Why is my thyroid underactive?

Do you know why your thyroid is underactive?  There are actually a few reasons why your thyroid is not working like it is supposed to, and today I want to share it with you. Once you know why your thyroid is underactive, you can take control of your health.  Depending on the underlying cause, you can make changes to your lifestyle and diet to support your thyroid function.


It is too easy for many doctors to just diagnose the underactive thyroid and then prescribe hormones (usually synthetic T4 hormones) to replace the hormones that your thyroid cannot produce anymore.  But few doctors will investigate the reason for the lack of thyroid hormones. Why?  Probably because the standard of care is exactly the same regardless of the diagnosis: prescribe synthetic T4 hormones to replace the missing hormones.  So why go through all the hassle of finding out the root cause?


Here is why I believe you absolutely need to know why your thyroid is underactive.   In many instances, once you know the root cause of underactivity, you can make changes to medication, lifestyle and diet which can positively impact the thyroid. 


I have identified nine possible reasons:


  1. The immune system
  2. Hyperthyroidism or Grave’s Disease
  3. Removal of the thyroid gland
  4. Iodine deficiency
  5. Medications and certain therapies
  6. Pregnancy
  7. Too little or too much TGB in your blood
  8. Pituitary gland dysfunction
  9. Your body cannot convert inactive T4 to active T3.

1.  The Immune System

The body’s immune system produces antibodies to attack foreign invaders and to fight off viruses and bacteria. With inflammation, the antibodies then also attack a part of the body in a case of mistaken identity, causing what is called an autoimmune reaction. Hashimoto’s Thyroiditis is a situation in which the immune system is attacking the thyroid gland, and over time, the thyroid cells are damaged and not able to produce thyroid hormones any longer.


To diagnose Hashimoto’s Thyroiditis, your doctor will have to request a thyroid panel including two antibody tests, namely TPO (thyroid peroxidase antibodies) and TgAB (thyroglobulin antibodies).  When these antibodies are present, you likely have Hashimoto’s Thyroiditis. Interestingly, you may still have Hashimoto’s Thyroiditis and it may not show in the antibody tests. If you tested negative, it may be worthwhile to wait a few weeks and test again.


Once you know that you have Hashimoto’s Thyroiditis, you can make changes to your diet and lifestyle to calm the immune system so that it doesn’t destroy your thyroid further.  Of course, depending on the condition of the thyroid gland, you may need to take thyroid hormones to replace the hormones that your thyroid cannot produce anymore.


2.  Hyperthyroidism or Grave’s Disease

It is strange to think that a case of an overactive thyroid can lead to an underactive thyroid. People who have too high a level of thyroid hormone (called hyperthyroidism) are often treated with radioactive iodine or anti-thyroid medication to limit the production of thyroid hormones. Sometimes these treatments can lead to lowering the thyroid production too much, resulting in permanent hypothyroidism.


3.  Removal of the thyroid gland

Removing a part of the thyroid gland can reduce thyroid hormone production, and in some cases, removal of the thyroid gland is required, which will leave a need to replace all the thyroid hormones with medical treatment.

4.  Iodine deficiency or surplus

Iodine is a trace mineral that is found in iodized salt, seafood, seaweed, and plants that grow in iodine-rich soil. Iodine is only used by the thyroid gland, and you only need a very little amount of it.  The body cannot make iodine on its own, so you have to get it through food.


When there is too little iodine available, the thyroid gland cannot produce the number of thyroid hormones the body needs.  Therefore, your thyroid becomes underactive.  


For most people, however, a lack of iodine is not the problem.  It is too much iodine that creates a problem.  The Western diet typically provides too much iodine to the body.  Several small studies have indicated that too much iodine can decrease the release of thyroid hormones by the thyroid gland.  And then there has been instances where too much iodine has caused the thyroid gland to produce too much thyroid hormones, leading to hyperthyroidism!  By the way, this has a name: the Jod-Basedow phenomenon and it was first observed in the early 1800’s. 


You can do urine and blood tests for iodine levels. Speak with your doctor if you want to get it tested.  I think that most of us on a Western diet probably have too much iodine, and would benefit from a low iodine diet.  The problem is that iodine levels in food is very difficult to measure, so the focus would be to reduce the food that is obviously high in iodine, like iodized salt, bread and baked products, seafood and sea veggies, dairy and egg yolks.

5.  Medications and certain therapies

Certain medications can lead to an underactive thyroid, for example, lithium (used to treat certain psychiatric disorders). Radiation and chemotherapy to treat certain cancers can impact the ability of the thyroid gland to produce thyroid hormones.


These treatments are life-saving, so if it is the root cause of your underactive thyroid, please consult with your doctor to ensure you replace the thyroid hormones that your body needs.

6.  Pregnancy

Some women can develop hypothyroidism during or after pregnancy. This can be a problem, as hypothyroidism in pregnancy can increase the risk of miscarriage, premature delivery and preeclampsia (characterized by higher blood pressure in the last three months of pregnancy). It can also impact the development of the fetus.


Again, if you think your thyroid may be underactive, please consult with your doctor.


Image credit: 2626886© Judy Ben Joud | com

7.  Too little or too much TGB in your blood

Thyroid hormones hitch a ride on the protein TBG (thyroid-binding globulin) in your blood, and while the thyroid hormones are attached to TBG, it’s not available to the cells. When TBG is too high or too low, it can cause problems:

  • TBG can be elevated due to high estrogen levels, which are often associated with birth control pills or estrogen replacement. With high levels of TBG, the levels of free thyroid hormones will be low. Elevated estrogen creates too many TBG’s (thyroid-binding globulin) so that the thyroid hormones cannot get into the cells
  • TBG can be low due to high testosterone levels. In women, this is commonly associated with PCOS (polycystic ovary syndrome) and insulin resistance. But with low TBG, the levels of free thyroid hormones will be high, which is surely good, right? Unfortunately, not. Too many free thyroid hormones can cause the cells to develop resistance to the hormones, and then the cells can’t use them.

If you suspect this could be the root cause, speak with your doctor about doing a serum TBG level test in conjunction with estrogen and testosterone levels.  You can then work with your doctor to address the underlying cause.


8.  Pituitary Gland Dysfunction

The pituitary gland is located in the brain and is responsible for managing a range of hormones. There are several reasons why the pituitary gland may not function as well as it should. The pituitary gland is responsible for sending the hormone TSH (thyroid-stimulating hormone) to the thyroid gland. If the pituitary gland is not working well, TSH to the thyroid might be impacted, and the thyroid doesn’t produce enough T4 and T3.


There are a few things that can impact the function of the pituitary gland function, including infection, blood sugar imbalances, chronic stress, pregnancy, hypoglycemia, or insulin resistance.


Testing for pituitary disfunction is a little more complicated and may include blood tests and MRI and CT scans.  Speak with your doctor about the process and tests.


9.  Your body cannot convert inactive T4 to active T3

Your body needs to convert T4 to T3 for the cells to be able to use it. You may have enough hormones, but it is not being made available to the cells. This is technically not a thyroid gland problem, but a problem elsewhere in the body that is affecting the thyroid system.


There are several reasons why this may occur, such as inflammation, high cortisol levels, a sluggish liver or liver disease, high estrogen level, heavy metal toxicity, aging, diabetes, surgery, radiation, or too little healthy gut bacteria.


To figure this one out, you may need to go on a trial-and-error journey with your doctor to figure out what the issue is, such as check for liver function, heavy metals toxicity, diabetes and estrogen levels.  You can also make lifestyle and dietary changes to help your gut function at its best levels!


In closing

Next time you are seeing your doctor, ask him or her about why your thyroid is underactive and if you can do anything about it.  If your doctor brushes you off, I recommend you find a functional medicine doctor who is willing to work with you to find the root cause and then what you can do to improve your health.