The Underlying Causes of Thyroid Disease

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Do you see a lot of patients with thyroid disorders? The number of people suffering from thyroid disorders continues to rise each year. Read on to learn more about thyroid disorders and how to address the root cause of disease.

The American Thyroid Association estimates that 20 million Americans have some form of thyroid disease, and up to 60 percent of these people are unaware of their condition. One in eight women will develop a thyroid disorder during her lifetime (1). As of 2014, levothyroxine, a synthetic form of thyroid hormone, was the highest-selling drug in the United States (2). Most individuals who take thyroid hormone will never get off the medication.

In this article, I’ll cover the major symptoms of overactive and underactive thyroid, the conventional approach to thyroid treatment, and how addressing the underlying causes of thyroid disorders can reduce, and in many cases eliminate, the need for synthetic thyroid hormones.

What’s so Important about the Thyroid, Anyway?

Every cell in the body has receptors for thyroid hormone. It is responsible for the most basic aspects of our body’s function, impacting all major systems. Thyroid hormone directly acts on the brain, the GI tract, the cardiovascular system, bone metabolism, red blood cell metabolism, gallbladder and liver function, steroid hormone production, glucose metabolism, lipid and cholesterol metabolism, protein metabolism, and body temperature regulation (3).

The Conventional Medical Approach to Thyroid Disorders

In medicine, the key to choosing the best treatment is an accurate diagnosis. If the diagnosis isn’t correct, the treatment will be ineffective—or even cause harm. Unfortunately, misdiagnosis is common in the management of thyroid disorders. If a person visits a doctor with hypothyroid symptoms, she will simply be given replacement hormones without any further inquiry into the cause of her condition. Even worse, if she has hypothyroid symptoms but her lab tests are normal, she’ll be told that she’s “fine.” If the patient insists that she’s not “fine,” she might be sent home with an antidepressant, but with no further clue about the cause of her symptoms.

The problem with this approach is that thyroid physiology is complex. The production, conversion, and uptake of thyroid hormone in the body involve several steps (4). A malfunction in any of these steps can cause hypothyroid symptoms but may not show up on standard lab tests. It is incorrect (and even negligent) to assume that all cases of hypothyroidism share the same cause and require the same treatment, yet that is exactly what the standard of care for hypothyroidism delivers.

Conventional medicine is almost exclusively oriented toward “disease management”: using drugs or surgery to suppress symptoms. In functional medicine, we focus on addressing the underlying cause of disease so that patients can get well and stay well without unnecessary drugs or surgery. Although a prescription for thyroid hormone replacement is sometimes necessary, the first step should always be to determine why the thyroid is malfunctioning in the first place. Sometimes addressing the underlying cause of the thyroid problem is enough to resolve it without resorting to thyroid hormone replacement.

Many conventionally trained clinicians will simply run a TSH test and call it a day. However, this misses critical information you need about your patient’s thyroid metabolism. I always order a combination of thyroid markers, including TSH, T3, T4, free T3, free T4, and thyroid antibodies.

The Underlying Causes of Thyroid Disorders

The two major causes of thyroid disorders are nutrient deficiency and autoimmune disease.

Iodine is a crucial nutrient for thyroid function. Thyroid hormone is rich in iodine, and deficiency of iodine can cause both hypothyroidism and goiter (a swelling of the thyroid gland) (5). Zinc is required for the synthesis of thyroid hormone, and deficiency of zinc has been shown to result in hypothyroidism (6). Selenium, a cofactor for iodothyronine deiodinase, is required to convert T4 (the inactive form of thyroid hormone) into T3 (the active form of thyroid hormone). Selenium deficiency exacerbates conditions caused by inadequate iodine intake (7).

The most common autoimmune cause of thyroid problems is Hashimoto’s disease. In Hashimoto’s disease, the body attacks the thyroid gland, progressively destroying its capacity to produce thyroid hormone and resulting in hypothyroidism (8). Some studies suggest that up to 90 percent of people with hypothyroidism have Hashimoto’s disease (9). Graves’ disease is another autoimmune disease that affects the thyroid gland, but it causes the thyroid to become enlarged and overactive, which results in hyperthyroid symptoms (10).

You can figure out if your patient’s thyroid issues are due to an autoimmune process by testing for thyroid antibodies (thyroglobulin and thyroid peroxidase antibodies). While not all people with Hashimoto’s have hypothyroid symptoms, thyroid antibodies have been found to be a marker for future thyroid disease (9).

(It’s important to note that up to 30 percent of patients with Hashimoto’s do not test positive for thyroglobulin or thyroid peroxidase antibodies. In those cases, a thyroid ultrasound test may be needed to confirm the diagnosis.)

Strategies for Improving Thyroid Function

With all of this in mind, let’s look at dietary, lifestyle, and supplement strategies for addressing nutrient deficiency and autoimmunity, the two primary causes of thyroid disorders.

Dietary considerations:

  • Avoid high amounts of goitrogens, which increase the need for iodine and damage the thyroid gland
  • Consume adequate dietary iodine and selenium
  • Avoid foods that potentially trigger an autoimmune response
  • Avoid very-low-carb diets, which can decrease thyroid function. (Note: this is a general rule and may not apply to all patients. Experimentation is often necessary.)

Lifestyle changes:

  • Manage stress: chronic stress impairs thyroid function at many different levels (11, 12)
  • Heal the gut: 80 percent of the immune system resides in the gut, and gut bacteria assist in converting T4 into T3 (13)
  • Get some sun: sun exposure has been shown to be protective against autoimmune disease (14)


  • Iodine and selenium: most optimal to get from food, but in cases of significant deficiency, supplementation may be necessary
  • Vitamin D: supplementation is required when sun exposure is not sufficient to achieve adequate levels


  1. What are the underlying causes of hyperthyroidism? I was recently diagnosed and feeling miserable!

  2. Hi, thank you for the info! I have recently been diagnosed with Hashimoto’s. My doctor doesn’t seem to know how to treat my Hashimoto, neither does my Endo chronologist. I looked into a functional doctor in my area, and have been unsuccessful in my attempts. Seems as though I have not been able to find a doctor in my area that knows how to manage my Hashimoto. What would be your recommendation for finding a doctor in my area that could help me heal from this Hashimoto disease? I’m really desperate at this point. I have had two surgeries in the last three months. My gallbladder removed, also hysterectomy, miscarriages, a ton of different Gastro problems including pancreatitis,gastroenteritis, stomach infections, goiter and many other hormonal issues.
    If you have any recommendations it would be greatly appreciated thanks again!

  3. After you start taking selenium and iodine how long will it be6before you see a difference, whereas you can start to lose weight or regulate correctly. Any foods in particular I can get these minerals in? The weight doctor said under the LARS test the level was 45.

  4. I started to get pressure on my thyroid when I got my first iphone… now I am sensitive to cell towers and any cell phone that is on and active… I always get a pressure on my thyroid when I go out in public now, I have turned off wifi and bought ethernet for internet, use a landline with cord… NOTHING WIRELESS…. The wireless waves that are being used are disrupting thyroid function… I just was at a store today next to 3 cell phone towers and 2 of the ladies that work there were recently diagnosed to take thyroid meds, one never had this issue until leaving India to here in U.S.