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What Causes Hypothyroidism?

The most common cause of hypothyroidism is Hashimoto's Thyroiditis.
What Causes Hypothyroidism?

Hypothyroidism, or underactive thyroid disease, occurs when the thyroid gland doesn’t produce enough thyroid hormone. Thyroid hormones impact every cell in the body and are critical to the body’s ability to utilize energy from food. When the body doesn’t produce enough thyroid hormones, many of its systems (such as heart rate, body temperature, and metabolism) slow down. That’s why one of the first signs of hypothyroidism is a feeling of sluggishness or fatigue.

There are several known causes of hypothyroidism, but there is also a lot of debate regarding what combination of genetics, illness, and environmental factors may cause someone to develop the disease. Below are a few categories of potential causes of hypothyroidism.

Autoimmune Disease

The most common cause of hypothyroidism is Hashimoto’s disease, a condition in which the body produces antibodies that attack the thyroid gland. Hashimoto’s is an autoimmune disease, which may be brought on by a combination of genetics and environmental triggers.

People who already have an autoimmune disorder, such as rheumatoid arthritis, type I diabetes, or Celiac disease, are more likely to develop another autoimmune disorder (called polyautoimmunity) like Hashimoto’s disease. Additionally, people who have a close relative with autoimmune disorders are more likely to develop hypothyroidism due to Hashimoto’s disease.

Previous Thyroid Disease

Another cause of hypothyroidism might be previous experience of and treatment for hyperthyroidism. The various treatments for hyperthyroidism could leave the thyroid short on thyroid hormones the body needs.

These treatments for hyperthyroidism include:

  • Surgery to remove part of the thyroid
  • Radioactive iodine treatment
  • Hyperthyroid medication such as Propylthiouracil (PTU)

Receiving radiation therapy in the neck or chest area may also damage the thyroid gland, resulting in hypothyroidism.

Underlying Issues

There is an alternative way of viewing health and illness that many functional medicine and holistic health practitioners champion. This line of thinking says that when there is illness in the body, it’s worthwhile to investigate whether there are underlying reasons for the illness. For example, if blood tests indicate that the body is producing antibodies that target the thyroid, as in Hashimoto’s disease, an alternative practitioner would question what might have triggered the body to do so.

When it comes to causes of hypothyroidism, some functional and alternative medicine theories include:

  • Food sensitivities
  • Impaired stress response
  • Intestinal permeability (leaky gut syndrome)
  • Environmental toxins
  • Post-traumatic stress disorder

Not everyone subscribes to the philosophy of treating illness in this way, but according to the World Health Organization, over eighty percent of countries worldwide practice traditional (meaning age-old medicine particular to a certain culture) or complementary (alternative) medicine, in addition to Western medicine. So, it may make sense to keep an open mind when looking to understand and treat illness.

In addition to the above causes, other risk factors for hypothyroidism include:

  • Being female, particularly during and after pregnancy and menopause
  • Having Caucasian or Asian ancestry
  • Having certain genetic disorders such as Down’s syndrome
  • Having bipolar disease

Whatever the reason someone develops hypothyroidism, there are several symptoms that may point towards this diagnosis. Symptoms include:

  • Fatigue (the most common symptom)
  • Dry skin and hair
  • Hair loss, including thinning eyebrows
  • Sensitivity to cold
  • Unexplained weight gain
  • Depression
  • Joint pain or carpal tunnel syndrome
  • Trouble with memory or “brain fog”
  • Vocal hoarseness
  • Puffiness in the face
  • Heavier periods, increased levels of cramping during menstrual cycle

Use our symptom tracker to see how likely you are to have hypothyroidism:

The tricky thing about hypothyroidism is that a lot of its symptoms mimic other conditions, particularly depression. In fact, a high percentage of people diagnosed with anxiety and depression actually have an undiagnosed thyroid condition. If you have one or more of the above symptoms, it’s worth seeing a doctor and getting a blood test to determine if your thyroid is functioning properly.


If it’s been determined that you do have hypothyroidism, the most common method of treatment is a synthetic form of thyroxine hormone (T4). T4 is the storage hormone and must be converted by the body into active T3 to be used by cells. Whether in generic (levothyroxine) or brand-name (Synthroid) form, the synthetic hormone mimics the thyroxine, or T4, that your body is lacking.

We are all unique with individual sensitivities. Our bodies will not all react the same way to a specific medication or dosage. Your doctor will take into account your age, weight, gender, severity of symptoms, and blood test results.

We believe in a gentle start to dosing. This slow, step-by-step method of reaching your optimal dose is easier on the body than the “sock it to me” approach so characteristic of our fast-paced culture.  

Thyroid hormone replacement drugs are powerful. This is why it is critical to be under careful medical supervision when on these drugs, especially when starting a new brand or increasing dosage level.

For more information about treatment options, visit our Medications page.

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