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What Is T3?

One of the most powerful hormones in your body is called Triiodothyronine, also known as T3

With Yasmin Akhunji MD

Thyroid hormones

T3 specifically supports brain function, heart function, and digestion, and it plays a role in your metabolic rate and bone health. In short, it’s got a big job. Let’s take a closer look at how your endocrine system works and how T3 is made.

T3 Hormone Production

Your endocrine system is made up of many moving parts. When it comes to T3 production, the main players are your pituitary gland, hypothalamus and thyroid gland. These all work together to ensure proper body function.

The process starts in the hypothalamus, in your brain. Your hypothalamus releases a hormone called the thyrotropin-releasing hormone, which then relays a message to your pituitary gland located at the base of your skull.

At this point, the thyrotropin-releasing hormone tells your pituitary gland to create yet another hormone called thyroid stimulating hormone (this is referred to as TSH).

The TSH then travels through your bloodstream and binds to cells in your thyroid gland. Here, it tells you thyroid gland to make more or less of T3 and T4. Once the gland makes T3 or T4, it then communicates back to the pituitary gland, telling it to stop producing TSH.

If this all sounds pretty complicated, don’t worry. It’s a complex system that endocrinologists are very familiar with. If you’re concerned about your thyroid health, be sure get a referral from your PCP for an endocrinologist who will better understand the nuances of how it works.

T3 Thyroid Hormone: A Closer Look

If you have a thyroid condition or if you’re being tested for one, your health care provider may have spoken with you about T3, or you may have had your T3 levels tested through blood work.

T3 has two forms:

Bound T3:

This form of T3 is found abundantly within the body. It attaches to proteins which circulate the hormone around the body.

Free T3:
Unlike bound T3, free T3 moves around the body unattached to protein. It’s not found in abundance, but is the active form of T3.

According to Dr. Yasmin Akhunji, a board-certified endocrinologist at Paloma Health, the T4 hormone is basically inactive. "It’s actually a storage hormone that works to transport T3 throughout your body. T4 must be converted to T3 before your body can actively use it," says Dr. Akhunji.

About 20 percent of your body’s T3 is delivered into your bloodstream by your thyroid gland. The other 80 percent is made by your liver or kidneys in a process called deiodination. In this process, your body converts T4 into T3, as T3 is the biologically active form of the thyroid hormone T4. This is why patients with underactive thyroids take synthetic T4 as medication.

T3 vs.T4

Like T3, T4 is also both bound or free (known as free T4). The bound T4 is not able to be used since it’s bonded to a protein. Free T4, on the other hand, can enter the tissues that need it more easily.

Normal T3 Levels vs. Low T3

If you are experiencing symptoms of hypothyroidism or hyperthyroidism, your healthcare provider may run a T3 test, along with tests to measure TSH, T4, thyroglobulin and autoimmune antibodies. These are standard blood tests.

Depending on your symptoms or health history, an ultrasound or biopsy may also be performed. If you already have been diagnosed with a thyroid condition, your healthcare provider may also test your T3 to assess your thyroid function.

T3 Blood Test and Other T3 Tests

There are a few kinds of T3 tests. Your doctor may perform a test to measure both bound and free T3. This is called a total T3 test. Your doctor may also test your free T3 alone. Both tests should be able to help to put together a picture of your thyroid health, although there is no single test to determine thyroid disease.

What is a total T3 test?

A total T3 test is usually used to help determine if a patient has hyperthyroidism, which is a condition marked by too much thyroid hormone.

Symptoms of hyperthyroidism include:

  • Nervousness, restlessness, and anxiety
  • Hair loss
  • Fatigue
  • Weight loss
  • Sleeping issues
  • Bulging or staring eyes
  • Shaky hands
  • Feeling too hot

Understanding Your T3 Test Results

T3 level test results could also help determine hypothyroidism, which is a condition marked by low thyroid hormone.

Symptoms of hypothyroidism include:

  • Fatigue
  • Weight gain
  • Constipation
  • Brain fog
  • Muscle aches
  • Depressed mood

High total or free T3 levels could indicate a few health conditions, including:

  • Grave’s disease, an autoimmune disease that leads to the overproduction of thyroid hormones
  • Hyperthyroidism
  • Silent thyroiditis
  • Goiter, which is swelling of the thyroid gland
  • Thyroid cancer
  • Thyrotoxicosis, a condition marked by too much T3 in the body. This can stem from Grave’s disease, a tumor or inflammation in the thyroid.

Elevated T3 levels could also point to pregnancy, or the use of birth control pills. This is because estrogens in the body can increase T3 levels. If you are on birth control or are pregnant, it’s better to have your doctor look at your T4 and TSH. Liver disease can also increase your T3 levels.

Lastly, be aware that the use of the supplement biotin should be avoided in the days around thyroid bloodwork, as it can skew results.

Low T3 Levels

If your T3 is very low, it could also point to another health condition. Often, people who are very ill or hospitalized have low T3. Low T3 could also point to hypothyroidism. When people have too little thyroid hormone, they may have Hashimoto’s disease, an autoimmune disorder that causes hypothyroidism.

However, it’s worth noting that T3 testing alone is not enough for patients who suspect hypothyroidism. This is because T3 may appear normal in cases of hypothyroidism, while TSH and T4 are abnormal. 

"To get the best sense of your thyroid health, you’ll want to test for free T3, TSH and free T4," says Dr. Akhunji.

What are normal thyroid hormone levels?

Although there is no normal range agreed upon by all health care practitioners (some labs also have different ranges), the following ranges are generally considered typical for adults:

  • T4: 5.0 – 11.0 ug/dL
  • FT4: 0.9 - 1.7 ng/dL
  • T3: 100 - 200 ng/dL
  • FT3: 2.3 - 4.1 pg/mL
  • TSH: 0.40 - 4.50 mIU/mL

How to Heal Your Thyroid

If your test results show that your thyroid hormones are off, your doctor will generally prescribe medication to help you find a balance. Thyroid hormone replacement is common for hypothyroidism patients. Patients may be prescribed synthetic thyroxine (T4), which is also known as levothyroxine. With this medication, the T4 gets converted into T3 within the body. Anti-thyroid medications, such as methimazole and propylthiouracil, are typically prescribed to patients with hyperthyroidism.

There are also plenty of ways to augment a medication regimen and support a healthy thyroid.

Your diet is key when it comes to balancing healthy thyroid hormones. Limit processed foods, and fill your plate with lean proteins, greens, vegetables, fruits and minerals like iodine and selenium, which are essential to thyroid function. Reach for dark green veggies, brown rice, pinto beans, dates, Brazil nuts, and seafood.

Keep your stress levels low, as they can negatively impact your thyroid, especially if you have hypothyroidism. Although it can be challenging to reduce stress in today’s world, it’s important that you find the right method for you. Try using exercise, journaling, meditating or deep breathing to help diffuse stressful situations.

Daily movement is also vital, but be careful not to tax your system too hard. An underactive thyroid could lead to a slower heart rate, while an overactive thyroid could mean your metabolism is already revved up, including your heart. Try yoga, walking, light jogging and opting for the stairs over elevators or a longer walk to the car to ease into adding more movement into your routine.