Overview
The thyroid gland produces two different types of hormones, the iodothyronines and Calcitonin. While calcitonin plays a huge role in our bodies, it will be the iodothyronines that we will focus on as they are the major players in thyroid disorders. So, what are the iodothyronines and what functions do they serve in the body?
There are two different kinds of iodothyronines (which will be referred to as “thyroid hormones” from here on out) and they are thyroxine (T4) and triiodothyronine (T3). These two hormones are absolutely essential and necessary for body development, growth and energy metabolism among other things. Thyroxine (T4) is what is known as a “prohormone” meaning that on it’s own, it has little to no effect and must be converted in the body to the biologically active form which is triiodothyronine (T3). There are many steps that go into the process of producing these thyroid hormones in the thyroid gland. It can certainly get confusing and complicated but most important parts to understand about the process are:
· It is essential to have the necessary amounts of iodide available in the body (iodide is a single ion whereas iodine is a compound). Not having the necessary amount of iodide in the body can lead to a lack of hormone production and an enlarged thyroid gland, also known as a goiter.
· Having the appropriate amount of another hormone known as thyroid stimulation hormone (TSH) is also essential. TSH is a hormone that signals the thyroid to make thyroid hormone. TSH comes from the pituitary gland.
- The ability of your body to convert the T4 hormone into the T3 hormone.
The last point in an interesting one. As mentioned in the opening paragraph, T4 is a prohormone and it not very active in the body by itself. It needs to be converted to the active form, T3. Our bodies actually produce MUCH more T4 than it does T3! In fact, about 60-80% of the thyroid hormones that are body produces is T4 and must be converted to T3. While our thyroid does produce some T3 on its own, the vast majority of the T3 that is in our body at any given time has been converted from T4. So it’s pretty clear that the conversion of T4 to T3 is hugely important to the proper functioning of our bodies. Unfortunately, some people possess a decreased ability to perform this conversion and because of this, they need different medications than someone who is able to properly convert the hormone.
So what are the functions of the thyroid hormones?
- They play a huge role in brain and total body development.
- They regulate energy expenditure in the body and also regulate how your body takes in and consumes oxygen.
- They influence many different aspects of heart function includes how hard and how fast it beats.
- They greatly impact of bodies metabolic processes including how we metabolize our food and how our body deals with fat and cholesterol.
Causes
Disorders of the thyroid can result in either too much or too little production of the thyroid hormones. When a medical practitioner wants to test how your thyroid is working, they typically will order what is known as a thyroid function test (TFT). Two of the most common tests that are performed measure two things in your body, TSH (thyroid stimulation hormone) and the amount of T4 in your body. There are additional tests as well, but these two are by far the most common. While we won’t spend much time discussing TSH, it is important to know that TSH does not come from the thyroid itself, but from the pituitary gland. TSH stimulates your thyroid to produce more thyroid hormone.
The most common disorder of the thyroid is hypothyroidism (low thyroid hormone). Hypothyroidism is actually divided into three separate categories, based on what the cause of hypothyroidism is.
- Primary hypothyroidism – This occurs in people that who cannot, for a variety of reasons, produce enough thyroid hormone themselves. The reasons include an autoimmune disorder known as Hashimoto’s disease and insufficient iodine intake. In developed countries of the world, insufficient intake of iodine is extremely rare. Iodine is most commonly added to table salt (ever wonder why salt is commonly sold as iodized salt?) And we therefore generally intake sufficient amounts.
- Secondary hypothyroidism – This occurs in people who have some sort of disease that impairs TSH (thyroid stimulating hormone). When TSH is impaired, your thyroid isn’t getting the message to make enough thyroid hormone.
- Tertiary hypothyroidism – In this type, your hypothalmus doesn’t produce enough of a hormone that stimulates your pituitary gland to release TSH.
As we can see, there are a lot of areas where things can go wrong. Aside from primary hypothyroidism, many times the problem doesn’t lie with the thyroid itself, but with other glands and hormones that are in the pathway of producing sufficient thyroid hormones.
Typically, the symptoms of hypothyroidism start mild and tend to progress the longer it goes untreated. The most common effects of hypothyroidism are:
- Fatigue
- Feeling cold or chilled
- Weight gain
- Constipation
- Brittle and easy to break nails
- Loss of hair
- Dry and itchy skin
- Joint pain
- Voice changes
- Poor appetite
- Slowing of normal heart rate
As we can see, there are MANY possible physical manifestations of having low thyroid hormone. People typically describe the symptoms on a whole as just feeling “blah”.
If hypothyroidism is not treated and continues to get worse, there are some serious problems that could occur including:
- Coma
- Heart attack
- Enlarged thyroid (known as a goiter)
Medications
There are many different medications that can be used to replace the low thyroid hormone in the body. The three most common are listed below:
- Levothyroxine (Multiple brand names including Synthroid, Levothroid and Unithroid)
- Liothyronine (Brand name Cytomel)
- Dess
icated thyroid (Multiple brand names including Armor Thyroid and Nature-Throid)
We will discuss each of these medications in detail.
Levothyroxine
Levothyroxine is by far the most commonly prescribed medication for thyroid replacement therapy. Levothyroxine is a synthetic preparation of the T4 thyroid hormone, and as mentioned in previous sections, needs to be converted to the active T3 hormone in the body. Why is the most commonly prescribed thyroid replacement medication T4 as opposed to the already active T3? It’s a fair question, especially since many people cannot or have an impaired ability to make T3 from T4. The answer to the question is because it has consistent potency (since it is made synthetically, variability is strength is extremely low from tablet to tablet) with every dose and because it has predictable absorption / long duration of action. It typically is dosed only once daily. Levothyroxine is also the least expensive medication for thyroid replacement.
It is extremely important to take this medication (and all thyroid medications) at the same time every day. The most common recommendation is to take your dose first thing in the morning when you wake up with a full glass of water and you should not eat or take any other medications for at least 30 minutes. This recommendation is here because the dosages of thyroid hormone are small! The typical dose for people is 112 micrograms. That is 1/1000 of 112 milligrams and 1/1000000 of 112 grams! We are talking about an extremely small dosage here. A small change in absorption can greatly impact the effects your medication will have on you. Typically, after you start your thyroid medication, you will have a follow up appointment with your doctor in 6-8 weeks to see if you need a dosage change.
Liothyronine
Also known as Cytomel, liothyronine is synthetic T3 hormone. The advantage of liothyronine is that it does not need to be converted like levothyroxine does to become active. This is certainly a positive attribute for patients that have an impaired ability to convert T4 to T3. Liothyronine also has a slightly faster onset of action than levothyroxine does. With all of these positive aspects, one might wonder why liothyronine isn’t the most popular thyroid replacement medication. Well, firstly, liothyronine is more expensive than levothyroxine. Secondly, partly due to it’s faster onset of action, it has historically has been associated with having a risk of cardiotoxicity. It is because of it’s faster onset of action that it may increase the T3 in your body too high for a short period of time which could cause issues. Lastly, while overwhelmingly it is dosed once daily, it does in some people need to dosed twice daily because it does not have the long duration of action that levothyroxine does. In terms of taking liothyronine, it should be taken the same way as levothyroxine, by itself first thing in the morning.
Dessicated Thyroid
Dessicated thyroid goes by many names, but it most commonly sold as Armor Thyroid. Dessicated thyroid is actually animal thyroid gland (most commonly pig) that has been cleaned, powdered, dried and then formed into a variety of dosage forms. There are two main features of dessicated thyroid that differentiate itself from the other medications. Firstly, and maybe most importantly, it is a natural medication and contains the natural thyroid hormones. It is not synthetic as the other medications are. Secondly, dessicated thyroid contains BOTH T4 and T3. There has been and probably always will be controversy over the use of dessicated thyroid. Some positive attributes are the fact that it is natural, it contains both T4 and T3 (although studies are not conclusive if this has any benefit), and a good supply of anecdotal evidence. The main negative of this form of thyroid is the fact that there may be some variability in terms of dose from tablet to tablet. It is much harder to get precise dosages every time because of the manufacturing process vs. the synthetic versions of thyroid. Also, dessicated thyroid can be hard to dose by practitioners and is very commonly increased in dosage until symptoms get better in patients. Many practitioners like to depend on hard lab values as opposed to chasing symptoms. Dessicated thyroid typically is not recommended as first line therapy by many medical organizations.
