Why is my thyroid underactive?

Have you wondered why your thyroid is underactive?  There are a few reasons that could be the reason why your thyroid is underactive, also known as hypothyroidism.  Knowing the underlying cause is the first step to feeling better.

Pituitary Gland Dysfunction. 

The pituitary gland in the brain is responsible to manage a range of hormones, including sending TSH (thyroid-stimulating hormone) to the thyroid gland.  If the pituitary gland is not working optimally, the TSH to the thyroid gland may be impacted, causing the thyroid to produce fewer hormones.  Cortisol, infection, blood sugar imbalances, chronic stress, pregnancy, insulin resistance, and hypoglycemia are all things that can impact the function of the pituitary gland.


Your body cannot convert T4 to T3. 

Your body may not be able to convert the inactive T4 thyroid hormones into the active T3 thyroid hormones, which is technically not a thyroid-problem, but a conversion problem.  Several factors can affect the conversion, including high cortisol levels, a sluggish liver or liver disease, high estrogen levels, low progesterone levels, or too little gut bacteria.  Certain medications can lead to an underactive thyroid, for example, lithium, radiation therapy, and chemotherapy as it impacts the body’s ability to convert the hormones. 


Part or whole of your thyroid gland was removed. 

If your thyroid was removed, the thyroid hormones in your body will be too low and you will need to take replacement thyroid hormones.

Hyperthyroidism or Graves’ Disease. 

It may feel strange that an overactive thyroid may cause an interactive thyroid!  The treatment for an overactive thyroid is often radioactive iodine or anti-thyroid medication.  Sometimes these treatments lead to much lower thyroid hormone production, resulting in permanent hypothyroidism.


The autoimmune disease Hashimoto’s Thyroiditis. 

The immune system produces antibodies to attack and destroy foreign invaders, viruses, and bacteria.  The immune system also then attacks the thyroid gland and over time, the thyroid cells are damaged and unable to produce thyroid hormones, leading to an underactive thyroid.

Too little or too much TBG in your blood. 

TBG is the protein in the blood that transports the thyroid hormones through the body.  TGB can be too high due to high estrogen levels, and therefore the thyroid hormones that are hitching a ride are not available for the body to use, causing hypothyroidism.  But the other side of the spectrum is not good either.  When TBG is too low, due to high testosterone levels, there are too many thyroid hormones available for the cells to use, and the cells may become resistant to the thyroid hormones and are unable to use the thyroid hormones.

Iodine deficiency

The thyroid gland uses iodine to make thyroid hormones, and an iodine deficiency can lead to hypothyroidism.  The addition of iodine to table salt has eliminated this problem in most of the western world and developed countries.


How you treat your hypothyroidism starts by knowing why it is underactive in the first place.  If you have Hashimoto’s Thyroiditis, it is the immune system that is causing the underactive thyroid, and you will need to calm the immune system else the thyroid gland will continue to be damaged.  Just taking the replacement thyroid hormones is not a treatment, as the issue is not with the thyroid gland.  Only by understanding why your immune system is on overdrive in the first place and addressing that, will you start to feel better and reclaim your health.  




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