Signs of an Underactive Thyroid

Medically reviewed on Dec 28, 2023 by Jordan Stachel, M.S., RDN, CPT. To give you technically accurate, evidence-based information, content published on the Everlywell blog is reviewed by credentialed professionals with expertise in medical and bioscience fields.

Table of contents

• What is an Underactive Thyroid?
• What are the Symptoms of an Underactive Thyroid?
• What Causes Hypothyroidism?
• How is an Underactive Thyroid Diagnosed?
• How do you treat an Underactive Thyroid?
• What Happens if an Underactive Thyroid Isn’t Treated?
• Detect an Underactive Thyroid at Home with Everlywell Hormone Testing

According to the American Thyroid Association, almost ten percent of society is plagued with an under-active thyroid, and about half of them aren’t aware that they have a thyroid condition [1]. This means approximately fifteen million Americans have an easily diagnosable and correctable disorder that affects weight, energy, and the risk for many other diseases.

What is an Underactive Thyroid?

An underactive thyroid, known as hypothyroidism, is when the thyroid gland (located in the neck) produces insufficient amounts of thyroid hormones – T3 and T4. These hormones are essential for regulating metabolism and energy levels in the body.

What are the Symptoms of an Underactive Thyroid?

Common underactive thyroid symptoms include:

• Chronic fatigue
• Unintentional weight gain
• Sensitivity to cold
• Dry skin and hair
• Mood and memory problems
• Muscle weakness
• Slowed heart rate
• Depression
• Elevated cholesterol levels, increasing risk of heart disease

What Causes Hypothyroidism?

When the thyroid gland doesn't produce enough hormones, it's often due to an impairment in its ability to function normally. This impairment can be caused by a problem within the thyroid gland itself, such as damage to the thyroid cells or an iodine deficiency. Sometimes, the issue stems from the pituitary gland or the hypothalamus, which are areas of the brain responsible for regulating thyroid hormone production. If these regulatory systems are not working correctly, they can fail to signal the thyroid gland to produce the right amount of hormones. Other causes of impaired thyroid function include:

• Autoimmune disease: Such as Hashimoto's thyroiditis, where the immune system attacks the thyroid.
• Thyroid surgery: Thyroid dysfunction can be caused by thyroid cancer, as well as the removal of all or a portion of the thyroid.
• Radiation therapy: Cancer treatment of the head and neck can affect the thyroid gland.
• Medications: Certain drugs, such as lithium, amiodarone, and glucocorticoids can contribute to hypothyroidism [2].
• Pregnancy: Some women develop hypothyroidism during or after pregnancy, known as postpartum thyroiditis.
• Genetics: Some individuals are born with low thyroid hormone levels, known as congenital hypothyroidism.

Additionally, a lifestyle characterized by low activity levels, unhealthy sleep habits and an unbalanced diet is correlated with hypothyroidism. A study published in 2021 suggests that factors such as staying up late on weekends, poor overall sleep quality, and iodine excess are associated with an increased risk of subclinical hypothyroidism, while regular exercise is associated with a lower risk of subclinical hypothyroidism [3].

How is an Underactive Thyroid Diagnosed?

Hypothyroidism is typically diagnosed using a simple blood test, measuring Thyroid Stimulating Hormone (TSH) and thyroid hormones T3 & T4 (triiodothyronine & thyroxine, respectively).

Since an underactive thyroid causes the pituitary gland – located in the brain – to release more TSH, clinical endocrinologists will commonly measure TSH levels as an initial thyroid screening test. However, T3 and T4 are the hormones the thyroid gland produces, acting as direct indicators of thyroid functioning.

A high TSH level, along with a low level of free T3 and T4 (the active hormones not bound to proteins), suggest an underactive thyroid gland.

How do you treat an Underactive Thyroid?

The primary treatment for an underactive thyroid is hormone replacement therapy, typically with the synthetic thyroid hormone thyroxine (levothyroxine). This medication restores low thyroid levels to their normal range, which you can monitor by looking out for signs your thyroid medication is working. The dosage of thyroxine is adjusted based on individual needs, determined through a regular blood test measuring thyroid hormone levels[4]. It's crucial to ensure that your thyroid medication is not too low, especially in the case of subclinical hypothyroidism, where TSH is elevated but T3 and T4 levels are normal, careful monitoring may be recommended instead of immediate treatment.

Treatment may also involve addressing related health issues such as elevated cholesterol or heart disease, often associated with hypothyroidism. Additionally, lifestyle changes – including a balanced diet and regular exercise – can be beneficial in restoring thyroid levels. To gain a deeper understanding of your thyroid health and how to test for hypothyroidism, consider exploring Everlywell's Online Thyroid Consultation.

What Happens if an Underactive Thyroid Isn’t Treated?

Untreated hypothyroidism could cause symptoms to worsen, potentially leading to more serious issues including:

• Mental health issues, such as depression
• Impaired memory
• Slowed heart rate, potentially leading to heart failure
• Infertility
• Severe muscle weakness and pain

Life-threatening conditions, such as a myxedema coma or peripheral neuropathy, can arise from severe hypothyroidism [5]. It's important to take a blood test and consult with a provider to regulate your thyroid hormone level. Checking your thyroid levels at home can be a crucial first step if you exhibit underactive thyroid symptoms.

Detect an Underactive Thyroid at Home with Everlywell Hormone Testing

Everlywell currently offers a comprehensive Thyroid Test that measures TSH, T3 & T4 levels, and thyroid peroxidase antibodies (TPO). This blood test not only examines hypothyroidism but also helps identify hyperthyroidism (AKA, an overactive thyroid).

In addition to our Thyroid Test, Everlywell also offers Heavy Metal Testing for minerals that can affect the thyroid, including Iodine, Selenium, and Bromine. Furthermore, if hypothyroidism is suspected, the Everlywell Heart Health Test can assess whether cholesterol or blood sugar is elevated, and if this could be corrected by addressing the Thyroid issue.

By understanding thyroid function and hypothyroidism symptoms, you can manage your weight, energy levels, and risk of complications for your general health and overall well-being.

What are the potential early signs of thyroid problems?

Hypothyroidism vs. hyperthyroidism: the key differences explained

23 possible symptoms of an overactive thyroid

1. Hypothyroidism: an underestimated issue. American Thyroid Association. URL. Accessed Dec 23, 2023.
2. How medications affect thyroid function. Medicine Cabinet. URL. Accessed Dec 23, 2023.
3. Lifestyle is associated with thyroid function in subclinical hypothyroidism: a cross-sectional study. BMC Endocrine Disorders. URL. Accessed Dec 23, 2023.
4. Levothyroxine. NHS. URL. Accessed Dec 23, 2023.
5. Clinical Manifestations of Severe Untreated Hypothyroidism. Cureus. URL. Accessed Dec 23, 2023.