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Should Those With Subclinical Hypothyroidism Take Thyroid Hormone Replacement?

Levothyroxine is one of the most commonly prescribed medications in the United States.  In fact, a few years ago synthetic thyroid hormone was THE MOST commonly prescribed medication, while in 2017 it was the second most popular prescription, followed by hydrocodone-acetaminophen (1) [1].  While millions of people take synthetic thyroid hormone, more and more people are taking desiccated thyroid hormone (i.e. Armour, Nature-Throid, WP Thyroid).  Although many people need to take thyroid hormone replacement, there are also people who shouldn’t be taking it.  If you’re unsure whether or not you should be taking thyroid hormone replacement, hopefully you’ll have a better idea after reading this blog post.

Having healthy levels of thyroid hormone is essential.  But why is thyroid hormone so important?  Thyroid hormone not only plays an important role in metabolism, but it also regulates many bodily functions.  As I discussed in an article entitled “Why Is Thyroid Hormone So Important To Our Health [2]“, thyroid hormone has some of the following roles:

Overt Hypothyroidism vs. Subclinical Hypothyroidism

Overt hypothyroidism is when one or both thyroid hormone levels are below the lab reference range.  On the other hand, subclinical hypothyroidism is when the TSH is elevated, but the thyroid hormone levels are within the lab reference range.  The name “subclinical” can be misleading, as many people who are classified as having subclinical hypothyroidism are symptomatic, while others with subclinical hypothyroidism don’t experience any hypothyroid symptoms.

Subclinical hypothyroidism is considered to be mild when the TSH levels are between 4.0 and 10.0 mIU/l.  On the other hand, when the TSH is greater than 10.0 mIU/l it is considered to be severe.  This has limitations, as the TSH can fluctuate, and different labs will have different reference ranges.  It’s also important to understand that the severity of symptoms doesn’t always correlate with how high the TSH is.  For example, I’ve worked with patients who had a TSH greater than 10 mIU/l and didn’t feel too bad, but I’ve also consulted with patients whose TSH were within the lab reference range but felt lousy.

This brings up another discussion on the “lab” reference range vs. the “optimal” reference range.  For example, according to many functional medicine practitioners the “optimal” reference range for the TSH would be between 1 and 3 mIU/l.  But some labs don’t consider the TSH to be elevated unless if it is above 5.0 mIU/l.  The same concept applies with the thyroid hormone levels, as many people have thyroid hormone levels that are within the lab reference range, but are suboptimal.

What Causes Subclinical Hypothyroidism?

The most common cause of subclinical hypothyroidism is Hashimoto’s thyroiditis.  As discussed in other articles and blog posts, this is characterized by an elevated TSH and elevated TPO and/or thyroglobulin autoantibodies.  Other potential causes of subclinical hypothyroidism include a genetic polymorphism of the TSH receptor, transient TSH elevation during recovery from severe illness, untreated primary adrenal insufficiency, taking various drugs (i.e. lithium, amiodarone), and the presence of heterophile antibodies (2) [3] (3) [4].

What Are The Risks of Untreated Hypothyroidism?

If someone needs to take thyroid hormone replacement but chooses not to take it, what are the potential risks?  Well, one risk is that they might have to deal with symptoms that they wouldn’t otherwise experience if they were to take thyroid hormone.  I’ve worked with patients over the years who had moderate to severe hypothyroid symptoms but refused to take thyroid hormone replacement for various reasons.  But besides helping to decrease hypothyroid symptoms, remember that thyroid hormone has many important functions, as earlier I mentioned how it plays an important role in brain development, bone health, reproductive health, regulating gene expression, the metabolism of proteins, carbohydrates, and fats, and peripheral nerve regeneration.

In addition, there is some evidence that untreated subclinical hypothyroidism can increase the risk of developing cardiovascular disease.  In an article I wrote entitled “LDL Particles, Lipoprotein A, and Thyroid Health [5]”, I discussed how having high LDL particles and lipoprotein a, which is also known as Lp(a), can increase one’s cardiovascular risk.  And having low thyroid hormone levels can lead to increases in LDL particles and Lp(a).  I also came across a study which showed that high blood pressure was more common in those with subclinical hypothyroidism, although a few studies showed that there wasn’t a reduction of blood pressure upon taking thyroid hormone replacement (4) [6] (5) [7].

If you are pregnant and have subclinical hypothyroidism then there is an even greater risk of not taking thyroid hormone.  Some studies have shown that pregnant women with mild subclinical hypothyroidism have an increased risk of gestational hypertension and pre-eclampsia (2) [3].

What Are The Risks of Taking Thyroid Hormone Unnecessarily?

Perhaps the greatest risk of taking thyroid hormone replacement if you don’t need it is becoming hyperthyroid.  This can also occur if you need thyroid hormone replacement but take too high of a dosage.  For example, if someone has a mild case of subclinical hypothyroidism and they start with a dosage of 150mcg of levothyroxine, this very well might be too high.  But even if they had a severe case of subclinical hypothyroidism it probably would be wise to start with a lower dosage and gradually increase it.

Why Do Some People Who Need Thyroid Hormone Refuse To Take It?

There are a few reasons why people refuse to take thyroid hormone replacement, even if their blood tests indicate that they can benefit from it.  First of all, some people simply don’t think they need to take any type of exogenous hormone replacement.  While this is debatable if someone has subclinical hypothyroidism, if someone has overt hypothyroidism then there is a greater concern with not taking thyroid hormone.  Of course either way one needs to address the cause of the problem, and if someone has primary adrenal insufficiency that is causing overt hypothyroidism they need to address this first.  On the other hand, if someone has overt hypothyroidism that is caused by Hashimoto’s, although you still want to address the cause of the problem and restore the health of your immune system, while doing this it might be a good idea to take thyroid hormone replacement.

Another reason why some people don’t take thyroid hormone replacement is because they consider it to be a drug.  While it’s true that levothyroxine, as well as desiccated thyroid hormone, require a prescription, you shouldn’t put them in the same category as prescription drugs such as antibiotics, statins, acid blockers, etc.  The reason for this is because while people don’t have a deficiency of a statin or an acid blocker, they of course can have a deficiency of thyroid hormone.  I’m not trying to talk anyone into taking thyroid hormone, but if you truly need it but are avoiding it because you don’t want to take any “drugs”, I wouldn’t classify thyroid hormone as being a “drug”.

That being said, some forms of thyroid hormone replacement are superior to others.  For example, while a lot of people take Synthroid, this probably is the lowest quality form of thyroid hormone replacement available due to the fillers and artificial ingredients.  If you need to take synthetic T4 then consider a more hypoallergenic form such as Tirosint [8], or perhaps a more natural form such as Nature-Throid or WP Thyroid.

Another concern people have is that they will become dependent on thyroid hormone replacement.  In other words, once they start taking it they won’t be able to wean off of it.  The truth is that a “hormone dependency” can happen when taking any type of hormone, but I’ll also add that I’ve had many patients who were taking thyroid hormone replacement for many years prior to working with me who were able to wean off.  While it’s true that some people do need to remain on thyroid hormone replacement permanently, this isn’t the case with everyone.  And even if this were the case, you need to weigh the risks and benefits.

When Should You Take Thyroid Hormone Replacement?

Just in case you’re still unsure whether or not you should take thyroid hormone replacement, I’ll list a few situations when you will want to consider taking it.

1. If you have overt hypothyroidism.  If your thyroid hormone levels are below the lab reference range then you should strongly consider taking thyroid hormone replacement.

2. If you have a severe case of subclinical hypothyroidism.  Earlier I mentioned how the research considers a TSH greater than 10 mIU/ as being severe.  However, if someone in this situation has both thyroid hormone levels within the optimal reference range, then it is questionable if they should take thyroid hormone replacement.

3. If you have a mild case of subclinical hypothyroidism during pregnancy.  Of course the reasoning behind this is to decrease the risk of complications during pregnancy, as well as to reduce the risk of impaired cognitive development of the fetus.

4. If you have a mild case of subclinical hypothyroidism but experience severe hypothyroid symptoms.  This also is debatable, but I’ve had some patients who had a mildly elevated TSH and felt much better when taking thyroid hormone.

I’m not suggesting that there aren’t other scenarios when you would want to consider taking thyroid hormone replacement, but these are some of the situations when you should strongly consider taking it.

In summary, millions of people take thyroid hormone replacement.  And while there is a good argument that most people with overt hypothyroidism should take thyroid hormone, it’s more controversial when discussing whether people with subclinical hypothyroidism should take it.  Just as is the case with anything else, one needs to look at both the risks and benefits.  Some scenarios that might warrant someone with subclinical hypothyroidism taking thyroid hormone replacement are if their TSH is very high, if they are pregnant, and/or if they are very symptomatic.