Healthy Hormones

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Why is My T4 Low (and What Can I Do About It)?

Do your lab tests show that your T4 level is low?

​​What ​does that mean exactly?

Do you also have symptoms such as fatigue, weight gain, hair loss, constipation, and depression?

If you answered yes, you most likely have ​hypothyroidism which usually causes a low T4 level.

In this article, I will discuss the T4 lab test, what it means when it is low, symptoms that may be associated with a low T4 level, and I will also give some treatment tips that will help raise it to​ an optimal level.

Let’s get started…

​What is T4?

So what is T4 anyway? 

In order to answer that question, we need to talk about the thyroid gland and how it works.

​The thyroid gland primarily produces 2 types of thyroid hormone – Thyroxine (T4) and Triiodothyronine (T3).

The vast majority of the thyroid hormone produced is thyroxine (T4).  Not nearly as much triiodothyronine (T3) is produced.

Both of these hormones are produced ​in response to a hormone secreted by the pituitary gland called Thyroid Stimulating Hormone (TSH).

​The association of TSH and T4 gives us valuable information about how well the thyroid gland is working. That is why these tests should always be tested together.

​So what is the purpose of T4 in the body?

T4 is not nearly as biologically active as T3, but it still helps regulate how much T3 is available in the body.  ​

Most of the T3 in the body is actually produced from peripheral conversion of T4.  

​More specifically, as the body needs T3, an enzyme called a deiodinase will cleave off an iodine molecule from T4 which converts it into T3.

You can therefore think of T4 as a storage reservoir for the body to use to make T3 as it needs it.  This is the primary purpose of T4.

Causes of Low T4

​So what happens if the T4 level is low?

If the reservoir of T4 becomes low in the body (sort of ​like most of the lakes in the Texas Panhandle where I live), then there is not enough substrate that the body can use to produce T3.

The T3 levels then ​also drop, and symptoms of hypothyroidism develop.

​Why does the T4 level drop?

Let’s discuss the most common causes:

​1.  Autoimmune Thyroiditis (Hashimoto’s) –

​There are many theories about how and why autoimmune disorders ​develop.

​It is generally accepted that 3 things must be in place for an autoimmune disorder to develop.

  • Genetic Predisposition – You have a variation in one of your genes that may make it more likely to develop an autoimmune condition.
  • Leaky Gut – The bacterial levels and types of bacteria in your GI tract may be inadequate​.  Also, gaps between the cells in your intestines may widen which allows foreign proteins and toxins to enter the bloodstream that wouldn’t normally get through.
  • Trigger – A physical or emotional event may occur (injury, surgery, major life stress, etc.), or you may be exposed to an environmental toxic of some sort which can damage your immune system and cause it to ​function improperly.

​A common theory is that some of these foreign proteins that enter our bloodstream look similar to proteins in our body.  As a result, ​as our immune system makes antibodies against these foreign proteins, it in effect also ​unintentionally makes antibodies against parts of our body.

This is called molecular mimicry.

​This appears to be what happens in Hashimoto’s Thyroiditis.

The result is these auto-antibodies continuously attack parts of our thyroid gland, ​gradually destroying it.

As the cells of the thyroid gland are destroyed, its ability to produce thyroid hormone is impaired and hypothyroidism will develop.

This typically occurs slowly over many years.

Often patients will have classic symptoms of hypothyroidism, but their labs will remain relatively normal until late in the process.

Hashimoto’s is an extremely common condition.  In fact, in my medical practice I typically diagnose one or more people with it every week!  It is by far the most common autoimmune disorder.

Many experts believe that the vast majority (over 90%) of hypothyroidism in the United States is actually caused by Hashimoto’s.

If you have hypothyroidism, you should periodically have your thyroid antibody levels checked.

Click here to read more.

​2.  Hypothyroidism –

​Hypothyroidism refers to the condition of low levels of thyroid hormone in the body.

​The majority of cases are due to issues with the thyroid gland itself.  Rarely, it can be caused by issues in the brain (hypothalamic dysfunction).

​Since most thyroid hormone in the body is T4, if you are hypothyroid, you will have low levels of T4.

​That, however, ​does not give you enough information.  You need to investigate WHY you have hypothyroidism so that you can be appropriately treated.

​As we discussed earlier, the majority of hypothyroidism is caused by Hashimoto’s Thyroiditis.

​3.  Nutrient Deficiencies –

​There are multiple (at least 13) nutrients that are needed for proper thyroid hormone production and conversion.

A deficiency of even one of them can ​result in a significant reduction in thyroid ​levels which will cause symptoms of hypothyroidism.  It can also cause an increase in thyroid antibody levels if you have Hashimoto’s.

These nutrient deficiencies can include (click on the names for my preferred brands):

​So, should you just blindly supplement with all or most of these supplements if you have thyroid issues?

Of course not!

​You should always see your doctor and be tested for any nutrient deficiencies before supplementing, or at least look for common symptoms associated with particular deficiencies.  If you have a symptom or symptoms commonly seen with one of these nutrient deficiencies, then a trial of supplementation is reasonable to consider.

It is also always best to start with your diet.  Eat a diet high in nutrient-dense, organic foods which will contain a much higher nutrient content than the Standard American Diet.

​4.  Taking a T3 Only Medication –

​If you are taking a T3 only medication, it ​will often result in a drop in your T4 level.

T3 only medications include Cytomel and liothyroinine.  

Why?  It makes sense if you think about it.

​Like we learned earlier, T4 acts as the storage reservoir for T3 in the body.

If you are taking a T3 only medication, then your need for ​that reserve of T4 decreases because you have bypassed the conversion process.  This therefore results in less T4 production by the thyroid gland.

Taking a T3 only medication will typically cause the free T4 level to decrease, the TSH level to decrease, the reverse T3 level to decrease, and the total T3 and free T3 levels to increase.

This can also happen to a lesser extent if you are taking a natural dessicated thyroid (NDT) such as Armour Thyroid, NP Thyroid, or Nature-throid.  That is because these medications contain about 20% T3 and about 80% T4.

The drop in T4 level in this case is expected and what you want.  It is not a sign of inadequate thyroid levels like it is in the other situations.

​Symptoms of Low T4

​Having a low T4 level typically results in all of the classic symptoms of hypothyroidism.  

The list of symptoms can be quite exhaustive, but the most common include:

  • Fatigue
  • Weight Gain
  • checkHair Loss
  • checkConstipation
  • checkCold Intolerance
  • checkDepression
  • checkBrittle Nails
  • checkDry Skin
  • checkMenstrual Irregularities
  • Infertility
  • checkBrain Fog

​For a more extensive list, click here.

The vast majority of doctors have been taught to use the TSH as their sole means of evaluating thyroid function.

In many cases of hypothyroidism, the TSH will remain normal until it has been present for many years. This is true with Hashimoto’s as well.

The T4 and T3 levels will typically drop earlier in the process than will the TSH.

That is another reason why you should ALWAYS ask for a complete thyroid panel when your thyroid is being evaluated.

​How to Raise Your T4

​Fortunately, raising your T4 level is usually straight-forward.

Reversing what is causing your low T4 is the key to successful treatment.

You will either want to increase the thyroid hormone your body produces itself, or you will need to supplement ​what your body produces with a thyroid hormone medication.

​1.  Lifestyle Interventions –

​Improving your diet, beginning an exercise program, improving gut function, and reducing stress should always be the first steps taken when treating ANY condition.  The thyroid is no exception.

​2.  Correct Any Nutrient Deficiencies –

​Identifying and correcting any of the nutrient deficiencies we discussed earlier will result in an increase in your body’s natural thyroid production and T4 to T3 conversion.

​3.  Supplement with a T4 Thyroid Hormone – 

​Taking a T4 only medication such as levothyroxine, Synthroid, or Tyrosint will result in an increase in the T4 level in the body.  

Keep in mind that if you have T4 to T3 conversion issues because of a nutrient deficiency or inflammation in the body (insulin resistance, leptin resistance, an autoimmune condition, etc), raising your T4 level may still not result in adequate T3 levels reaching the cells.  Symptoms of hypothyroidism may still not improve.

​4.  ​Reduce Thyroid Antibody Levels –

​If you have Hashimoto’s, there are dietary, supplement, and medication therapies that can help reduce thyroid antibody levels.  This will improve thyroid function and will help to raise the T4 to an optimal level.

Click here to read more.

​5.  Take T3 Thyroid Hormone –

​In addition to or even in place of T4 thyroid hormone, T3 hormone medication can be taken.

That may cause the T4 level to drop, but that is not a bad thing in this case.

There is an art to using T3 medication, so it is important that you find a medical provider with experience in using it.

Click here to read more.


​A low T4 level is commonly seen in hypothyroidism.  It is often present before the TSH level becomes abnormal.

​A low T4 is associated with several symptoms that can dramatically alter your quality of life.

Treatment to increase T4 levels typically involves correcting nutritient deficiencies, reducing inflammation, and taking thyroid medication.

Now it’s your turn…

​Is your T4 level low?

Is your TSH level ​low, normal, or high?

Are you having symptoms of hypothyroidism?

What treatment plan are you using?

Leave any questions or comments below.​