11 Reasons for Low Thyroid Function

How often have you heard a client say, "I have a slow thyroid"? Did you do an inward eye roll, thinking it was just another excuse to shirk exercise? Well, it’s possible your client isn’t being hyperbolic. An estimated 20 million Americans have some form of thyroid disease, and women are five to eight times more likely than men to be affected (ATA 2016). In fact, statistics show that 1 in 8 women will be diagnosed with a thyroid condition in her lifetime, and the prognosis worsens with age. Females over 60 are more likely to struggle with signs of thyroid dysfunction (NIDDKD 2013).

Classic symptoms of low thyroid function include fatigue, brain fog, weight gain, cold hands and feet, sluggish bowels, depressed mood, cognitive decline and low vitality (Longo et al. 2012). Unfortunately, even though someone may notice symptoms, blood-test results may still be within normal ranges. Modern medicine is geared to diagnosing full-blown pathology, so people often have to wait until a disease progresses to get help, rather than leveraging the "squeaky wheel" and preventing the disease in the first place.

This article provides an overview of the thyroid and its function and explores 11 potential reasons a person may be having thyroid-related challenges. The research presented here is for informational purposes only, and fitness professionals should always stay within their scope of practice and not diagnose.

The Thryoid Gland

Let’s take a closer look at the structure and function of the thyroid gland. It is a butterfly-shaped gland at the base of the neck that acts as a "bellweather" for all bodily functions. It sets metabolism, controls body temperature and ensures that systems are running smoothly. The thyroid produces two key hormones that affect every cell in the body: thyroxine (also called T4) and triiodothyronine (also called T3) (Longo et al. 2012).

The T4 hormone accounts for more than 80% of the hormone produced by the thyroid gland, but T4 must be converted into the "active" T3 form to get inside cells and exert its positive benefits (McNabb 1995). If the thyroid is running smoothly, metabolism and mood will too. On the other hand, if the gland is sluggish, so too will be weight loss and health goals.

The brain ultimately controls thyroid hormone output by releasing thyroid-stimulating hormone (TSH), which "instructs" the thyroid to ramp up hormone output. If someone has a frank hypothyroid condition, lab tests will reveal high TSH levels (i.e., the brain is telling the thyroid to do more work) but low T4 hormone output (i.e., the gland is not complying). This individual is likely already on medication.

However, many people fall between the cracks. A person can have thyroid hormone levels within "normal" ranges (at the outer limits) and still struggle with many or all of the symptoms of low thyroid function. The medical term for this scenario is a subclinical thyroid condition, commonly referred to as thyroid dysfunction. The gland is working, but "roadblocks" are preventing the hormones from exerting their positive impact. Eleven of the most common roadblocks are detailed below, and can be grouped into three general root causes: stress, hormone imbalance and nutrient deficiency.

1. High Blood Sugar

Consumption of processed sugars and carbohydrates has been steadily increasing over the past five decades (Johnson et al. 2007). The effects on blood sugars, insulin and thyroid function are profound. Insulin is the blood sugar hormone, and when everything is running smoothly, the body pumps out just the right amount to pull carbohydrates from the bloodstream and into cells. When people overindulge in high-carb breakfasts, sugary drinks and sweet treats, insulin function worsens, requiring the body to pump out greater amounts of insulin. Over time, this leads to insulin dysfunction and, if left unabated, insulin resistance and diabetes.

One in every two people in the United States has either diabetes or prediabetes, and studies show a much higher incidence of thyroid dysfunction among people with type 2 diabetes compared with those who are free of the disease (Menke et al. 2015; Kadiyala & Okosieme 2010). This thyroid dysfunction is likely due to blood sugar highs and lows that cause increased release of the catabolic cortisol stress hormones that help to control blood sugars. Eventually, this has negative impacts on the brain and on the pituitary gland’s release of TSH (Rettori, Jurcovicova & McCann 1987), and a perpetual cycle can develop—high blood sugar leading to slower thyroid function (compromised metabolism) and subsequent weight gain, which then worsens blood sugar control and thyroid function (Knudsen et al. 2005).

A client who is struggling with symptoms of low thyroid function must make balancing blood sugars and insulin a top priority. One way to quickly and effectively restore blood sugar balance is to reduce intake of processed carbs and simple sugars (Ballard et al. 2013). Once blood sugars and insulin are back on track, supporting a healthy thyroid becomes easier. Note: Many people believe that taking thyroid medication will be a "quick fix." However, a recent study found no weight loss benefit for clients with thyroid dysfunction when they added a thyroid medication (Pearce 2012).

2. The State of Being Overweight or Obese

While insulin dysfunction is the leading cause of diabetes, it’s not inherently the leading cause of obesity. Currently, obesity rates are increasing at 1% per year across the globe, while diabetes is increasing at 4% per year (Lustig 2016). If insulin dysfunction caused obesity, then both rates of diabetes and insulin dysfunction should be increasing at the same rate.

The satiety hormone leptin plays a major role in obesity and is produced by fat cells to signal the brain "I am full," thus putting the brakes on sugar cravings. However, a Western diet, poor food choices, insulin dysfunction and stress can all scramble this leptin signal to the brain, leading to constant cravings (Macedo & Diez-Garcia 2014). Unfortunately, the cravings are rarely for grass-fed beef and broccoli, but rather for processed carbs and simple sugars.

Leptin dysfunction goes hand in hand with both diabetes and obesity, but research also suggests a strong association with thyroid dysfunction as well (Zimmerman-Belsing et al. 2003). An overweight or obese client will need to shed body fat, in particular the pro-inflammatory visceral fat around internal organs, in order to bring the thyroid back into balance.

While in theory clients need to run a caloric deficit to lose weight, the general advice from doctors to patients with subclinical thyroid condition—"Eat less; move more"—is not specific enough to help people achieve real progress. In fact, it often makes things worse! Following a strict calorie-controlled diet (typically low in fat) and increasing exercise volume (typically with steady-state cardio) can leave a person spinning his wheels, not losing weight and—even worse—gaining more weight!

3. Chronic Inflammation

Research is clear: In a person with obesity or excess weight, the body is on fire! That’s right: With weight gain and insulin dysfunction, systemic and chronic inflammation takes root as white adipose tissue—that visceral fat surrounding the organs—increases and produces proinflammatory cytokines (Pang et al. 1988). A state of inflammation impairs thyroid function.

Inflammation reduces thyroid hormones in the short term and negatively influences thyroid receptors in the long term (Kimura & Caturegli 2007). Chronic inflammation, seen in clients who are overweight and struggling with digestive problems or autoimmunity, also impairs the body’s ability to convert T4 hormone into T3 (Molnar et al. 2002).

Systemic inflammation arises from many different root causes, including weight gain, digestive problems, autoimmune conditions, too much exercise, etc. It’s therefore critical to take a holistic approach and improve all areas of health to mitigate inflammation. Encourage clients to work with a medical professional to correct any digestive dysfunction (gas, bloating, constipation, irritable bowel syndrome, etc.) because the gut is the "engine" of the body and home to more than 70% of the immune system (Vighi et al. 2008), which triggers the inflammatory response.

4. Stress

Stress is a major underlying root cause of thyroid dysfunction. In today’s 24/7 society, we’re constantly connected and on the go. While this can be fantastic for productivity, it takes a toll on the brain and, ultimately, the thyroid. The stress response begins in the brain, which then acts on the pituitary gland, and this in turn relays messages to the rest of the body. If we "wear out" the thyroid gland with long, busy workdays and never-ending assaults of emails, texts and social media updates, its function begins to slow, resulting in less thyroid-stimulating hormone. Less TSH output by the brain means less thyroid hormone output, leading to fatigue, weight gain and low mood.

As discussed above, this chronic stress produces blood sugar highs, followed quickly by blood sugar lows that necessitate even more cortisol output to stabilize blood glucose. This constant output of cortisol places a heavy burden on the pituitary gland, thus reducing TSH output (Rettori, Jurcovicova & McCann 1987).

In this scenario, blood tests would show that TSH and T4 levels were "low normal" (low, but not likely low enough to be outside normal range and signal a red flag). However, many common symptoms of low thyroid function would be present. The solution: Restore resiliency by reducing stress levels. Limit phone use, spend more time in nature, and eliminate all stimulants such as coffee for at least 1 week.

5. The Liver Is Working Overtime

Most people are unaware that thyroid hormones produced by the thyroid gland must be "activated" before they can benefit the body (Longo et al. 2012). A large amount of this activation (over 60%) happens in the liver; therefore, if the liver is working overtime, thyroid function may struggle. For example, a diet high in sugar and processed carbs, high alcohol intake, high coffee consumption or environmental toxins all have a significant deleterious effect on the liver and, ultimately, on thyroid hormones.

An obese client with poor blood sugar control will be more prone to compromised liver health and fat accumulation in the liver (Moreno-Navarette et al. 2012). A nightly alcoholic drink, or worse, binge drinking on the weekends, is also taxing on liver detoxification pathways (called phase I and phase II). Coffee addiction (multiple cups daily) imposes a burden to phase I liver detoxification as well. And the environment plays a major role, with daily exposure to toxins in air, water and food (pesticides, herbicides, etc.) increasing the liver’s workload. All of these factors may impair liver function and thus reduce the conversion of T4 hormone to the active T3 form.

It’s easy to appreciate the interconnectedness and impact of blood sugar imbalance, weight gain, stress, inflammation and poor liver function on the thyroid. While this combination may not trigger frank hypothyroid disease in the short term, it can easily impair healthy thyroid function and leave a client tired, rundown and stuck in a weight gain cycle.

6. Gut Imbalance

The balance of "good" to "bad" bacteria in the gut also plays a role in the activation and utilization of thyroid hormones. Approximately 20% of thyroid hormone conversion takes place in the belly, so if too many "bad" gut bacteria set up shop, thyroid hormone conversion becomes difficult (Strakis & Chrousos 1995). Low thyroid function is strongly associated with digestive problems and can quickly become a vicious cycle, each making the other worse.

It doesn’t help that our food choices are typically high in processed carbohydrates and sugars, while at the same time being low in fiber. This creates the ideal conditions for intestinal dysbiosis (too many "bad" bacteria). Gut bacteria, collectively known as the microbiome, communicate and interact with the rest of the body. New research highlights their potential for triggering strong cravings for sugar; this is especially true of the bacteria family fermicutes, which can produce sugars 100 times more effectively than other gut bacteria, prompting intense sugar cravings (Brown et al. 2012). This may trigger the downward spiral of blood sugar imbalance, weight gain, inflammation and thyroid dysfunction.

You can encourage your clients—with the help of a registered dietitian—to reboot their gut health by reducing carbohydrate intake (breads, pastas and processed carbs); eating more fiber-rich foods like vegetables and fruit; and adding naturally fermented foods like yogurt, kefir, sauerkraut and kimchee, to provide friendly bacteria. A supplemental probiotic may also help to restore gut-bacteria balance.

7. A Leaky Gut

Autoimmune diseases are rapidly increasing—50 million Americans suffer from some type of autoimmune disease today (AARDA 2016)—and autoimmune thyroid conditions are the most common form of autoimmune disorder, affecting approximately 7%–8% of the population (Betterle & Zanchetta 2003).

An autoimmune condition occurs when the immune system starts attacking the body (in this case the thyroid gland), leading to tissue destruction and impaired glandular function. If left unchecked, the disorder will eventually destroy the gland or organ. Autoimmune conditions may be present for 5–10 years before any symptoms show up (Kharrazian 2012) and, since a typical thyroid lab-test screen doesn’t include the test for autoimmune thyroid disease, it’s often missed until significant damage sets in.

How does this connect with the gut? Well, as mentioned in the Chronic Inflamation section, over 70% of the immune system is located in the gut, and experts now believe that all autoimmune diseases—whether they affect the pancreas (as in type 1 diabetes), the nerves (as in multiple sclerosis) or the thyroid gland (as in Hashimoto’s disease)—are rooted in the digestive tract (Campbell 2014). The balance of bacteria in the large intestine (microbiome) has an intimate connection with the immune system. If the balance of "good" to "bad" bacteria gets thrown out of whack, it may damage the gut wall and allow the passage of bacteria, viruses and undigested proteins into the bloodstream, triggering an unnecessary immune response.

This condition is commonly known as leaky gut (or intestinal hyperpermeability) and has been identified as a common feature in people with autoimmune thyroid disease (Fasano 2012). When dysbiosis or zonulin dysfunction (zonulin is a protein that modulates gut permeability) damage the tight junctions holding gut cells firmly together, the stage is set for a leaky gut and an overactive immune system.

A leaky gut overburdens the immune system and predisposes some people to an autoimmune condition. A leaky gut also triggers an inflammatory response from the immune system, which may further exacerbate thyroid dysfunction. Restoring gut-
bacteria health and the integrity of the gut wall is a top priority for anyone struggling with symptoms of low thyroid function.

8. Too Much Exercise

Typically, people who complain about symptoms of low thyroid function to their doctors, but have normal lab tests, are told to exercise more to resolve weight gain. Unfortunately, this is often poor advice because it doesn’t improve the quality of exercise, and ramping up volume in an attempt to chase caloric burn is inefficient.

If a client always performs the same steady-state cardio workout (typically at the same moderate intensity) for days, weeks and months on end, her body will adapt to the training stress after 4–8 weeks. If she continues with this type of training, she’ll actually burn fewer calories, not more (Boutcher & Dunn 2009).

Worse yet, scheduling additional days of the same type of training will stress the nervous system and increase cortisol output, which also impairs healthy thyroid function (Walter et al. 2012). In short, the "more is better" approach to exercise for weight loss just digs a deeper hole.

To trigger fat loss and get the thyroid back in balance, you need to shorten the duration of exercise bouts and increase the intensity. Try programming 4–6 sets of 100-meter sprints in a park (rest 90 seconds between sprints), or do Tabata-style training (20 seconds on, 10 seconds off, for 6–8 rounds). Another option is to lift heavier weights to add strength and lean muscle. Reducing training volume and increasing intensity is a great way to get the thyroid back on track.

9. Iodine Supplementation

Many clients who struggle with cold hands and feet, sluggish bowels, low mood and weight gain have likely been told by health food store employees that iodine is great for boosting thyroid function. While this is true for some people, for others it can actually worsen an autoimmune thyroid condition (Mazziotti et al. 2003).

Supplemental iodine is one of the most researched factors that contribute to autoimmune thyroid conditions, but because very few people get tested for the anti-thyroid peroxidase (TPO) antibodies that would diagnose an autoimmune condition, iodine supplementation is rampant and may be making things worse. Suggest to clients that they get a professional medical opinion before supplementing.

Clients concerned about sluggish thyroid function should ask their doctor for a full thyroid hormone panel that includes TSH, free T4, free T3 and anti-TPO antibodies. Thyroid peroxidase is the enzyme responsible for making thyroid hormones, and if anti-TPO levels are elevated, it will confirm that the immune system is attacking this enzyme, leading to subpar thyroid hormone output and potential thyroid damage.

10. Low Selenium Levels

If lab tests reveal only mildly elevated TSH levels and normal T4, it’s likely the thyroid problem is "downstream" of the thyroid gland. Since the T4 hormone must be converted into the active T3 to exert its positive effects on mood, metabolism and mental clarity, a person who is deficient in essential minerals like selenium that are required for the conversion will struggle with a sluggish thyroid.

The deiodinase enzyme requires selenium in order to remove one iodine molecule from T4 and transform it into T3. It’s therefore very important to get the right amount of selenium.

The Recommended Dietary Allowance (RDA) for selenium is 50–55 micrograms per day for men and women (Institute of Medicine 2000). However, that is the amount required to fight off disease, not necessarily to promote health. The body uses selenium as an antioxidant and in the formation of glutathione (an important antioxidant within cells); therefore, if a person is struggling with low thyroid function, then inflammation and excess burden on the liver may be depleting her selenium levels.

The goods news is that it’s quite easy to get more than the daily dose of selenium. Brazil nuts are far and away the richest dietary source of selenium, with just two providing over 100 mcg of selenium to support healthy thyroid hormone conversion (USDA 2000). Other great sources include fish—like cod, salmon, tuna and halibut—as well as shitake and crimini mushrooms.

11. Low Vitamin D Levels

Vitamin D is important for the formation of thyroid hormones and the body’s ability to take up thyroid hormone. A client who struggles with frequent colds and flu, chronic inflammation and irregular sun exposure, or who lives in a city with a true winter climate, will likely have low vitamin D levels, which will negatively affect thyroid health.

Vitamin D also plays a key role in keeping the immune system in balance and boosting production of regulatory immune cells that help to prevent autoimmune reactions (Holick 2004). Research shows a strong association between autoimmune thyroid conditions and low vitamin D levels (Smith et al. 2000). In fact, if a client’s vitamin D levels are low and he suffers from an autoimmune thyroid condition, it may reduce his production of antibodies (Deluca & Cantorna 2001).

Foods like egg yolks, pork and mushrooms contain vitamin D, but they’re not enough to keep levels up through the winter months. The sun is far and away the best source of vitamin D; therefore, anyone who struggles with thyroid dysfunction may benefit from taking a supplement during the winter months.

Heed the "Dysfunctional Dashboard"

The thyroid is like the dashboard on a car that indicates when it’s time to refill the gas tank or top off the oil. Unfortunately, most people don’t watch for the early signs of dysfunction (or don’t know what those signs are). Blood sugar and insulin imbalance, weight gain, excess inflammation and stress, digestive dysfunction and nutrient deficiencies are all very common, and they can keep the thyroid stuck in the mud rather than running on all cylinders. Educate clients to incorporate the right fixes, in consultation with appropriate medical advisers, and help people get their health back on track.