Hypothyroidism: Symptoms, Causes & Treatment

What Is Hypothyroidism?

Hypothyroidism is a condition where the thyroid gland doesn't produce enough thyroid hormones (T4 and T3), which regulate metabolism. This causes the body's functions to slow down, leading to symptoms like fatigue, weight gain, and cold intolerance. It affects approximately 4-5% of adults and is more common in women and older individuals.

The thyroid gland is a butterfly-shaped organ located in the front of your neck, just below your Adam's apple. Despite its small size, the thyroid plays a crucial role in regulating virtually every cell in your body through the hormones it produces. When the thyroid becomes underactive, it produces less of these essential hormones than your body needs, resulting in a widespread slowdown of bodily functions.

Thyroid hormones primarily control your metabolism - the process by which your body converts food into energy. When thyroid hormone levels drop, your metabolism slows, affecting everything from how quickly you burn calories to how fast your heart beats. This explains why hypothyroidism can cause such a wide range of symptoms affecting multiple organ systems throughout the body.

The condition can develop at any age but becomes increasingly common as you get older. Women are significantly more likely to develop hypothyroidism than men, with estimates suggesting they are 5-8 times more at risk. While hypothyroidism is typically a lifelong condition requiring daily medication, the excellent news is that treatment is highly effective. Most people with properly managed hypothyroidism live completely normal lives with no limitations on their activities.

The thyroid's role in your body

Your thyroid produces two main hormones: thyroxine (T4) and triiodothyronine (T3). T4 is the primary hormone produced and serves as a reservoir that is converted to the more active T3 form in tissues throughout your body. These hormones influence nearly every organ system, including your brain, heart, muscles, skin, and digestive tract.

The thyroid is controlled by the pituitary gland, a pea-sized structure at the base of your brain. The pituitary produces thyroid-stimulating hormone (TSH), which signals the thyroid to produce more or less hormone. When thyroid hormone levels are low, TSH rises in an attempt to stimulate more production - this is why a high TSH level is the hallmark sign of hypothyroidism on blood tests.

What Are the Symptoms of Hypothyroidism?

The most common symptoms of hypothyroidism include persistent fatigue, unexplained weight gain, feeling cold when others are comfortable, constipation, dry skin and hair, depression, and difficulty concentrating. Symptoms typically develop gradually over months and may initially be attributed to aging or stress.

One of the challenging aspects of hypothyroidism is that symptoms often develop so gradually that they may go unnoticed for months or even years. Many people adapt to feeling increasingly tired or slightly off without realizing there's an underlying medical cause. Additionally, because thyroid hormones affect so many body systems, the symptoms of hypothyroidism can be remarkably varied and may initially seem unrelated to each other.

The symptoms you experience depend on how low your thyroid hormone levels are and how quickly they've dropped. Some people with mildly low levels may have minimal symptoms, while others with more significant deficiencies experience more pronounced effects. It's also common to experience only some symptoms while not having others - there's no single "typical" presentation of hypothyroidism.

Early warning signs

In the earliest stages of hypothyroidism, you might notice subtle changes that are easy to dismiss. The most common early symptoms include:

• Fatigue and low energy: Feeling tired even after adequate sleep, needing more rest than usual, or finding your energy depletes faster during the day
• Feeling cold: Becoming unusually sensitive to cold temperatures or needing extra layers when others feel comfortable
• Concentration difficulties: Experiencing "brain fog," struggling to focus, or feeling mentally sluggish
• Mild depression or low mood: Feeling unexplainably sad, losing interest in activities you normally enjoy
• Slight weight gain: Gaining weight despite no changes to diet or exercise habits

Symptoms that develop over time

As hypothyroidism progresses without treatment, additional symptoms typically emerge and existing symptoms may worsen. Over weeks to months, you may also experience:

• Dry, rough skin: Your skin may become noticeably dry, flaky, or rough to the touch
• Hair loss and brittleness: Hair may become thin, brittle, and fall out more easily; eyebrows may thin (especially the outer third)
• Constipation: Slowed metabolism affects the digestive system, leading to less frequent bowel movements
• Muscle aches and weakness: Generalized muscle pain, stiffness, or weakness
• Joint pain: Aching or stiffness in joints, particularly in the hands and feet
• Slow heart rate (bradycardia): Heart rate may drop below 60 beats per minute
• Puffy face: Facial puffiness, particularly around the eyes, due to fluid accumulation
• Menstrual irregularities: Heavier, more frequent, or more painful periods in women
• Decreased libido: Reduced interest in sexual activity
• Memory problems: Difficulty remembering things or feeling mentally "foggy"

When symptoms indicate a thyroid problem

A key distinguishing feature of hypothyroidism symptoms is that multiple symptoms typically occur together. While any single symptom might have many causes, experiencing several symptoms simultaneously - especially fatigue combined with cold intolerance, weight gain, and constipation - strongly suggests a thyroid problem and warrants testing.

What Causes Hypothyroidism?

The most common cause of hypothyroidism is Hashimoto's thyroiditis, an autoimmune condition where the immune system attacks the thyroid gland. Other causes include thyroid surgery, radiation treatment, certain medications, iodine deficiency, pituitary disorders, and congenital thyroid problems.

Understanding what causes hypothyroidism helps explain why some people develop the condition and others don't. While several factors can lead to an underactive thyroid, they all ultimately result in the thyroid gland being unable to produce sufficient hormones to meet the body's needs.

Hashimoto's thyroiditis (autoimmune thyroiditis)

The most common cause of hypothyroidism in areas with adequate iodine intake is Hashimoto's thyroiditis, named after the Japanese doctor who first described it in 1912. This is an autoimmune condition in which the immune system mistakenly produces antibodies that attack the thyroid gland, gradually destroying its ability to produce hormones.

In Hashimoto's disease, the immune system treats thyroid tissue as foreign and targets it for destruction. Over time, this ongoing attack damages enough thyroid cells that the gland can no longer produce adequate hormones. The progression is usually slow, often taking years before symptoms become noticeable. The thyroid may become enlarged (goiter) as it tries to compensate for decreased function, or it may shrink due to the autoimmune destruction.

The exact reason why the immune system attacks the thyroid isn't fully understood, but both genetic and environmental factors appear to play roles. Hashimoto's disease tends to run in families and is associated with other autoimmune conditions such as type 1 diabetes, celiac disease, and rheumatoid arthritis.

Treatment-related causes

Some cases of hypothyroidism occur as a result of medical treatments for other conditions:

• Thyroid surgery: Removal of part or all of the thyroid gland (thyroidectomy) for conditions like thyroid cancer, nodules, or hyperthyroidism will reduce or eliminate hormone production
• Radioactive iodine treatment: Used to treat hyperthyroidism or thyroid cancer, radioactive iodine destroys thyroid tissue and frequently leads to hypothyroidism
• Radiation therapy: External radiation to the head or neck area for cancers can damage the thyroid gland

Medications that affect thyroid function

Several medications can interfere with thyroid hormone production:

• Lithium: Used for bipolar disorder, lithium can inhibit thyroid hormone release
• Amiodarone: This heart medication contains iodine and can cause either hypothyroidism or hyperthyroidism
• Interferon-alpha: Used for hepatitis C and some cancers, can trigger autoimmune thyroid problems
• Certain cancer immunotherapies: Checkpoint inhibitors used in cancer treatment can cause thyroid dysfunction

Other causes

Less common causes of hypothyroidism include:

• Iodine deficiency: The thyroid needs iodine to produce hormones. In areas without iodized salt, iodine deficiency remains a leading cause of hypothyroidism worldwide
• Pregnancy and postpartum: Some women develop thyroid problems during or after pregnancy that may resolve or become permanent
• Pituitary disorders: Rarely, problems with the pituitary gland affect TSH production and secondarily cause hypothyroidism
• Congenital hypothyroidism: Some babies are born without a functioning thyroid gland or with a gland that doesn't produce enough hormone

Risk factors for developing hypothyroidism

Certain factors increase your likelihood of developing hypothyroidism:

• Being female: Women are 5-8 times more likely to develop hypothyroidism
• Age over 60: Risk increases significantly with age
• Family history: Having relatives with thyroid disease increases your risk
• Other autoimmune conditions: Conditions like type 1 diabetes, rheumatoid arthritis, or celiac disease are associated with higher risk
• Previous thyroid problems: History of thyroid surgery, radiation, or temporary thyroiditis

How Is Hypothyroidism Diagnosed?

Hypothyroidism is diagnosed through blood tests that measure TSH (thyroid-stimulating hormone) and free T4 levels. A high TSH level with low T4 confirms hypothyroidism. Your doctor may also test for TPO antibodies to identify autoimmune thyroiditis (Hashimoto's disease) as the underlying cause.

Diagnosing hypothyroidism is straightforward once it's suspected. The challenge often lies in recognizing when symptoms warrant testing, as many hypothyroidism symptoms are nonspecific and can be attributed to other causes. If you're experiencing symptoms consistent with hypothyroidism, or if you have risk factors for the condition, your doctor can confirm or rule out the diagnosis with simple blood tests.

Physical examination

During your appointment, your doctor will typically ask about your symptoms, their duration, and any family history of thyroid disease. The physical examination may include:

• Checking your neck for thyroid enlargement (goiter) or nodules
• Measuring your heart rate and blood pressure
• Examining your skin, hair, and nails for typical changes
• Testing your reflexes, which may be slowed in hypothyroidism

Blood tests for thyroid function

Blood tests are the definitive way to diagnose hypothyroidism. The key tests include:

TSH (Thyroid-Stimulating Hormone): This is the primary screening test for thyroid dysfunction. In hypothyroidism, TSH levels are elevated because the pituitary gland produces more TSH to try to stimulate an underactive thyroid to produce more hormone. Normal TSH is typically between 0.4-4.0 mIU/L, though optimal ranges may vary slightly between laboratories.

Free T4 (Thyroxine): This measures the amount of unbound, active thyroid hormone in your blood. In hypothyroidism, free T4 levels are low or at the lower end of normal. Testing free T4 along with TSH helps distinguish between primary hypothyroidism (thyroid gland problem) and secondary hypothyroidism (pituitary problem).

TPO Antibodies (Thyroid Peroxidase Antibodies): These antibodies indicate autoimmune thyroiditis (Hashimoto's disease). While not always necessary for treatment, knowing whether hypothyroidism is autoimmune helps predict its course and may affect other health considerations.

Understanding your test results

Interpreting thyroid test results requires understanding the relationship between TSH and thyroid hormones:

• High TSH, low T4: Confirms primary hypothyroidism - the thyroid gland isn't producing enough hormone
• High TSH, normal T4: Indicates subclinical (mild) hypothyroidism - early-stage disease that may or may not require treatment
• Normal TSH, low T4: May suggest secondary hypothyroidism (pituitary problem) - rare but requires additional evaluation

When to get tested

Consider thyroid testing if you have symptoms of hypothyroidism, especially if you also have risk factors like being female, over age 60, or having a family history of thyroid disease. Routine screening is recommended for:

• Women over age 60
• Women who are pregnant or planning pregnancy
• People with other autoimmune conditions
• Those with a family history of thyroid disease
• Anyone who has had thyroid surgery or radiation treatment

How Is Hypothyroidism Treated?

Hypothyroidism is treated with daily thyroid hormone replacement medication, typically levothyroxine (synthetic T4). Treatment is highly effective - most people notice improvement within 2-4 weeks. The dose is individualized based on blood tests and adjusted until TSH levels normalize. Most people require lifelong treatment.

The treatment for hypothyroidism is remarkably straightforward and effective: replacing the hormone your thyroid isn't making in sufficient quantities. With proper treatment, virtually all people with hypothyroidism can achieve normal thyroid levels and live without symptoms or limitations.

Levothyroxine: The standard treatment

Levothyroxine (also known as L-thyroxine, with brand names including Synthroid, Levoxyl, and Euthyrox) is the standard treatment for hypothyroidism. It's a synthetic form of the T4 hormone that is identical to what your thyroid would naturally produce. Once absorbed, your body converts it to the active T3 hormone as needed.

Levothyroxine comes as a tablet taken once daily, typically in the morning on an empty stomach. The medication is absorbed best when taken consistently at the same time each day, and certain foods and medications can interfere with absorption if taken too close together.

Starting treatment and dose adjustment

Your doctor will typically start you on a low dose of levothyroxine and gradually increase it. This approach is safer, particularly for older patients or those with heart disease, as sudden increases in thyroid hormone can stress the cardiovascular system.

Finding the right dose takes time and patience. After starting treatment or any dose change, you'll need blood tests (usually after 6-8 weeks) to check your TSH level. Based on these results, your dose may be increased, decreased, or maintained. This process may take several months until your dose is optimized.

When to expect improvement

Most people begin noticing improvements within 2-4 weeks of starting levothyroxine:

• Energy levels: Often the first symptom to improve, many people feel less fatigued within the first few weeks
• Mental clarity: Brain fog and concentration difficulties typically improve within weeks
• Mood: Depression and low mood often lift as thyroid levels normalize
• Physical symptoms: Changes to skin, hair, and weight may take longer - sometimes several months - to fully resolve

How to take levothyroxine correctly

For optimal absorption and effectiveness:

• Take on an empty stomach, ideally first thing in the morning
• Wait at least 30-60 minutes before eating breakfast
• Take with water only - avoid coffee, tea, milk, or juice
• Take calcium supplements, iron supplements, and antacids at least 4 hours apart
• Be consistent with timing - take at the same time each day
• Don't stop taking your medication without consulting your doctor

Ongoing monitoring

Even after your dose is stabilized, you'll need regular monitoring. Most doctors recommend checking TSH levels:

• Every 6-8 weeks when starting treatment or after dose changes
• Every 6-12 months once your dose is stable
• If you develop new symptoms suggesting your dose needs adjustment
• During pregnancy (when hormone needs increase significantly)

Dose adjustments over time

Your levothyroxine dose may need to change over the years due to:

• Aging: Thyroid hormone needs may decrease slightly with age
• Weight changes: Significant weight gain or loss affects dosing
• Pregnancy: Hormone requirements increase substantially during pregnancy
• Other medications: Starting or stopping certain drugs can affect thyroid hormone absorption or metabolism
• Disease progression: In Hashimoto's, continued thyroid damage may require dose increases over time

What Are the Complications of Untreated Hypothyroidism?

Untreated hypothyroidism can lead to serious complications including high cholesterol and heart disease, infertility and pregnancy complications, goiter, peripheral neuropathy, and in severe cases, a life-threatening condition called myxedema coma. Early diagnosis and proper treatment prevent these complications.

While hypothyroidism is highly treatable, leaving it undiagnosed or untreated can lead to significant health problems over time. These complications underscore the importance of recognizing symptoms, getting tested, and maintaining consistent treatment.

Cardiovascular effects

Untreated hypothyroidism has significant effects on heart health. Low thyroid hormone levels cause elevated LDL ("bad") cholesterol, which increases the risk of atherosclerosis and heart disease. The heart itself works less efficiently, and over time, this can contribute to heart failure. Additionally, the fluid retention associated with hypothyroidism can lead to pericardial effusion (fluid around the heart).

Mental health and cognitive effects

The brain is highly dependent on thyroid hormones for normal function. Prolonged hypothyroidism can cause or worsen depression, and some studies suggest links to cognitive decline. Severe, long-standing hypothyroidism can cause significant memory problems and slowed thinking that may be mistaken for dementia in older adults.

Reproductive complications

Hypothyroidism can significantly affect fertility and pregnancy. In women, untreated hypothyroidism can disrupt ovulation and menstrual cycles, making conception difficult. During pregnancy, inadequate thyroid hormone can increase risks of miscarriage, preeclampsia, premature birth, and developmental problems in the baby. Proper thyroid hormone levels are critical during pregnancy, as the baby depends on maternal thyroid hormone during early development.

Myxedema coma

The most severe complication of hypothyroidism is myxedema coma, a rare but life-threatening emergency. This occurs when extremely low thyroid hormone levels cause the body to begin shutting down. Symptoms include severe cold intolerance, extreme fatigue, confusion, slowed heart rate, low blood pressure, and ultimately loss of consciousness.

Myxedema coma typically occurs in people with longstanding, severe, untreated hypothyroidism, often triggered by a stressor such as infection, cold exposure, or surgery. It requires immediate emergency treatment with intravenous thyroid hormone and supportive care. Fortunately, this complication is very rare when hypothyroidism is properly diagnosed and treated.

How Does Hypothyroidism Affect Pregnancy?

Thyroid hormone needs increase by 25-50% during pregnancy. Women with hypothyroidism should have their dose increased early in pregnancy and be monitored closely. Untreated hypothyroidism during pregnancy can increase risks of miscarriage, preterm birth, and developmental issues in the baby. With proper treatment, women with hypothyroidism can have healthy pregnancies.

Pregnancy places significant demands on the thyroid gland. Even women with normal thyroid function produce more thyroid hormone during pregnancy to support both their own increased metabolism and the developing baby. For women with hypothyroidism, this means that medication doses almost always need to increase during pregnancy.

Before becoming pregnant

If you have hypothyroidism and are planning pregnancy, it's important to:

• Ensure your thyroid levels are well-controlled before conception
• Discuss your plans with your doctor so they can optimize your medication
• Aim for a TSH level in the lower half of the normal range before pregnancy

During pregnancy

Once pregnant, thyroid hormone requirements increase significantly - typically by 25-50%. Many endocrinologists recommend increasing the levothyroxine dose by 25-30% as soon as pregnancy is confirmed, then adjusting based on blood tests. More frequent monitoring is essential during pregnancy:

• TSH should be checked every 4-6 weeks during the first half of pregnancy
• The goal is to maintain TSH in the trimester-specific reference range (generally lower than non-pregnant ranges)
• Continue monitoring in the second half of pregnancy, though adjustments are usually less frequent

Importance of adequate iodine

Iodine requirements increase during pregnancy and breastfeeding because the baby needs iodine for thyroid development. Most prenatal vitamins contain iodine, but women with hypothyroidism should ensure they're getting adequate amounts. Discuss iodine supplementation with your healthcare provider.

After delivery

After giving birth, thyroid hormone requirements typically return to pre-pregnancy levels. Your doctor will usually reduce your levothyroxine dose back to your pre-pregnancy amount shortly after delivery and recheck your TSH level after 6-8 weeks to confirm appropriate dosing.

Can Hypothyroidism Be Prevented?

Most cases of hypothyroidism, especially those caused by Hashimoto's disease, cannot be prevented. However, ensuring adequate iodine intake (through iodized salt, dairy, and seafood) can prevent iodine-deficiency hypothyroidism. Early detection through screening in high-risk groups allows prompt treatment before complications develop.

Since the most common cause of hypothyroidism is autoimmune (Hashimoto's disease), and the triggers for autoimmune conditions are not fully understood, there's no proven way to prevent most cases of hypothyroidism. However, there are steps you can take to reduce risk and ensure early detection.

Adequate iodine intake

Your thyroid needs iodine to produce hormones. In areas where iodized salt is not commonly used, iodine deficiency remains a significant cause of hypothyroidism. To ensure adequate iodine intake:

• Use iodized salt rather than regular table salt or specialty salts
• Include iodine-rich foods: dairy products, seafood, eggs
• If you follow a restrictive diet (vegan, no dairy), consider an iodine supplement
• Pregnant and breastfeeding women need extra iodine - most prenatal vitamins contain it

Know your risk factors

Being aware of risk factors helps you and your doctor know when to screen for thyroid problems:

• Family history of thyroid disease
• Personal history of other autoimmune conditions
• Previous thyroid surgery or radiation
• Being female, especially over age 60
• Recent pregnancy

Early detection

While you can't prevent most hypothyroidism, early detection through screening allows treatment before symptoms become severe or complications develop. If you have risk factors or notice symptoms, don't hesitate to ask your doctor about thyroid testing.