The thyroid is a butterfly-shaped gland located at the base of your neck, in front of the windpipe. Although there are many glands in our bodies, the thyroid is especially important because it produces hormones that control metabolic processes throughout our bodies.
These metabolic processes depend on the thyroid sending out its hormones in just the right amounts. Too little or too much, and things begin to go awry. In this article, we explore the science behind the thyroid condition hypothyroidism (low thyroid), its causes and treatments, and how it differs from hyperthyroidism (high thyroid).
What Is the Thyroid Gland?
The thyroid is an endocrine gland, meaning it produces hormones that travel to, and have influence on, other parts of the body. Hormones are incredible molecules with the ability to communicate across our bodies. There are hormones that regulate our growth, stimulate development of our reproductive organs, and even control what happens when we feel stressed. (Source)
The Thyroid Hormones
The thyroid’s two primary hormones, triiodothyronine (T3) and thyroxine (T4), regulate metabolism — the complex chemical reactions that power all the work our bodies do. (Source)
The thyroid gland produces a third hormone, calcitonin, that reduces the amount of calcium in the blood if it gets too high. Although this is important for maintaining your body’s homeostasis, or equilibrium, calcitonin isn’t one of the hormones that concern us when we talk about hypo- and hyperthyroidism. (Source)
Hypothyroidism vs. Hyperthyroidism
As with many hormones, it is important that the concentration of thyroid hormones in your body stays within a certain range. When your thyroid gland does not produce the right amount of hormones, you may develop a thyroid condition. Hypothyroidism and hyperthyroidism are two thyroid conditions whose names sound very similar and are often confused.
Hypothyroidism is a condition in which your thyroid gland is underactive and is not producing enough thyroid hormones. On the other hand, hyperthyroidism is a condition in which your thyroid gland is overactive and is producing excess amounts of thyroid hormones.
Hypothyroidism is the more common of the two thyroid conditions, affecting around 3%–7% of the U.S. population. Hyperthyroidism, on the other hand, only affects around 1%–3% of people in the U.S. (Source, Source)
Either of these thyroid conditions can have symptoms and effects that range from mild to severe, depending on how underactive or overactive the thyroid gland is. The symptoms and treatments for hypothyroidism and hyperthyroidism can vary greatly, but either can go undiagnosed for a long time. (Source, Source)
Symptoms of Hypothyroidism
The symptoms of an underactive thyroid gland vary from person to person and depend on factors such as age and sex, with older people tending to have less obvious symptoms than younger people.
Common symptoms of hypothyroidism include:
- dry skin
- cold sensitivity or intolerance
- weight gain
- voice change
- muscle cramping
- sleep apnea*
- carpal tunnel syndrome*
* may be present in severe cases of hypothyroidism (Source)
Symptoms of Hyperthyroidism
As with hypothyroidism, the symptoms of hyperthyroidism depend on the individual’s age, sex, and underlying health conditions. Common symptoms include:
- weight loss
- goiter (enlarged thyroid gland)
- increased sweating
- extreme thirst
- elevated, strong, or irregular heartbeat
- poor concentration
- tremors in extremities
Causes of Hypothyroidism vs. Hyperthyroidism
The two thyroid disorders also have different causes, although both may result from autoimmune processes.
Causes of Hypothyroidism
The most common cause of hypothyroidism is Hashimoto’s thyroiditis, or Hashimoto’s disease. This is an autoimmune disorder in which the immune system attacks the thyroid gland, gradually destroying it. Hashimoto’s disease causes the thyroid gland to become inflamed and unable to produce sufficient thyroid hormones. (Source)
Another cause of hypothyroidism is the use of lithium. Often taken as a medication, lithium can affect the synthesis and secretion of thyroid hormones. Severe iodine deficiency can also lead to hypothyroidism because iodine is needed to synthesize thyroid hormones. (Source, Source)
Causes of Hyperthyroidism
Hyperthyroidism, on the other hand, is most commonly caused by Graves’ disease, another autoimmune condition. Normally, a hormone called thyroid stimulating hormone (TSH), released by the pituitary gland, binds to receptors on the thyroid and stimulates it to produce its thyroid hormones.
Graves’ is thought to result when autoantibodies bind to those receptors, causing the thyroid to overproduce its hormones. Like other autoimmune disorders, Graves’ is more common in women than in men.
Other causes of hyperthyroidism include solitary toxic adenomas, which are lumps that grow on the thyroid and produce thyroid hormones. Once common in iodine-deficient areas, there may be a genetic component to development of thyroid adenomas. On the other hand, iodine-induced thyroid dysfunction may be caused by ingesting excessive amounts of iodine. (Source, Source)
Treatment of Hypothyroidism vs. Hyperthyroidism
Thyroid hormone replacement therapy is commonly used to treat hypothyroidism.
The drug levothyroxine can be taken as a thyroid hormone replacement therapy. Levothyroxine works by supplementing thyroid hormones in your body so your thyroid hormone levels are normal. The dosage of levothyroxine depends on age and health conditions. For example, women may need to increase their levothyroxine dose by 30% when they become pregnant because of changes that occur in their bodies during pregnancy. (Source, Source)
There are three types of treatment for individuals seeking to manage or cure their hyperthyroidism.
- Antithyroid Drugs (ATDs)
Propylthiouracil, carbimazole, and thiamazole are examples of ATDs that can be taken to treat hyperthyroidism. These drugs work by targeting the thyroid gland and inhibiting thyroid hormone production. About 5% of patients experience minor side effects such as joint pain and gastrointestinal problems, and there is a high relapse rate if treatment is stopped.
A thyroidectomy can be performed to remove the thyroid gland and cure hyperthyroidism. This is the most successful treatment in individuals who have Graves’ disease, and surgical side-effects are rare. However, after surgery, the individual will no longer produce thyroid hormones and will need to start thyroid replacement therapy. (Source)
- Radioactive Iodine Therapy
Radioactive iodine therapy is a type of radiation therapy used to destroy enough thyroid tissue so the patient is no longer producing excess thyroid hormones. This treatment type is recommended for patients who are not good candidates for surgery. Radioactive iodine therapy is generally safe and effective, although side effects do occur. Lifelong thyroid level monitoring is needed due to the possibility of permanent hypothyroidism. (Source, Source)
Normal Thyroid Hormone Levels
“Normal” T4, T3, and TSH levels can vary based on age, the testing facility, and other factors such as pregnancy.
Free Thyroxine (T4)
- Normal range, free T4: 0.7 ng/dL to 1.9 ng/dL
Thyroxine, or T4, makes up about 95% of the thyroid hormones circulating in the blood. Most T4 is bound to proteins and unavailable for immediate use; this creates a pool of T4 that can be drawn from as needed. In lab tests, the protein-bound T4 is known as bound T4, whereas T4 that is not protein-bound is known as free T4, and together they make up total T4. However, free T4 tests are generally used to assess thyroid function. Several medications and medical conditions can affect T4 levels. (Source)
- Normal range, total T3: 80 ng/dL to 220 ng/dL
Triiodothyronine, or T3, is the active thyroid hormone that actually enters cells and affects their function. T3 is formed by removing an iodine atom from T4. Like T4, T3 is found in both bound and free forms. Free T3 tests can support a hyperthyroidism diagnosis. By the time T3 levels start falling hypothyroidism is usually pretty far advanced, so they aren’t very helpful in diagnosing thyroid dysfunction. (Source)
Thyroid-Stimulating Hormone (TSH, thyrotropin)
- Normal range: 0.35 mlU/mL to 4.50 mlU/mL
A high TSH may indicate an underactive thyroid (hypothyroidism), while a low TSH may indicate an overactive thyroid (hyperthyroidism). An abnormal TSH level with normal T3 and T4 levels may indicate a subclinical thyroid dysfunction — one that has not yet caused symptoms. (Source)
It may seem counterintuitive that TSH is elevated when the thyroid is underperforming, but this happens because the pituitary gland is registering low thyroid hormone output and trying to stimulate the thyroid to increase production. On the other hand, when the pituitary senses high thyroid hormone levels, it will decrease the amount of TSH it sends out, trying to lower thyroid hormone production to normal levels. (Source)
One Other Thyroid Test: Thyroid Antibodies
Another test that helps uncover thyroid disease is a thyroid antibodies test. Antibodies are proteins that your body produces to fight a virus or bacteria. However, when you have an autoimmune condition, antibodies mistake your body’s normal cells for foreign tissue and attack the cells. Hashimoto’s thyroiditis and Graves’ disease are both autoimmune diseases, and antithyroid antibodies may be detectable long before thyroid hormone levels become abnormal. (Source)
Hypothyroidism in Men
Hypothyroidism is five to 10 times more common in women than in men. One explanation for this difference might be that autoimmune diseases in general occur twice as often in women than in men. Despite this difference, the symptoms of hypothyroidism in men are nearly the same as those in women. (Source, Source)
In addition to the common hypothyroidism symptoms listed above, however, men with hypothyroidism may also experience:
- lowered sperm count
- abnormally shaped sperm
- lowered sperm motility (swimming ability)
- erectile dysfunction (ED)
- hypoactive sexual desire
- gynecomastia (enlarged breast tissue)
Hypothyroidism and Pregnancy
In pregnant women, it’s important to consider two types of hypothyroidism, because each type can have a different effect on the pregnancy.
- Subclinical Hypothyroidism
Subclinical hypothyroidism is defined as having an abnormal TSH level but normal T3 and T4 levels. This type is considered the less advanced form of hypothyroidism. Although there is evidence that subclinical hypothyroidism in the mother can lead to adverse pregnancy outcomes, there is also contradicting evidence, and more research must be done to confirm a causal relationship.
- Overt Hypothyroidism
Overt hypothyroidism is the more advanced of the two and is defined as having both abnormal TSH and abnormal thyroid hormone levels. If untreated, overt hypothyroidism can cause complications in pregnant women such as preterm birth, preeclampsia, and miscarriage. There is also evidence that overt hypothyroidism can affect neurological and psychological development in the baby. However, you can lower your risk of developing these birth complications by taking a thyroid hormone replacement medication if needed. (Source, Source)
Hashimoto’s disease remains the most common cause of hypothyroidism in pregnant women. In general, if you are pregnant and receive a hypothyroidism diagnosis, it is important to consult your health care provider and monitor your TSH levels to minimize your risk of birth complications.
Is Hypothyroidism Genetic?
The short answer is maybe. Evidence suggests there’s a good chance that you and your parents have fairly similar thyroid hormone levels and similar likelihoods of developing a thyroid disorder. However, there is no evidence of a single gene that causes thyroid disorders. Autoimmune thyroid disorders are commonly present in multiple family members, but we do not have evidence that hypothyroidism is genetic. (Source)
What to Eat: Hypothyroidism Diet Plan
Although there is no science-backed hypothyroidism diet, there are a few key micronutrients that may improve thyroid health and help treat symptoms of hypothyroidism. (Source)
Consume foods high in iodine, such as grains and seafood, because iodine is needed to make thyroid hormones. However, there is no strong evidence that iodine-rich foods can reverse hypothyroidism symptoms.
Iron plays an important role in the synthesis of thyroid hormones, and iron deficiency has been linked to decreased metabolism of T3 and T4. However, there is a lack of evidence that iron supplements or micronutrient supplements in general will affect the concentrations of T3 and T4.
Zinc is essential for maintaining thyroid function and converting thyroid hormones such as T4 to an active form where this hormone can be used in the body. Like iron, zinc is important in the metabolism of thyroid hormones, but more research must be conducted to understand how these micronutrients affect thyroid hormone levels.
Selenium is a micronutrient that has a protective antioxidant effect on the thyroid gland and is needed for production of thyroid hormones. Excessive intake of selenium through unregulated supplements can be toxic, so instead try incorporating selenium-rich foods, such as Brazil nuts and tuna, into your diet. (Source, Source)
Follow an AIP Diet
Following a gluten-free diet or paleo, autoimmune protocol (AIP) can reduce inflammation in the gut and help individuals identify foods that cause an immune response. The AIP diet begins by eliminating inflammatory foods and then reintroducing these foods to allow the individual to identify food groups that cause their symptoms. A 2019 study found these diets can reduce inflammation and regulate immune function in individuals with Hashimoto’s disease. However, there is no evidence that these diets improve thyroid function in people with Hashimoto’s. (Source, Source)
Should You Avoid Goitrogens?
Certain foods contain compounds called goitrogens, which may interfere with thyroid hormone production. Goitrogens are inactivated by cooking and the research suggests that, even raw, these foods are not likely to be a problem if you’re getting enough iodine in your diet.
Foods that contain goitrogens include:
- cruciferous vegetables
- bok choy
- white and red cabbage
- Brussels sprouts
- soy products
Can Hypothyroidism Be Cured Permanently?
Currently, there is no scientific evidence that supports the curability of hypothyroidism. Like other autoimmune diseases, hypothyroidism is most likely manageable but not necessarily “curable.” Treatment simply maintains your thyroid hormone levels at a normal level, but no evidence exists to suggest treatment changes the level of thyroid antibodies that your body produces. (Source)