What are T3 and T4?


The thyroid gland is essential to the optimum functioning of our bodies, as it regulates how quickly and efficiently our body cells work. As a result, it’s crucial that the thyroid gland is kept in good working order. But how exactly does it function?

Here, we’ll explore the thyroid gland and the two main hormones it creates: triiodothyronine, which is most commonly known as T3 and thyroxine, often referred to as T4.

What’s the thyroid gland? 

The thyroid is a major part of your body’s endocrine system, which is made up of glands that create and secrete hormones into our blood and to all the cells and tissues in our body.

Your thyroid gland creates hormones that control metabolism. Found in the base of your neck and shaped like a butterfly, this gland regulates critical bodily functions including: heart rate, breathing, muscle strength, body temperature, and cholesterol. It’s only around two inches in length and is comprised of two lobes that sit on either side of the windpipe.

The differences between T3 and T4

As we mentioned, the job of your thyroid gland is to send the hormones T3 and T4 into your bloodstream. But why and what exactly are these hormones?

The major difference between T3 and T4 is that the former is comprised of three iodine atoms and the latter made up of four. Although both are secreted into the blood by the thyroid gland, T4 is actually also converted into T3 within our body cells. However, it’s the T3 hormone that is biologically active in influencing the activity of our cells and tissue.

How do T3 and T4 hormones work? 

Having the right levels of T3 and T4 is crucial to general wellbeing. To ensure this, the hypothalamus and pituitary glands in our brain communicate with each other to keep our T3 and T4 levels in check. Our hypothalamus makes a hormone known as ‘TRH’ that indicates to the pituitary gland that it needs to tell the thyroid to create more or less T3 and T4. It does this by upping or lowering the secretion of a thyroid-stimulating hormone.

What happens if our T3 and T4 levels are wrong? 

The hormones T3 and T4 are vital for keeping our bodies ticking over healthily; regulating everything from how fast our heart is beating to how quickly our intestines are processing our last meal.

So, how are we affected if the amount of T3 and T4 in our bodies is incorrect? People with levels that are too high (a condition known as hyperthyroidism) will typically suffer with:

  • Irritability.
  • Weight loss.
  • High heart rate.
  • Anxiety.
  • Shaking.
  • Sweating.
  • Hair loss.

Alternatively, those whose levels are too low (hypothyroidism) will sometimes suffer with:

  • Slow heart rate.
  • Weight gain.
  • Fatigue.
  • Dry hair and skin.
  • Muscle pain.
  • Depression.
  • Trouble concentrating.

Evidently, maintaining optimum levels of T3 and T4 hormones is essential to overall good health and wellbeing. Fortunately, there are many ways to help with thyroid gland issues including adjusting our diets, quitting smoking and taking certain medications such as Cytomel tabs (also known as liothyronine). But remember to always consult a doctor before starting a new medication.