9 Causes of Hypothyroidism

Did you know that there are 9 possible causes of hypothyroidism?  

Years ago, when I first asked my doctor “why is my thyroid underactive?” the answer was “we don’t really know, here is your script”.  Since then we have come a long way in understanding the many causes of hypothyroidism, and what you can do about it. 

reasons for hypothyroidism

Don’t want to read the post?  Then simply watch the video to find out more about the causes of hypothyroidism:

There are 9 possible causes of hypothyroidism (that we currently know of).  One or more of these could the reason that you are struggling with annoying or even debilitating symptoms of an underactive thyroid.

When you find the root causes, you can then take action to address it, and in doing so, your symptoms should reduce or even go away completely.  

You will need to work with your doctor to investigate all these options. 

#1 Pituitary gland disfunction

The first reason is not a thyroid problem, but a problem with the pituitary gland in the brain.  The pituitary gland is called the master gland, as it managed so many different hormones in the body.

This little gland sends out a hormone called TSH (thyroid-stimulating hormone) which tells the thyroid gland how many thyroid hormones to make.  

When there is a problem with the pituitary gland, the TSH hormone may be impacted, and too much or too little TSH may be sent to the thyroid gland.  As the thyroid gland is taking its instructions from TSH, it can then impact thyroid hormone production. 

What could impact the function of the pituitary gland? 

  • infection
  • blood sugar imbalances
  • insulin resistance
  • chronic stress.

#2 Conversion problem of T4 to T3

The thyroid gland produces mostly T4 hormones (which are the inactive form of thyroid hormones) and a few T3 hormones (which are the active form of thyroid hormones).  

The body needs to convert the T4 hormones to the T3 hormones for the body to use it.  This conversion occurs in a few places in the body, including the gut, liver, heart, muscles, and nerves.  Most of the conversion happens in the liver, with about 20% of the conversion occurring in the gut.

There are a few causes that may impact the conversion process:

  • sluggish liver or liver disease
  • inflammation
  • little healthy gut bacteria
  • high cortisol levels
  • heavy metal toxicity (which impacts liver function)
  • high estrogen levels
  • radiation therapy
  • surgery
  • diabetes
  • aging.

#3 Too little or too much TBG in your blood

The thyroid hormones hitch a ride on a protein in your blood as it moves through your body.  This protein is called TBG (thyroid-binding globulin).   While it is attached to TBG, it is not available for your cells to use.

When you have too much TBG in your blood, it means that too much of your thyroid hormones are not available.  

TBG can be elevated when estrogen levels are too high, which is often associated with birth control pills or estrogen replacement therapy.  

Too little TBG can also be a problem, as there is now not enough TBG available to transport the thyroid hormones through the body.   It can also result in too much free thyroid hormones in the body, which can cause the cells to become resistant to thyroid hormones – meaning that the cells are not allowing thyroid hormones into the cells anymore. 

In women, high testosterone levels (commonly associated with PCOS and insulin resistance), could lead to low TBG levels. 

#4 Autoimmune disease Hashimoto's Thyroiditis

One of the most common causes of hypothyroidism is the autoimmune disease Hashimoto’s Thyroiditis. 

Hashimoto’s Thyroiditis is when the immune system produces antibodies to fight and destroy invaders, such as viruses, bacteria, toxins, and other pathogens.  It may happen that your immune system attacks and destroys a part of your own body, which is called an autoimmune disease.

When your immune system attacks and destroys your thyroid gland, cells of your thyroid gland are destroyed. This condition is called Hashimoto’s Thyroiditis. Over time, your thyroid gland cannot produce the number of thyroid hormones anymore that your body needs. 


READ MORE: The Ultimate Guide to Hashimoto’s Thyroiditis


#5 Overactive thyroid or Graves Disease

It is strange to think that an overactive thyroid can lead to an underactive thyroid.  An overactive thyroid, which is also called Graves Disease, can lead to serious health issues, and so doctors have to reduce the thyroid hormone levels.

The two options that doctors recommend is to treat it with radioactive iodine, or surgically remove a part of your thyroid gland. 

When you take radioactive iodine, you literally destroy your thyroid gland.  Now you will need to take thyroid hormones for the rest of your life.

When a portion of your thyroid gland is removed, it may lead to thyroid hormone levels that are now too low, and you will need to take thyroid hormones.  

#6 Removal of the thyroid gland

There may be valid reasons to remove the thyroid gland, including thyroid cancer. Since there is no thyroid gland anymore to produce thyroid hormones, you will need to take thyroid hormones.  

#7 Medications

Some medications may interfere with thyroid hormone production or delivery, including lithium (which is used to treat certain phyciatric disorders), radiation and chemotherapy.  

# 8 Pregnancy

Some women may develop hypothyroidism during or after pregnancy.  

Hypothyroidism during pregnancy increases the risk of miscarriage, premature delivery, and preeclampsia (higher blood pressure in the last three months of pregnancy). It can also impact the development of foetus. 

#9 Iodine deficiency

The thyroid gland needs iodine to make thyroid hormones, so it may seem logical to take an iodine supplement to help support thyroid hormone production.

The problem is that the range of iodine needed is very small, and it is very easy to take too much iodine.   

Supplementing with iodine is controversial in the medical field. If you have an underactive thyroid due to the autoimmune disease Hashimoto’s, you may increase your symptoms when you take additional iodine.  It’s like pouring oil on a fire!  

Too little iodine is also a problem, as now your thyroid gland cannot make enough thyroid hormones. 

Before you start supplementing with iodine, please speak with your doctor to test your iodine levels first.

In closing

There are currently 9 causes of hypothyroidism that we know of.  I believe it is worth the effort to figure out why your thyroid is underactive. And keep in mind, you may be dealing with more than one reason.  

For example, you may have the autoimmune condition Hashimoto’s Thyroiditis, but you could also have high testosterone levels and heavy metal toxicity.  

You may need to put on your detective had, and with your doctor, start on a process of elimination to figure out your underlying cause.  Once you know what is causing your underactive thyroid, you can take action to address it. 


  1. Hashimoto’s Thyroiditis: A practical guide for the newly diagnosed to reduce your symptoms, increase your energy and redeem your life Adele du Rand. 2021, pages 52-55.
  2. Metabolism of Thyroid Hormone.  NIH. Peeters R.P et al.  https://www.ncbi.nlm.nih.gov/books/NBK285545/
  3. What you should know about iodine deficiency.  Cirino E, Healthline.  https://www.healthline.com/health/iodine-deficiency#diagnosis.  Accessed 2 June 2022
Adele du Rand

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