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What is Subclinical Hypothyroidism?

Written by Dr. Michael Ruscio, DC on August 26, 2024

Written by Dr. Michael Ruscio, DC on August 26, 2024 — Reviewed by Kellie Blake

How to Address Mildly Elevated TSH Levels

• Overview|
• The Root Cause|
• How to Treat|
• Diet and Lifestyle|
• Subclinical Hypothyroidism and Gut Health|
• Whether You Need Levothyroxine Therapy|

Ever heard of subclinical hypothyroidism? It sounds complicated, but this thyroid disorder is actually quite common, if a little misunderstood. Subclinical hypothyroidism is a 100% real diagnosis, defined as having mildly high TSH (thyroid-stimulating hormone) but normal T4 (thyroxine, an inactive thyroid hormone).

Many well-meaning functional medicine practitioners will jump straight to T4 or T3 (triiodothyronine, active thyroid hormone) replacement therapy to treat subclinical hypothyroidism. However, in most cases of mildly elevated TSH levels, the patient doesn’t actually need thyroid hormone replacement 1.

At the Ruscio Institute for Functional Health, we see subclinical hypothyroidism a lot. Eight times out of 10, our approach resolves mild thyroid hormone abnormalities before we even look at prescribing levothyroxine (T4 replacement therapy). Our guiding tenet is to make sure we don’t treat subclinical thyroid disease with long-term hormone replacement therapy if the signs and symptoms of overt hypothyroidism aren’t really there.

But before I get into our clinic’s treatment of subclinical hypothyroidism, let’s dive deeper into this thyroid disorder to understand its potential causes and some nuances of diagnosis and treatment.

Subclinical Hypothyroidism: An Overview

The incidence of subclinical hypothyroidism ranges from about 3% to 15% of the population 2. As I mentioned earlier, a subclinical hypothyroidism diagnosis is appropriate when thyroid-stimulating hormone (TSH) levels are mildly high (4.5–10 mIU/L) while free T4 (aka free thyroxine) levels are within normal reference range 3. 

No thyroid peroxidase (TPO) antibodies should be present unless you have a combination of Hashimoto’s thyroiditis and subclinical hypothyroidism. In contrast, overt hypothyroidism with or without Hashimoto’s comes with a serum TSH (aka thyrotropin) level over 10 mIU/L and low free T4 (below 0.8 mIU/L).

With or without Hashimoto’s thyroiditis, subclinical hypothyroidism doesn’t typically manifest symptoms, but it can present with symptoms of overt hypothyroidism, such as 4:

• Dry skin
• Hair loss
• Constipation 
• Loss of appetite
• Weight gain
• Brain fog
• Anxiety
• Fatigue
• Irregular menstrual cycles

Regardless of the symptoms present, subclinical hypothyroidism is also associated with cognitive function problems in both children and older adults, increased risk of cardiovascular disease, and infertility. Patients with subclinical hypothyroidism who present with these conditions are more likely to be treated with prescription levothyroxine, or thyroid replacement therapy 3 5. But health providers should evaluate their patients carefully because levothyroxine therapy is often not helpful for subclinical hypothyroidism 6 7. Even when other conditions are present, natural approaches, including diet and lifestyle changes and working on gut health, often make sense to consider first. 

Subclinical hypothyroidism can present at any age, from young children to the elderly. However, it is much more commonly diagnosed in older adults (since TSH levels naturally increase with age) and in people with cognitive function problems, cardiovascular risk factors (like high blood pressure and cholesterol levels), and fertility issues. Therefore, appropriate diagnosis and treatment may vary based on your age and the severity of your TSH elevation 8 9. 

Even though different people often have different thyroid hormone levels from each other, each individual’s normal levels are set by their pituitary gland and shouldn’t vary much until they become an older adult 2.

For example, someone younger than 60 with a TSH level between 4.5 and 10 might deserve a subclinical hypothyroid diagnosis, whereas an 80-year-old with TSH levels in that range probably does not. In fact, an appropriate TSH level for someone in their 60s might be around 6, while in their 70s a TSH of 7 is normal, and so on, adding a point for each decade of age. 

This means that someone in their 80s with a TSH of 8 is within the standard reference range for a subclinical hypothyroidism diagnosis for someone under 60, but not for someone in their 80s. Therefore, an older adult with above-standard elevated TSH levels may be normal and not have subclinical thyroid disease, so it’s important to be careful with diagnostics and treatment. If we get better at recognizing the age-related differences in serum TSH, the prevalence of diagnosed subclinical thyroid disease may go down.

Find the Root Cause of Subclinical Hypothyroidism

If your thyroid labs suggest subclinical hypothyroidism, it’s important to know why if you want to treat mildly elevated thyroid hormone levels effectively. In the course of treating hundreds of patients with thyroid dysfunction, I can say that subclinical hypothyroidism usually comes down to one or more of these root causes:

• A transient insult to the body, like a period of high stress, that will resolve itself with a little time 
• Gut health issues, like SIBO, causing chronic inflammation throughout the body, including the thyroid gland
• A dysregulated immune system or autoimmunity, such as Hashimoto’s thyroiditis, which may eventually lead to overt hypothyroidism
• Some other cause of chronic inflammation, such as eating an inflammatory diet or dealing with relentless stress
• A genuine problem in the thyroid gland causing poor regulation of thyroid-stimulating hormone
• Pregnancy or infertility 

Addressing one or two of these issues is usually enough to get your elevated TSH levels back in healthy (euthyroid) range without resorting to levothyroxine therapy. 
However, people with subclinical hypothyroidism who are pregnant or struggling with infertility are a different story and typically benefit from thyroid hormone replacement medications 5 10.

For everyone else with subclinical hypothyroidism, what we don’t want to do is “force” your thyroid hormone levels back into the normal reference range with prescription thyroid hormone replacement. Doing that tends to cover up the root cause behind mild abnormalities in your TSH levels. Not to mention, doing thyroid replacement therapy when you don’t need it can compromise your thyroid gland’s normal functioning and make you feel worse.

Finding those root causes is imperative for treating subclinical hypothyroidism. If we just jump straight to replacement therapy, we’re creating a bigger problem that has to be fixed down the line. 

How to Treat Subclinical Hypothyroidism 

Subclinical hypothyroidism is one the few conditions where I can see an advantage to the conventional healthcare approach to its treatment (i.e. first, wait and see) 11. In fact, our approach to treatment at the clinic aligns more with the American Thyroid Association’s approach 2 than it does with the functional medicine approach, which often involves prescribing thyroid hormone replacement when it isn’t needed. Here’s the order of operations I follow when addressing subclinical hypothyroidism:

1. Wait and see. Often, irregular labs will resolve themselves if given a little time 12. This is usually the case with subclinical hypothyroidism, especially if the patient optimizes their diet, sleep, and stress in the meantime. 
2. If other seemingly “unrelated” issues (such as gut dysbiosis) are present alongside the irregular thyroid hormone levels, address these before follow-up testing the hormones in 2–3 months.
3. If the gut or other issues are addressed but TSH levels are still elevated, a true thyroid hormone deficiency may be at play. Consider thyroid hormone replacement therapy as a treatment option.
4. Where associated situations like infertility or pregnancy are a concern, thyroid medication may also be warranted earlier in the treatment course 5 10. However, it’s important to consider other potential root causes of any thyroid imbalance. 

Except in select rare cases, I don’t immediately prescribe thyroid hormone (levothyroxine therapy) for subclinical hypothyroidism. We have a lot of evidence to suggest that it isn’t effective and has no clear benefit in patient outcomes 6 7. Sometimes patients feel even worse when taking levothyroxine 13. I’ve lost count of how many patients have come to see us at the clinic after taking T4 or T3 medication for a while without seeing their symptoms of hypothyroidism improve. At that point, we really want to see what else might be going on. 

But two situations typically warrant thyroid hormone replacement therapy for a short period of time: infertility or pregnancy-induced subclinical hypothyroidism 5 10. If that’s your situation, diet and nutritional supplements may provide valuable support for your thyroid gland and help your gut absorb your replacement therapy medication. When your gut works well, it’s easier to get the most benefit from the lowest dose of medication 14 15 16.

Thyroid Function Tests Offer Transient Insights

I can’t emphasize this enough: your thyroid lab markers only offer a snapshot of your thyroid health at any given point in time. Your results are never a permanent indicator of thyroid dysfunction. Too often, functional medicine practitioners quickly prescribe thyroid hormone replacement when it isn’t necessary, leaving the patient stuck on synthetic thyroxine (T4) or triiodothyronine (T3) for months, years, or even a lifetime. 

But this doesn’t have to be the case. If your thyroid hormone levels indicate subclinical hypothyroidism, retest in 2–3 months: Your thyroid function tests will often normalize on their own 12. And if they don’t, read on to learn about various nutritional and lifestyle interventions that may correct mild thyroid hormone abnormalities without thyroid replacement therapy. 

Treatment of Subclinical Hypothyroidism With Diet and Lifestyle

Often what we need to do in order to normalize thyroid hormone levels in subclinical hypothyroidism is decrease inflammation in the thyroid gland. What’s great is that we can usually accomplish this with diet and lifestyle modifications. If you have subclinical hypothyroidism, read on for some avenues you can try before you consider thyroid hormone replacement medication. 

Optimize Your Health Foundation

First, you’ll want to go back to basics: optimizing your diet, sleep, stress, and movement. This will look different for everyone, but generally following these principles throughout the week will go a long way toward decreasing inflammation in the body and reducing any thyroid dysfunction: 

• Eat an anti-inflammatory diet
• Prioritize good sleep hygiene
• Incorporate regular exercise 
• Practice stress relief

For many people, instating these basics can be enough to get elevated TSH levels back down to their normal range. But if you adopt the basics for a few months and still need to improve your serum TSH by a few points, a couple of nutritional supplements may further support your thyroid gland. 

Selenium and Inositol

We have good evidence to show that selenium (a dietary mineral) and inositol (a sugar made in the body and in some foods) can reduce thyroid dysfunction and put elevated TSH levels back in a healthy reference range. Some studies suggest that selenium on its own can be an effective treatment for subclinical hypothyroidism, but most research shows that combining it with inositol is even better for supporting the thyroid gland 17 18 19. 

For example, a study compared selenium alone with a selenium-inositol combo in 168 patients with subclinical hypothyroidism (their serum TSH levels were between 3 and 6 mIU/L). Compared with the control group that received neither supplement, those who took selenium alone or with myo-inositol (a common form in supplements) had significantly lower TSH levels and better quality of life. However, the reduced TSH levels appeared much faster and to a greater degree in those who took combination therapy 20. 

Another study looked at how selenium with inositol affected thyroid hormone levels in people with autoimmune hypothyroidism (Hashimoto’s), without elevated TSH levels. The combined selenium and inositol significantly reduced their risk of developing overt hypothyroidism (TSH above 10 mIU/L). The treatment also decreased antithyroid antibodies, effectively calming the immune system’s attack on the thyroid gland 21. 

Alongside your health foundations, selenium and inositol are great therapies to try for several weeks before considering thyroid hormone replacement therapy. 

Subclinical Hypothyroidism and Gut Health

If you have subclinical hypothyroidism, another area to explore in addition to nutritional treatment options is your gut health. This is especially important if you have gut-related symptoms, like constipation, diarrhea, bloating, or the like, in addition to subclinical hypothyroidism. The gut and thyroid gland are closely linked, so poor gut health may impact your thyroid hormone levels and vice versa. Often when gut health is improved, the thyroid gland will normalize too.

Some people’s gut issues, such as irritable bowel syndrome (IBS) or small intestinal bacterial overgrowth (SIBO), may resolve with dietary changes, but many others will need additional support. For example, supplements like probiotics and possibly antimicrobials can help correct any dysbiosis (imbalanced gut flora). You can also take steps to support the vagus nerve (which controls digestion, heart rate, and immune system function) to improve the way food moves through your digestive tract. Improving digestion can go a long way toward improving thyroid hormone levels.

In the clinic, we have found time and time again that underlying gut issues often cause symptoms of hypothyroidism. Check out Paige’s story about how addressing her gut health with diet changes and a few key supplements helped significantly reduce her symptoms of overt hypothyroidism and improve her quality of life. The good news is that when we fix the gut, the thyroid gland often normalizes as well.

For more guidance on how to help your thyroid gland and normalize TSH levels by addressing your gut health, I invite you to check out our self-paced thyroid course.

Double Check Whether You Need Levothyroxine Therapy 

Except for pregnant women and some cases of infertility, it’s important to save thyroid hormone replacement as a second (or third or fourth) option when considering treatment of subclinical hypothyroidism. If your mildly elevated TSH level doesn’t simply resolve itself with follow-up thyroid function tests, it’s time to look at several other possible root causes, including gut dysbiosis and nutritional deficiencies before resorting to thyroid replacement therapy.

If you have thyroid hormone levels that indicate subclinical hypothyroidism, and you’ve been told to take levothyroxine, you may consider getting a second opinion. If you feel so inclined, we at the Ruscio Institute for Functional Health can double-check your labs and symptoms to help you find the root cause of your subclinical hypothyroidism and the best ways to treat it.

In the meantime, you can learn more about subclinical hypothyroidism, overt hypothyroidism, hyperthyroidism, gut health, and more through my YouTube channel. And if you’d like a comprehensive guide to balancing your gut health, check out my book, Healthy Gut, Healthy You.

The Ruscio Institute has developed a range of high-quality formulations to help our patients and audience. If you’re interested in learning more about these products, please click here. Note that there are many other options available, and we encourage you to research which products may be right for you.