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Understanding Thyroid Hormones: What Is the Difference Between T3 and T4?

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Examining patients thyroid

The difference between thyroxine (T4) and triiodothyronine (T3) will aid you in understanding their roles in a healthy thyroid. 

While T3 and T4 are hormones produced by the thyroid gland, they differ in terms of their form and how body tissues use them. Many organs don’t use inactive T4 and must convert it into active T3. It has to remain available in the bloodstream to maintain endocrine balance. 

Keep reading to discover the difference between T3 and T4. Learn how to maintain healthy thyroid hormone levels and other frequently asked questions.  

Difference Between T3 and T4 Thyroid Hormones 

As thyroid hormones, T3 and T4 play crucial roles in metabolism and digestive functions. However, they have several differences warranting independent monitoring when it comes to secretion quantity to detect hypothyroidism or hyperthyroidism. 

For one, T4 contains four iodine atoms, and T3 contains three. Hence, the numbers in their respective acronyms. T4 is also the inactive form, while T3 is the active counterpart which means tissues need to convert T4 into T3 by removing an iodide through selenium-containing enzymes. This process is called deiodination. 

Moreover, T4 is only produced by the thyroid gland and cannot be formed elsewhere. On the other hand, T3 is created in the thyroid gland and some other organs. 

Did You Know? Aside from T3 and T4, it’s important to assess your thyroid-stimulating hormone (TSH) or thyrotropin. TSH stimulates the secretion of thyroid hormones. Therefore, abnormal T3 and T4 can be traced back to TSH production problems in the brain’s pituitary gland. 

What is the function of T3 and T4?

T3 and T4 regulate the body’s metabolic rate, influencing how much and how fast you burn calories and the breakdown of proteins, carbohydrates, fats, and vitamins. As a result, they also contribute to controlling heart rate, body temperature, immunity, and cognitive functions. Individually, both hormones also portray separate roles.

  • T3 Functions: fetal development of bones and connective tissues, resting respiratory rate regulation, stimulation of alertness, growth hormone production, ovarian cycle, and protein synthesis
  • T4 Functions: heart and muscle function, weight regulation, maintaining bone health, and aiding in brain development

Excessive or low production of T3 and T4 tips off other organ functions, especially as they are crucial components in the most basic physiology. Hence, it’s imperative to keep them within the normal range. 

How to Maintain Healthy T3 and T4 Levels 

Smiling mature loving couple family standing at the kitchen

Keeping your T3 and T4 at healthy levels is imperative for your good health and wellness. Although you may experience imbalances due to clinical reasons, there are actions you can do within your means to prevent critical highs or lows when it comes to thyroid hormone production. 

Also, on top of medical treatments, talk to your doctor about these supplementary ways to naturally correct the T3 and T4 imbalance. 

Eat Thyroid-Friendly Foods

Thyroid health often relies on specific nutrients to maintain the organ’s function. By supplying these nutrients adequately, you keep thyroid production within the healthy scale. These nutrients include the following:

  1. Iodine

Iodine is an essential component in synthesizing T3 and T4. In fact, both thyroid hormones are made of iodine combined with tyrosine, an amino acid. Therefore, how much iodine you absorb from several foods and supplements determines the amount of thyroid hormones produced. 

Foods Rich in Iodine: shellfish, seaweed, “iodized’ salts, fish, dairy, poultry, organ meats, and lima beans

  1. Selenium

This trace mineral protects thyroid function. In addition, selenium provides antioxidants – being part of selenoproteins – which strengthens the thyroid gland’s defense against cancer and related disorders. 

Foods Rich in Selenium: poultry (chicken and turkey), red meat (beef and pork), fish, shellfish, eggs, nuts, and beans

  1. Iron

Iron is another nutrient that keeps the thyroid gland functioning well. It mainly influences the breakdown of T4 and T3. According to a 2017 study, iron deficiency anemia impairs the metabolism of thyroid hormones. 

Foods Rich in Iron: organ meats, red meat, dark chocolate, shellfish, beans, spinach, broccoli, and sweet potato

  1. Zinc

Your thyroid gland needs zinc to synthesize T3 and T4 as it regulates the production of substances that influences their metabolism, such as enzymes, TSH, and thyrotropin-releasing hormone (TRH). 

Foods Rich in Zinc: oysters (and other shellfish), nuts, beans, red meat, poultry, whole grains, and fortified breakfast cereals

  1. Manganese 

Manganese contributes to the production and release of T4. Hence, if your body lack manganese, your thyroid gland may not function well. This mineral also helps form Manganese  Superoxide Dismutase, an essential antioxidant that defends the thyroid gland from free radicals. 

Foods Rich in Manganese: shellfish, legumes, nuts, whole grains, rice, coffee, and leafy vegetables

  1. Magnesium 

The amount of magnesium in your body also influences the secretion of T3 and T4. A 2018 study shows that extremely low magnesium levels increase your risk of developing thyroid problems, including hypothyroidism. 

Food Rich in Magnesium: dark green leafy vegetables, whole grains, seeds, nuts, rice, banana, broccoli, peanut butter, and breakfast cereals

Plan your diet in such a way that includes the list of food mentioned above. Doing so allows you to supply the right nutrients adequately, which helps your thyroid gland to secrete T3 and T4 in healthy amounts. 

Become More Physically Active

First lessons bicycle riding. handsome grandather teach his granddaughter to ride a bike. practicing near home.

If you’re looking for a specific reason to exercise regularly, look no further than keeping your thyroid healthy, especially against hypothyroidism. 

Multiple studies support that aerobic exercises and moderate workouts increase T3 and T4 as well as improve the production of TSH. This means if you have low thyroid hormones, consider getting into light physical activities you can do at home. 

Which type and workout intensity you should go for depends on your current condition with your thyroid health. For an on-point recommendation, consult with your healthcare provider first. 

Manage Stress Well

So many events inside your body occur when you’re stressed. One is the alteration of thyroid hormone secretion due to the increased release of cortisol (stress hormone) and adrenaline (flight-or-fight hormone).

A 2020 study shows that high cortisol disrupts the production of TSH and T4, prompting hypothyroidism. This was particularly determined among patients with cortisol-producing adenoma (CPA). The condition was found to be reversible after the surgical removal of the tumor.

Nonetheless, it showed that abnormal levels of cortisol, which can be produced through consistent stress, bring down thyroid hormones. 

With this information, it’s best to employ several stress management techniques to help you combat the cortisol imbalance, such as meditation, taking deep breaths, getting a hobby, practicing self-care, eating healthy, and more. 

Did You Know? Unhealthy ways of coping with stress, like sleeping more, binge-watching shows, and self-isolation, do more damage than good to your thyroid and your body as a whole. Instead, choose the most effective ways to deal with stress that positively impacts your physical and mental health. 

Check Your Thyroid Health

Detecting problems in your T3 and T4 production at their onset determines how long your thyroid can function normally again. Hence, as hormone imbalance symptoms show up, take the necessary blood test so your doctor can diagnose accurately. 

If you want more insights on your thyroid hormones, take the thyroid panel with a TSH blood test. You can also explore other labwork specific to your needs when visiting our thyroid function tests category.  

Want to learn more about how to protect your thyroid health on your own? Check out 6 Ways to Improve Your Thyroid Function Naturally

Frequently Asked Questions 

Which is more important, T4 or T3?

Both thyroid hormones are essential to ensure your vital organs function well since they regulate energy conversion. In terms of monitoring thyroid health, assessing the free T4 in the bloodstream is more important than T3. T4 is solely produced in the thyroid gland, while a significant concentration of T3 gets converted from T4 by other tissues.

Why is my body not converting T4 to T3?

Your body may fail to convert T4 to T3 if you have health problems in your liver and gut. For example, if you have inadequate gut bacteria like E.coli in your intestinal tract, the amount of T3 generated from T4 can be significantly lower. Not to mention impaired microbial population in the gut affects the absorption of nutrients like iodine, iron, and selenium which are essential in the production of thyroid hormone. 

If your T4 is high but your T3 is low, it may not necessarily be due to hypothyroidism. Still, it’s more beneficial to be completely sure – don’t hesitate to get the optimal thyroid profile blood test

How do I know if I need T3?

You might have to improve your T3 production if you get diagnosed with hypothyroidism, hyperthyroidism, or other thyroid disorders. 

Although each clinical condition associated with thyroid functions have distinct symptoms, your body will generally hint at thyroid problems if you exhibit the following: fatigue, weight gain, irregular heart rate, and sensitivity to temperature changes. Consult your doctor as soon as you spot these symptoms to have your thyroid health screened

What happens if only T4 is high?

If your blood test shows high T4, it could indicate hyperthyroidism linked to Grave’s disease, toxic goiter or enlarged thyroid gland, or thyroiditis (inflamed thyroid gland). But for your healthcare provider to form an accurate diagnosis, your T3, TSH, and thyroid peroxidase (TPO) has to be evaluated. 

The Bottom Line 

The difference between T3 and T4 hormones allows physicians to narrow down the possible cause of a certain thyroid gland disorder. While both are thyroid hormones of equal importance, their discrepancies reveal specific imbalances and impairment. If you experience symptoms pointing to thyroid function problems, consult your doctor immediately and get the proper thyroid function test

Medically Approved By Dr. Edward Salko, MD

Dr. Edward Salko is the board-certified physician who reviews lab tests provided by PERSONALABS™. He earned his Bachelor of Science in chemistry and pre-med from the University of Florida in Gainesville and his Doctor of Osteopathy Medicine in 1980 from Kansas City University School of Medicine.

Dr. Salko’s career has specialized in family and emergency medicine. His passion is to provide clients with the tools they need in the most convenient way possible to allow them to take charge of their own healthcare. He has held a variety of positions in Kansas, Florida and Washington. Currently, in addition to his duties as Medical Director for Personalabs, he is a practicing emergency physician in Kennewick, Washington.

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