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Why do I have hypothyroidism?

Hypothyroidism, also called underactive thyroid or low thyroid, is a disorder of the endocrine system in which the thyroid gland does not produce enough thyroid hormone. It is a common condition that affects approximately 5% of the general population, and is 10 times more likely to impact women than men. Thyroid hormone regulates metabolism and plays an essential role in growth, development and many physiologic processes. When the thyroid gland fails to produce adequate levels of thyroid hormones, many body functions slow down. Fortunately, hypothyroidism can be easily diagnosed with blood tests and effectively managed with daily oral thyroid medication.

What causes hypothyroidism?

There are several potential causes of hypothyroidism:

  • Hashimoto’s thyroiditis: This is an autoimmune disorder in which the immune system attacks and destroys the thyroid gland. It is the most common cause of hypothyroidism in the United States, accounting for 90-95% of cases.
  • Thyroid surgery: Removal of part or all of the thyroid gland can cause hypothyroidism. This may be done to treat thyroid nodules, thyroid cancer or Graves’ disease.
  • Radiation therapy: Radiation treatment to the neck area, often used to treat cancers like Hodgkin’s lymphoma, may damage the thyroid and cause hypothyroidism.
  • Medications: Drugs like lithium, amiodarone and interferon alpha can negatively impact thyroid function.
  • Congenital hypothyroidism: Some babies are born with an underdeveloped thyroid gland or no thyroid gland at all.
  • Pituitary gland disorders: The pituitary gland produces thyroid stimulating hormone (TSH), which signals the thyroid to make thyroid hormones. Dysfunction of the pituitary gland may disrupt this process.
  • Iodine deficiency: The thyroid relies on iodine to produce thyroid hormones. Low iodine levels, especially during pregnancy and infancy, can impair thyroid function.

In some cases, the specific cause of hypothyroidism cannot be identified. This is known as idiopathic hypothyroidism.

What are the risk factors for hypothyroidism?

Certain factors increase the likelihood of developing hypothyroidism:

  • Being female: Women are 5-10 times more likely to have hypothyroidism than men.
  • Increasing age: The risk rises with age, especially after age 60.
  • Family history: Having a close relative with an autoimmune thyroid disease increases risk.
  • History of hyperthyroidism: People who have had an overactive thyroid are more likely to later develop hypothyroidism.
  • Pregnancy: Hypothyroidism occurs in 0.3–0.5% of pregnancies. Women who develop postpartum thyroiditis have a high chance of experiencing permanent hypothyroidism.
  • Radiation exposure: Past radiation treatment to the chest, neck or head for cancers like Hodgkin’s lymphoma can damage the thyroid and cause hypothyroidism later in life.
  • Treatment with amiodarone, lithium, interferon alpha, interleukin-2, or thalidomide can affect thyroid function.
  • Recent surgery on the thyroid, thyroid area or pituitary gland.
  • Severe iodine deficiency.

What are the symptoms of hypothyroidism?

Symptoms tend to develop slowly over months or years. They may be vague and can overlap with symptoms from many other conditions. Common signs and symptoms include:

  • Fatigue
  • Increased sensitivity to cold
  • Constipation
  • Dry skin
  • Weight gain
  • Puffy face
  • Hoarse voice
  • Elevated blood cholesterol level
  • Muscle weakness
  • Muscle aches, tenderness and stiffness
  • Pain, stiffness or swelling in your joints
  • Heavier than normal or irregular menstrual periods
  • Thinning hair
  • Slowed heart rate
  • Depression
  • Impaired memory

When should I see a doctor?

Consult your doctor if you’re experiencing any persistent symptoms of hypothyroidism, such as fatigue, weight gain, constipation, dry skin, or feeling cold. It’s important to be evaluated because the symptoms of hypothyroidism are common to many other medical conditions. Thyroid blood tests help confirm or rule out the disorder. Testing is particularly recommended for those at increased risk because of family history, other autoimmune diseases, past radiation treatment to the neck area, or taking specific medications.

How is hypothyroidism diagnosed?

Diagnosis of hypothyroidism requires blood tests. The main tests are:

  • TSH test: Measures the level of TSH (thyroid-stimulating hormone). This pituitary hormone regulates thyroid hormone production. Elevated TSH indicates underactivity of the thyroid gland. A TSH over 10 mIU/L is considered highly suggestive of hypothyroidism.
  • Free T4 test: Measures the amount of free (unbound) thyroxine (T4) thyroid hormone circulating in the blood. Low levels confirm hypothyroidism. It may be checked together with TSH for confirmation.

If the diagnosis is uncertain, additional blood tests may be recommended:

  • Free T3 test: Measures free triiodothyronine (T3), the active form of thyroid hormone at the cellular level. Low T3 can help establish hypothyroidism in rare cases of normal TSH.
  • Thyroid peroxidase antibodies: High levels confirm Hashimoto’s autoimmune thyroiditis, the most common cause of hypothyroidism.

How is hypothyroidism treated?

Treatment involves taking daily thyroid hormone replacement medication, usually levothyroxine (Levoxyl, Synthroid, Tirosint, Unithroid, etc). This oral medication restores adequate hormone levels, reversing the signs and symptoms of hypothyroidism. Treatment is continued for life. The dose may need periodic adjustments based on thyroid function testing.

Here is a general overview of hypothyroidism treatment:

  • Blood tests are done regularly to monitor thyroid hormone levels and adjust medication dosing as needed.
  • It may take several months to determine the optimal dose.
  • Symptoms usually start improving within 1-2 weeks after starting medication.
  • Thyroid hormone supplements should be taken on an empty stomach 30-60 minutes before breakfast.
  • Dose adjustments and more frequent monitoring are needed during pregnancy.
  • Treatment is safe for breastfeeding mothers.
  • Most people feel completely normal once on the appropriate thyroid hormone replacement.

In addition to the thyroid medication, your doctor may recommend:

  • Eating foods rich in iodine like seafood, eggs, yogurt and fortified salt, if iodine deficiency contributed to the hypothyroidism.
  • Vitamin D and/or iron supplements if deficient.
  • A diet low in goitrogens (foods like soy, cabbage and broccoli which may interfere with thyroid function) if Hashimoto’s thyroiditis is the cause.
  • Being physically active and maintaining a healthy body weight and diet to prevent cardiovascular complications.

What are the complications of untreated hypothyroidism?

When left unmanaged, hypothyroidism can cause a number of health problems over time:

  • Goiter: Enlargement of the thyroid gland as it struggles to produce more hormones.
  • Heart problems: An underactive thyroid causes a slower heart rate and increase in bad (LDL) cholesterol, raising the risk of heart disease.
  • Mental health issues: Hypothyroidism can contribute to depression, anxiety and other mental health disorders.
  • Peripheral neuropathy: Numbness and tingling in the arms and legs due to nerve damage.
  • Myxedema: Intense cold intolerance and drowsiness followed by profound lethargy and unconsciousness due to longstanding, undiagnosed hypothyroidism.
  • Infertility: Poorly controlled hypothyroidism can affect ovulation and fertility.
  • Birth defects: There is an increased risk of birth defects with untreated hypothyroidism in pregnant women.

That’s why it’s important to properly diagnose and treat hypothyroidism before complications arise.

What is subclinical hypothyroidism?

In some people, TSH levels are slightly elevated while free T4 levels remain normal. This indicates mild thyroid underactivity known as subclinical hypothyroidism. The thyroid is only mildly underactive and thyroid hormone levels are within the normal range. Symptoms are usually mild or nonexistent.

Here is an overview of subclinical hypothyroidism:

  • Causes are the same as overt hypothyroidism – Hashimoto’s thyroiditis being the most common.
  • Occurs in 4-10% of the population but is more common in older women.
  • Many cases resolve spontaneously or do not progress over time.
  • Associated with an increased risk of developing overt hypothyroidism in the future.
  • Treatment with thyroid hormone may be considered in certain cases, such as TSH over 10 mIU/L or high thyroid antibodies.

Monitoring TSH and free T4 levels determines if treatment becomes necessary. In most cases, it’s reasonable to retest in 6-12 months.

Can hypothyroidism be prevented?

While you can’t prevent hypothyroidism from autoimmune Hashimoto’s thyroiditis, the most common cause, the following practices may help lower your risk:

  • Avoid iodine deficiency by eating iodine-rich foods like seafood, eggs, yogurt and iodized salt.
  • Be aware of goitrogenic foods like soy, broccoli and cabbage. Limit intake if you have Hashimoto’s.
  • Treat other autoimmune conditions, which increase the risk of Hashimoto’s thyroiditis.
  • Maintain a healthy body weight.
  • Manage stress levels.
  • Avoid radioactive iodine exposure.
  • Use protective gear like lead aprons when exposed to x-rays.
  • Advocate for safe radiation practices if you require imaging or cancer treatment.

While we can’t always prevent hypothyroidism, we can detect and treat it early before complications occur. Following a healthy lifestyle provides the best chance of staying well.

What is the outlook for hypothyroidism?

With proper treatment, most people with hypothyroidism can expect an excellent outcome. Symptoms improve within weeks of starting thyroid hormone replacement. Most people are able to keep their thyroid levels in the normal range with long-term medication and monitoring. It’s important to take thyroid medication consistently, get bloodwork as recommended, and attend all follow up appointments. With treatment, people with hypothyroidism can maintain a high quality of life.


In summary, hypothyroidism is a common condition where the thyroid gland does not make enough thyroid hormones. Hashimoto’s thyroiditis is the most frequent cause. Symptoms like fatigue, weight gain and feeling cold tend to develop slowly over time. Blood tests measuring TSH and free T4 help diagnose hypothyroidism. Treatment involves daily thyroid hormone replacement medication which relieves symptoms and prevents complications. With proper management, hypothyroidism can be well controlled in most people. Remaining aware of your thyroid health, taking medication as directed, and sticking to regular monitoring will help ensure you continue feeling your best.