The thyroid is a butterfly shaped gland that is located in the front of your neck, right below your Adam’s apple (or thyroid cartilage). The thyroid wraps around the trachea.
Every cell in your body has a receptor for thyroid hormone. This means every cell in your body needs thyroid hormone to function, but it needs exactly the right amount and type of thyroid hormone to function optimally.
In order to understand how the thyroid produces enough hormones we need to understand the role of the hypothalamus and pituitary.
The hypothalamus and pituitary reside in your brain and together regulate all hormones in your body. The hypothalamus is the master gland. It helps to link together the nervous and endocrine systems, regulate hunger, thirst and sleep, and control body temperature, just to name a few important jobs it has. But, it can’t do all of its jobs without help from the pituitary. The pituitary is a small size gland located at the base of the brain just under the hypothalamus. It takes lots of orders from the hypothalamus and in response releases various hormones in order to regulate homeostasis within the body.
The hypothalamus is constantly monitoring the levels of thyroid hormone in your blood. If levels seem low your hypothalamus will release thyrotropin-releasing hormone or TRH. TRH tells your pituitary to release thyroid-stimulating hormone, or TSH. TSH is sent directly to your thyroid. So as you can see proper thyroid function depends not only on the thyroid but also on the hypothalamus and pituitary.
Once your thyroid receives the TSH it takes iodine (a mineral) and tyrosine (an amino acid) from your bloodstream in order to produce thyroid hormones, which it then releases back into the bloodstream.
The tyrosine is converted into thyroglobulin (Tg) and then attaches to one, two, three or four iodine atoms, creating four different types of thyroid hormones - T1, T2, T3 or T4. You may not have heard of T1 or T2 before and that’s because the thyroid only creates a small amount of them and we don’t know much about either.
T4 is the primary hormone produced by your thyroid – some sources say it makes up 80% of your thyroid’s output – some say up to 93%, either way we know it’s a large portion of the total output. T4 is the storage form of thyroid hormone. It circulates through your bloodstream and is stored in your tissues, but does not enter your cells (in other words it does not affect your energy, metabolism or symptoms). But don’t be fooled into thinking it isn’t important just because it’s the inactive form.
Since the thyroid only releases about 7-20% of T3 the rest of it must be converted from T4. Since T4 is constantly in your tissues and bloodstream the body can pull T4 from either location and convert it into T3 whenever it needs more.
How does your body convert T4 into T3?
The process is triggered locally – so if you are pushing through a really tough workout and you’re trying to maintain a 40s/m pace on the rower the cells in your legs may need more thyroid hormone. When your stomach is working to break down and digest your dinner, your stomach cells will need extra thyroid hormone. This is constantly happening throughout the day. Different parts of your body will need more thyroid hormone based on the challenges they are facing.
The actual conversion of T4 to T3 happens in the gut, liver, skeletal muscle, brain and thyroid. The enzyme deiodinase is needed. And deiodinase needs selenium, zinc, and iron to properly do its job. Deiodinase removes one of the OUTSIDE iodine atoms, turning T4 into free T3. The free T3 is then ready and able to enter your cells.
So we now know not only is the thyroid important in this process but also the hypothalamus, pituitary, brain, liver, gut, skeletal muscle, AND a proper diet. Pretty intricate system right?
So how does T3 enter your cells?
T3 needs cortisol in order to enter your cells. Cortisol is produced by the adrenals. If cortisol levels are low (a sign of possible adrenal dysfunction) T3 will have trouble moving from your tissues to your cells. If you don’t get enough T3 into your cells you’ll start to have hypothyroid symptoms. The health of your cell walls is important as well. The stronger and healthier your cell walls are the better they can take in nutrients and hormones and keep toxins out. Cell walls are made of fat so it is essential to get healthy fats in your diet (healthy fats – coconut oil, avocados, olive oil, animal fat. Avoid unhealthy fats - processed oils like canola oil, hydrogenated fats, and trans fats like margarine).
Once in your cells T3 regulates your metabolism. The mitochondria inside your cells take in glucose and oxygen (from your blood) in order to make energy. Your thyroid needs to send in the right amount of hormone to each and every cell in order for this process to work optimally. And you want it to be working optimally because all metabolic processes are being controlled: heart rate, energy levels, brain function, weight regulation plus more. So if you have low energy, have trouble focusing or remembering things, difficulty losing weight or gaining it, it could be a sign something isn’t right with your thyroid.
I’ve covered T4 and T3, but we’ve got to cover reverse T3 (rT3) as well. Reverse T3, like T3 is also converted from T4. When T4 is converted into T3 one of the outside iodine atoms is removed. When T4 converts to rT3 one of the inside atoms is removed. Reverse T3 is another inactive form of thyroid hormone, like T4. Reverse T3 also attaches to the receptors inside your cells, where free T3 would normally go, leaving less room for T3. Reverse T3 has the opposite job of T3, it slows down your metabolism. The production of Reverse T3 will increase when you are more stressed, over exercise, or are on an extremely low calorie diet (another reason NOT to starve yourself in order to try to lose weight).
So to review:
TSH-Thyroid stimulating hormone, released by the pituitary and sent to the thyroid
T4- the inactive form of thyroid hormone, produced by the thyroid
T3- the active form of thyroid hormone, produced by the thyroid and converted from T4
Reverse T3- another form of inactive thyroid hormone, converted from T4 that slows the metabolism
The body is an intricate system, everything is linked and nothing works alone. As you hopefully realized from reading this, thyroid health is not just about the thyroid. It’s also about the liver, muscles, gut, hypothalamus, pituitary, cells and adrenals and eating a well balanced diet.