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  • Writer's pictureGavin Guard, Medical Director

What causes low thyroid?

Updated: Jan 23, 2022

In this article, you are going to learn more about your thyroid (the hard, shield-shaped, ductless gland placed in front of your throat. Think adam's-apple location) .

Specifically, you will have a greater understanding about what your thyroid does, reasons that it may not be working properly, and common symptoms that occur with a dysfunctional thyroid.

Let’s start with the first thing: understanding your thyroid’s function in the body.

You may already know some common symptoms of low thyroid (hypothyroid):

  • weight gain

  • fatigue

  • dry skin

  • cold feet and hands

  • cracked nails

  • constipation

  • fluid retention

  • high cholesterol/lipids

  • depression

Let’s keep these in mind as we uncover the role of thyroid hormone.

How the thyroid affects gut health

Thyroid hormone is a vital signal for your gastrointestinal tract (GI). It’s needed to stimulate your migrating motor complex which is the nervous system of your gut. Just a fancy way of saying thyroid helps create movement of food through your gut system. Interestingly, 15% of those who are hypothyroid have less than 3 bowel movements per WEEK! I don’t know about you, but a daily poop is kind of mandatory for me. Anything that deviates from that norm, I consider problematic.

Learn how probiotics can help your thyroid

Thyroid is also a key stimulator of hydrochloric (HCl) acid production in your stomach. HCl is produced by the hard working parietal cells of your stomach. When we think of metabolism, we must also consider mitochondria. With this in mind, it’s important to note that parietal cells have a TON of mitochondria in them that are “turned on” with the signaling of thyroid hormone.

Don’t have functioning mitochondria, have antibodies that tag them for destruction, or have low thyroid? If there’s a yes to any of these, you can say “goodbye” to proper digestion. Don’t have good digestion, then you most likely won’t be absorbing the key micronutrients from your food needed for thyroid hormone production and mitochondria function. You see where this loop is going?

How thyroid affects metabolism

Why is hypothyroid associated with weight gain? Thyroid hormone increases the amount of a protein in cells called uncoupling proteins. Thyroid collectively induces mitochondrial activity, “metabolism”, and makes your cell less efficient at making energy so you burn more Calories and lose energy as heat (instead of making ATP).

How the thyroid affects sex hormones

Let’s look at how thyroid affects testosterone and sex hormones. In a few animal studies (poor rats and goats), thyroid hormone administration increases the amount of steroid hormone production.

Furthermore, thyroid may help sex hormones receptor sensitivity increase its sensitivity. Why is this? Well, the rate-limiting step (if this doesn’t happen, the process won’t be completed) of sex hormone production is getting cholesterol into the mitochondria with the help of a protein called StAR (steroidogenic acute regulatory protein). The mitochondria then turns cholesterol (through many steps) into testosterone.

Your low thyroid levels could be one of the reasons you have issues with your sex hormones. Fix your thyroid before going straight to sex hormone therapy.

How thyroid affects body composition

Finally, let’s look at thyroid’s impact on muscle mass and body composition. It looks like thyroid influences muscle tissue in many ways. Thyroid hormone stimulates the proliferation and differentiation of skeletal muscle stem cells (baby muscle cells) into mature, functioning muscle cells. Also, thyroid induces the switch from slow-twitch to faster-twitch muscle cell types. It also increases insulin sensitivity which helps us to regulate blood sugar better.

What causes thyroid issues

Now let’s discuss how you can develop hypothyroidism (low thyroid).

Playing with fire!

Making thyroid hormone is no easy process. Many nutrients and minerals are necessary for the proper synthesis of thyroid hormone in the thyroid gland. A crucial enzyme involved in this process is called thyroid peroxidase (TPO). TPO is the enzyme that sticks iodine molecules on an amino acid to eventually make thyroid hormone (T3 and T4). This is one of the biggest and “dangerous” steps of making thyroid as TPO uses hydrogen peroxide (H2O2) to for this reaction to occur.

Remember how your mom used to pour H2O2 on a cut? You would brace yourself as you saw the liquid cause a “fizz” over the wound. That is because H2O2 is a very reactive molecule and causes oxidative damage in the body. That’s why we say that TPO is “playing with fire”. The enzyme is using H2O2 (a very reactive molecule) to complete an important step in the pathway of making thyroid hormone.

So how does our body deal with this? Well, we need many cofactors and nutrients to recycle H2O2 to produce thyroid hormone.

Specifically, the cell utilizes glutathione, zinc, manganese, copper, cysteine, glycine, and vitamin C to deal with this oxidative damage. If you don't have adequate supply of these nutrients, then you can start to see how the system breaks down.

How our nutrition affects thyroid

Our thyroid gland produces about 85 mcg of thyroid hormone per day. However, there is about 500 mcg of thyroid hormone stored in the thyroid gland in a person with normal thyroid levels.

What this tells us is that the majority of thyroid hormone levels are dictated at the level of the brain. A part of the brain called the hypothalamus tells the thyroid to release thyroid hormone to the rest of the body.

Interestingly, the hypothalamus is the same part of the brain regulates food intake. The hypothalamus is very sensitive to hormonal signals (e.g. leptin, ghrelin) that cues it to the level of energy stores in the body (body fat mostly).

When energy stores get low, the brain puts a halt on thyroid release, and thus you can develop hypothyroidism.

This makes sense as you recall that one of thyroid’s main jobs is to increase metabolism by making energy production less efficient. We wouldn’t want our body to run through energy stores if we were facing starvation, would we? Most of us don’t actually face starvation but our brain perceives that we might be when we chronically eat much less than our body’s energy demands.

This isn’t a reason to go stuff your face with a pizza so you can tell your friends, “it’s for my thyroid”. Rather, it’s a cue to work with someone you can trust to help you figure out how your nutrition could be impacting your thyroid levels.

How medication affects thyroid levels

Many prescription medications can exert a negative influence at all parts of the thyroid axis, from production to conversion.

The enzyme responsible for converting the inactive form of thyroid hormone (T4) to the active form (T3) is called deiodinase. This enzyme cuts off an iodine molecule from the protein backbone of the hormone, hence going from only 4 iodines (T4) to 3 iodines (T3). This process renders the hormone active and able to exert its duties to all cells in the body (thyroid hormone receptors are found everywhere in the body).

This enzyme can be inhibited by many medications such as steroids, amiodarone, and beta blockers. If your doctors runs a normal thyroid blood panel, then you may see normal levels of T4 and TSH (the hormone that tells the thyroid gland to release more thyroid). What they aren’t seeing is that while you have normal T4, your body is failing to properly convert it to the active form of T3. That’s reason to order a more comprehensive thyroid panel including other makers that give us a broader picture of the whole thyroid axis.

Bottom Line

I hope this article brought some clarity into the confusing world of hormones. The long-story short is that there are many causes for low thyroid and simply replacing thyroid hormone without asking "why" it's low in the first place is probably not the best answer.

Like what you are reading? Learn more about how to take control of your health by signing up for the "5 Minute Health Makeover" below where I coach you through 3 pivotal strategies for better health.

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