you need to be aware of this.


Alcohol can disrupt thyroid function in a number of different ways. There are some indications that it may lower peripheral T4 and T3 levels.

In addition, it has a toxic effect on thyroid cells and ethanol is actually used to treat thyroid nodules in some cases. It can also, potentially, reduce the risk of certain types of thyroid cancer.

On the flip side, alcohol is very hard on the digestive tract and can also lead to destruction of the gut lining and make leaky gut worse.

I generally recommend avoiding alcohol, especially if you are trying to heal the gut.

Coffee and Tea

Coffee also impacts the absorption of levothyroxine; this is why thyroid patients need to take their hormone replacement pill at least an hour before drinking coffee.

Caffeine found in coffee can also increase blood sugar levels . This is especially bad for people with hypoglycemia (or low sugar levels) because it can lead to complications.

For example, blood sugar fluctuations can cause cortisol spikes, which not only exhaust the adrenals, but also can wreak havoc on the immune system. Obviously, this is not a good thing for those of us with adrenal fatigue, and/or Hashimoto’s.

I recommend avoiding coffee if you have adrenal issues or hypoglycemia.

Black and green tea also has caffeine (though in lesser amounts than coffee), and it contains tannins which can hamper iron absorption and many teas also contain fluoride which blocks iodine absorption and may hamper thyroid function.

Green and Black tea are also Th2 stimulants. Drinking it in moderation may be ok for some and not good for others. If you drink a lot of tea, you may want to eliminate it for a period of time to see if it has an impact on your symptoms.

High doses of green tea have also been found to cause a significant decrease in serum T3 and T4 and increase in TSH levels has been reported along with decreased TPO and deiodinase activity in response to dietary green tea extract in rats.


There is ample evidence that gluten can lead to poor absorption of thyroid hormone. This is true for a couple of reasons; it can lead to destruction of the intestinal lining (which can hamper absorption), and it can cause systemic inflammation (which can clog receptors) This can lead to hypothyroidism and/or poor results from medication.

If you follow this page, you know I recommend eliminating gluten 100%. (For an in depth look at this read this post.)


Lactose has also been found to hamper thyroid hormone absorption. And casein, a protein found in milk is similar in protein structure to gluten and can also cause gluten like problems.

I also recommend eliminating dairy 100%. (Grass fed butter is one possible exception) (For an in depth look at this read this post.)


Soy is rich in phytoestrogens and affect levels of thyroid binding globulin (creating more of it). It can also hamper thyroid hormone absorption. Soy can also be goitrogenic in large quantities.

Soy protein and isoflavones doesn’t seem to harm people with sufficient levels of iodine, but it still may interfere with absorption of thyroid medication.

I generally recommend avoiding soy with the occasional exception of miso and fermented soy products like tempeh.


As mentioned above, the adrenals release cortisol to compensate for low blood sugar levels.

Cortisol directly inhibits the enzyme (5’-deiodinase) which converts inactive T4 into active T3.  This can lead to low T3 levels.

In addition, elevated cortisol will cause thyroid hormone receptor insensitivity meaning that even if T3 levels are high enough, they may not be able to bind normally to receptor sites. And when this happens it doesn’t get into the cells.

Cortisol will also increase the production of reverse T3 (rT3) which is inactive. (It’s kind of like the anti-hormone.)

rT3 can cause an increase in the production of substances known as thyronamines that can cause hypothyroid symptoms (like, low basal body temperature,fatigue, depression, etc.) along with insulin resistance symptoms of increased blood sugar.

Cortisol can also lower the levels of protein that binds to thyroid hormone so it can circulate in a stable structure.

And finally, elevated cortisol will slow TSH production by messing with hypothalamic-pituitary feedback leading to lower TSH production.

Sugar should be treated as the addictive drug that it is. Use with extreme caution.

Processed Foods

Processed foods tend to be high in both sodium, sugar and saturated fat. High sodium levels have been linked to autoimmunity and to thyroid disease. Sodium is important for getting iodide into thyroid cells.

Excess amounts of sodium can lead to higher amounts of iodine in the thyroid which can lead to a more aggressive autoimmune attack.

We have already discussed problems caused by low sugar. High blood sugar levels can lead to insulin resistance. This can also cause a reduced conversion of T4 to T3 hormones.

Eat real whole food. Processed food has little or no nutritional benefit. Don’t eat it.


Diets high in polyunsaturated fat caused significant thyroid dysfunction in rats. High triglycerides, decreased total T4 and free T4 levels and elevated TSH were all noted.


Naturally Found in found in legumes, plants, amiodarone, lithium, as well as cabbage, cauliflower, broccoli, turnip, forms of root cassava. These may reduce T4 absorption if iodine and/or selenium levels are low.

Generally, I think these foods have so many health benefits that they should be eaten. Goitrin is an active goitrogen present in plants of Rutabaga, turnip and Brassicae seeds.

Steam or blanch the vegetables as cooking destroys the enzyme responsible for activation of progoitrin to goitrin thus negating its anti-thyroid effects.

So, eat these vegetables, but don’t eat wheel barrels’ full. Normal moderate amounts are fine, in my opinion.


This common gluten free ingredient contains C-glycosylflavones which may inhibit TPO activity. Be cautious with millet. In moderate amounts it is probably ok.

Environmental Toxins

Pesticides can lead to decreased half life of T4.

BPA (bisphenol-A) has been found to be an endocrine disruptor and may have direct action on thyroid receptors.

Percolates found in rocket fuel, thiocyanates and nitrates interfere with iodine uptake. A study in California on pregnant women found a strong association between urinary percolate levels and decreased total and free T4 and increased TSH.

Heavy metals like cadmium and lead are also known to affect thyroid function. In a study on pregnant women, those from lead exposed town had lower mean free thyroxine (FT4), higher mean TPO antibodies along with higher lead concentration suggesting stimulation of auto-immunity by prolonged lead exposure.

Bottom Line:

As you can see, there are many things that can bind to thyroid hormone both natural and chemical. All must be considered when deciding on dosage and when trying to improve thyroid hormone function in the body.


https://www.ncbi.nlm.nih.gov/pubmed/25040647 Drugs and thyroid hormone interactions

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3743356/ Alcohol and the thyroid axis

https://www.ncbi.nlm.nih.gov/pubmed/9846599 Affects of caffeine on glucose levels

http://www.thyroid.org/patient-thyroid-information/ct-for-patients/vol-5-issue-6/vol-5-issue-6-p-3-4/ Gluten, celiac and thyroid hormone absorption.


https://www.ncbi.nlm.nih.gov/pubmed/16571087 Soy and Thyroid hormone absorption

https://www.ncbi.nlm.nih.gov/pubmed/15642784 Sodium and thyroid hormone

https://www.ncbi.nlm.nih.gov/pubmed/20561943 Green tea and thyroid function

in rats

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4220075/ Fat and rats

https://www.ncbi.nlm.nih.gov/pubmed/26485730 California Percolate study

https://www.ncbi.nlm.nih.gov/pubmed/24866691 Lead exposure and thyroid function

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4740614/#b52 Possible Toxicants Involved in thyroid dysfunction

About the Author Marc Ryan

So now, not only is it my profession, it’s my passion, and it’s personal. I’ve been joking with people lately saying it’s a blessing and a curse. A blessing because I really get it, and a curse because I really got it! ?

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