Thyroid Hormone Levels and Your Genes

The thyroid is a master regulator of many of your body’s systems. It is integrally involved in metabolism and helps maintain body temperature, heart rate, breathing, and body weight. [ref]

Your genes play a big role in how well your thyroid works and how your body produces and converts the different forms of thyroid hormone. This article digs into the science of how the thyroid works and the genetic variants that shape your thyroid function.

Thyroid Problems and Genetics

Thyroid hormone levels play a vital role in how you feel and in your overall health and wellbeing. A lot of people think of thyroid in terms of metabolism and weight, but your thyroid hormones also affect your body temperature, gut health, muscle energy, heart rate, skin health, bone health, and more.

In 2016, the #1 prescribed drug in the US was Synthroid, a synthetic thyroid hormone with 123 million people on the drug.[ref] That is a huge number of people having problems with their thyroid!

Your body needs the right amount of the thyroid hormones, and at the right time. Hypothyroidism is caused by too little thyroid hormone; hyperthyroidism is caused by too much thyroid hormone.

If you have thyroid problems, learning which genetic variants you carry may be a way to shed some light on what is going on with your thyroid. Knowing where your genetic susceptibilities lie can help you figure out (along with your doctor) the best way to solve the problem.

How does your thyroid work?

This system all starts in the brain, instead of the thyroid. The rate at which the thyroid gland produces and releases thyroid hormone is controlled by the hypothalamus, a region in the brain, and the pituitary gland.

The hypothalamus releases thyrotropin-releasing hormone (TRH) which is a signal to the pituitary to create and release thyroid-stimulating hormone (TSH). The TSH hormone then travels to the thyroid gland to signal for the production of thyroxine (T4) and triiodothyronine (T3).

The thyroid gland is located in the neck and excretes two hormones: thyroxine (T4) and triiodothyronine (T3). Both of these hormones contain iodine molecules in them, which makes iodine essential for thyroid function. Within the thyroid gland, there are specific transporters to move iodine (in the form of iodide) into the follicular cells where the T3 and T4 are produced.

The balance of the two types of thyroid hormone (T4 and T3) is important. T3 is the active form of the thyroid hormone that your body uses, and T4 is the inactive form that can be converted into T3 when needed in your cells.

The thyroid gland produces and releases more T4 than T3 (around 80% is T4), but enzymes can convert T4 to T3 in your tissues and organs. Too much of the active T3 in cells will cause enzymes to inactivate it to reverse T3 (rT3).[ref]

Thyroid hormone levels are an intricate balance between the production of T4, conversion to T3, inactivation to rT3, TSH levels, and the feedback loops controlling TRH and TSH.

What exactly does thyroid hormone do in a cell?

Let’s take this explanation one step further and look at how the thyroid hormone (mainly T3) actually makes something happen within your body.

Within cells, the thyroid hormone crosses into the nucleus and binds to a thyroid hormone receptor. These receptors then control the transcription of specific genes. Basically, they turn on a gene so that whatever protein that gene codes for gets made. [ref]

In different cell types, the thyroid hormone receptors are going to control the production of different proteins. For example, T3 can enter the cell nucleus and bind to the thyroid hormone receptor that controls the transcription (and production) of fatty acids in the liver (de novo lipogenesis). Thyroid hormone receptors also regulate the production of mitochondria (the powerhouse of the cell) and the transcription of some genes within the mitochondria.[ref]

Going just a little deeper here, the thyroid hormone receptors in the cell nucleus don’t act alone. They are often bound with a retinoic acid receptor, which is activated by vitamin A. The thyroid hormone receptors also need zinc in the way that they bind to the DNA. This makes it important to have adequate vitamin A and zinc levels – along with enough thyroid hormone being produced. [ref]

Finally, let me throw in that there are actually two different thyroid hormone receptors – THR-alpha and THR-beta. While both are located in most types of cells, THR-beta is the major form in the liver and THR-alpha is the major form in the heart cells and the bone. [ref]

Genes that impact thyroid hormone levels:

All of this comes down to genetics at a basic level — the creation of thyroid hormones, conversion of hormones, and the receptors for the hormones are all coded for by genes. And those genes can have genetic variations that alter their function.

Thyroid Stimulating Hormone (TSH) related genes:

The first thing that most doctors check on a blood test is the TSH (thyroid-stimulating hormone) level.  A person can be naturally slightly higher or lower than average for TSH levels based on their genes.   An interesting study published in the journal of the European Society of Endocrinology looked at the heritability of thyroid hormone levels in men who had no thyroid auto-immune disease or dysfunction and found several SNPs that were responsible for approximately 50 – 90% of thyroid hormone variability. Thus TSH levels naturally vary a bit from person to person.

The TSHR gene (thyroid-stimulating hormone receptor) codes for a receptor protein that controls thyroid cell metabolism [ref] TSH levels are tied to genetic variations of the TSHR gene.

Check your genetic data for rs1991517 D727E (23andMe v.4; AncestryDNA):

  • C/C: typical
  • C/G: slightly lower TSH, increased risk of hypothyroidism and goiter
  • G/G: lower TSH, increased risk of hypothyroidism and goiter [ref][ref]

Check your genetic data for rs121908866 (23andMe v4;AncestryDNA);

  • A/A: congenital hypothyroidism
  • A/G: risk of congenital hypothyroidism [ref]
  • G/G: typical

Check your genetic data for rs121908867 (AncestryDNA);

  • C/T: risk of congenital hypothyroidism [ref]
  • C/C: typical

The PDE8B gene codes for a protein that causes the inactivation of cyclic AMP (important in energy regulation) in the thyroid. PDE8B genetic variants have been repeatedly associated with TSH levels, specifically in those of European descent. [ref]

Check your genetic data for rs4704397 (23andMe v.4, v.5; AncestryDNA):

  • A/A: increase of approx. 0.26 – 0.29 uIU/ml in serum TSH [ref][ref]
  • A/G: increase of ~0.13 uIU/ml in serum TSH
  • G/G: typical

Check your genetic data for rs6885099 (23andMe v.4, v.5; AncestryDNA)

  • A/A: decreased TSH [ref]
  • A/G: slightly decreased TSH
  • G/G: typical

The FOXE1 gene (thyroid-specific forkhead transcription factor) has also been identified to increase the risk of primary hypothyroidism[ref] and with changes in TSH levels.

Check your genetic data for rs7850258 (23andMe v.4, v.5; AncestryDNA):

  • A/A: Lower odds of hypothyroidism (OR = 0.74)  [ref]
  • A/G: typical odds of hypothyroidism
  • G/G: typical (most common genotype)

Check your genetic data for rs965513 (23andMe v.4, v.5, AncestryDNA):

  • A/A: decreased TSH, increased risk of thyroid cancer [ref]
  • A/G: decreased TSH
  • G/G: typical

Autoimmune Thyroid – Graves’ and Hashimoto’s

Graves’ disease is an autoimmune condition that affects about 1% of the population and causes hyperthyroidism. In Graves’ disease, the body produces antibodies against TSHR.

A 2012 study published in the Endocrine Journal showed that there are several SNPs in the TSHR gene that influence the risk of the autoimmune thyroid diseases (AITD), which includes Graves’ disease and Hashimoto’s thyroiditis.  The study states that “genetic factors confer 80% contribution to the etiology of AITD”.[ref]  Note that this does not mean that 80% of people with the SNPs have Graves’ or Hashimoto’s. The prevalence of Hashimoto’s in Caucasian women is between 1 and 2% and is even less in men. [ref]

It is thought that one of the reasons that TSHR genetic variants are a risk factor for Graves’ is because the changes in the TSHR gene could cause a slightly different structure for the receptor protein and possibly “exacerbate autoimmune response against TSHR in” Graves’ disease. [ref]

Check your genetic data for rs3783938 ( 23andMe v.4, AncestryDNA):

  • T/T: higher frequency of Hashimoto’s (OR 1.4)
  • C/T: higher frequency of Hashimoto’s
  • C/C: typical

Check your genetic data for rs12101255 ( 23andMe v.4, AncestryDNA):

  • T/T: higher frequency of Graves’ disease (OR 1.4 – 1.8) [ref]  (very common genotype)
  • C/T: higher frequency of Graves’ disease
  • C/C: typical

Check your genetic results for rs179247 (23andMe v4, AncestryDNA):

  • A/A: increased risk of Graves’ disease (OR 1.4 – 1.8) [ref] (very common genotype)
  • A/G: typical
  • G/G: typical

TPO Gene: Thyroid peroxidase (TPO) antibodies are a marker of autoimmune thyroid disease. Several genetic variants in the TPO gene are associated with an increased risk of autoimmune thyroid disease.

Check your genetic data for rs2071403 (23andMe v5; AncestryDNA.)

  • G/G: Most common genotype – increased risk of Graves and Hashimoto’s [ref]
  • A/G: no increased risk
  • A/A: no increased risk

The PTPN22 gene is associated with an increased risk of many autoimmune diseases, including Hashimoto’s.

Check your genetic data for rs2476601 (23andMe v4; AncestryDNA):

  • G/G: typical
  • A/G: slight increase in the risk of autoimmune thyroid disease
  • A/A: slight increase (OR 1.36)  in the risk of autoimmune thyroid disease [ref]

DIO1, DIO2 – conversion of storage (T4) to active (T3)

DIO1 & DIO2 genes: The deiodinase 1 (DIO1) gene encodes a protein that converts T4 to T3 and is involved in the degradation of both T3 and T4 in the liver, kidney, thyroid, and pituitary gland.  Iodine and selenium are involved in these reactions.[ref]  DIO2 is also involved in the conversion of T4 to T3, mainly in the skeletal muscles, central nervous system, pituitary, thyroid, heart, and brown fat.[ref]

Check your genetic data for rs2235544 (23andMe v4, v5; AncestryDNA):

  • A/A: less active DIO1 – decreased free T3, a larger decrease in T3 due to organochloride pesticides [ref][ref][ref]
  • A/C: intermediate (most common genotype in many populations)
  • C/C: more active DIO1enzyme – decreased free T4, increased fT3 (better ratio) [ref][ref]

Check your genetic data for rs11206244 (23andMe v4, v5; AncestryDNA):

  • T/T: higher rT3, lower free T3, higher fT4  [ref][ref]
  • C/T: lower T3
  • C/C: typical

Check your genetic data for rs225014 (23andMe v.4; AncestryDNA):

  • C/C: decreased DIO2 enzyme (T4 to T3 conversion)  [ref] associated with improved wellbeing on combo T4 + T3 therapy vs T4 alone [ref]
  • C/T: decreased  conversion of T4 to T3
  • T/T: typical; less likely to get Hashimoto’s or Graves’ [ref]


Rare causes of thyroid disease:

THRB & THRA genes: The thyroid hormone receptor genes code for the receptor that the thyroid hormone binds to in the nucleus of the cell. Mutations in these genes (rare!) cause thyroid hormone resistance.  Generally, THRB or THRA mutations will cause hypothyroidism that is recognized and diagnosed in infants or children.[ref] In other words, mutations cause more severe symptoms that affect growth and development.

Check your genetic data for rs28933408 (23andMe v4):

  • G/T: thyroid hormone resistance  [ref]
  • G/G: typical

Check your genetic data for rs137853162 (AncestryDNA only)

  • G/T: thyroid hormone resistance  [ref]
  • G/G: typical

SERPINA7 gene: codes for the thyroxine-binding globulin protein

Check your genetic data for rs28933689 (23andMe v4 only):

  • G/T: Thyroxine-binding globulin deficiency [ref]
  • G/G: typical

Check your genetic data for rs2234036 (23andMe v4 only):

  • A/G: Thyroxine-binding globulin deficiency [ref]
  • G/G: typical



If you are on thyroid medication or under the care of a doctor, please be sure to talk with your doctor about making any changes, including dietary changes, that could affect your thyroid hormone levels.

Selenium is essential to the conversion of T4 to T3.  Brazil nuts are a good source of selenium, and supplements are also available.

Melatonin: The production of melatonin is regulated by TSH. Increasing melatonin increases thyroglobulin. The thyroid gland cells also synthesize melatonin. [ref] You can increase your melatonin levels naturally by blocking blue light at night or synthetically through taking melatonin at night.

Iodine: Make sure you get iodine in your diet – either through seafood, kelp, or iodized salt.

Gluten may be a problem for a few people:  Gluten is often pointed to as a culprit in autoimmune thyroid diseases (Graves and Hashimoto’s).  A 2003 study showed that ~5% of patients with autoimmune thyroiditis also had immune reactions to gluten. [study]  While that isn’t a huge percentage, it may be worth trialing a gluten-free diet if you have an autoimmune thyroid disease. The flip side of that is also worth noting — 95% of people with autoimmune thyroid disease may have no problem with gluten.

Eat your fruits and veggies: The dietary flavonoid kaempferol, found in apples, onions, leeks, grapes, and other fruits and vegetables, induces DIO2 increasing conversion to T3. [study]

Avoid fasting: In studies, fasting and critical illnesses increase the levels of DIO3, which is the enzyme that deactivates thyroid hormone. [study] Fasting (and illness!) may be hard on your supply of active thyroid hormone.

Blocking blue lightLight and circadian rhythms play a role in DIO3 expression as well. [study] Blocking blue light in the evening (from LED bulbs, TV screens, etc) by wearing blue-blocking glasses will help to keep your circadian rhythm on track.

Blame mom: Several recent studies have also pointed to the hereditary epigenetic effects on DIO3 as well. [study]

Myo-inositol For autoimmune thyroid problems, Myo-inositol and selenium have been shown to reduce antibody levels. [study]

Vitamin D supplement has been shown to reduce Hashimoto’s antibody levels. [study]  This is the vitamin D that I use that has coconut oil instead of soybean oil.  (Not saying that anyone should by the brand because I use it — rather that you should make sure that read the ingredients so that you don’t end up with soybean oil or cottonseed oil in your supplement.)

Recent studies on thyroid levels and chemical toxins

With so many people having problems with thyroid hormone levels, the question becomes:  Why now? What is causing this explosion? The foods that we are eating and the fact that we no longer eat the thyroid glands of animals probably plays a role in the hypothyroid epidemic. Additionally, chemicals that are found in nearly everyone’s bloodstream, such as PFOA’s, BPA and phthalates, have been shown in several recent studies to be related to lower thyroid levels.  Study results include:

  • PFAS (Perfluoroalkyl substances in cleaners, insecticides, flame retardants, carpet and fabric stain repellant, and food packaging) affect TSH levels [study]
  • BPA and phthalates (in plastics and register receipts) affect thyroid levels. [study] Read more about how genes play a role in your ability to detox BPA and phthalates.
  • Triclosan (previously used in antibacterial soaps) affects T3 and T4 levels as well as other markers. [study]
  • Depending on your DIO2 genes, organochlorides (in pesticides) may make a significant difference in your thyroid levels. [study]
  • Sucralose (Splenda) also alters thyroid hormone levels by increasing rT3 (a rat study) [study]

Related Genetic Lifehacks Articles:

Primary Hyperoxaluria can cause oxalates to build up in the thyroid gland. [ref] Check your oxalate genes:  Green Smoothie Genes- Oxalates in Your Diet

Toxins such as BPA the phthalates affect your thyroid. Check out the articles on how genes affect your ability to detox BPA and phthalates.

updated and revised 9/10/18

Author Information:   Debbie Moon
Debbie Moon is the founder of Genetic Lifehacks. She holds a Master of Science in Biological Sciences from Clemson University. Debbie is a science communicator who is passionate about explaining evidence-based health information. Her goal with Genetic Lifehacks is to bridge the gap between scientific research and the lay person's ability to utilize that information. To contact Debbie, visit the contact page.