Hypothyroidism

Overview

Hypothyroidism is a condition in which the thyroid gland does not produce enough thyroid hormones to meet the body’s needs. Thyroid hormones—primarily thyroxine (T4) and triiodothyronine (T3)—play a critical role in regulating metabolism, energy production, temperature control, heart function, and brain health.

Hypothyroidism is commonly identified through an elevated Thyroid-Stimulating Hormone (TSH) level on blood testing and is one of the most frequent endocrine disorders worldwide.

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What the Thyroid Does

The thyroid is a small, butterfly-shaped gland located at the front of the neck. It produces hormones that influence nearly every organ system, including:

• Metabolic rate and energy expenditure

• Body temperature regulation

• Heart rate and cardiovascular function

• Digestion and gut motility

• Brain function and mood

• Growth, fertility, and pregnancy health

When thyroid hormone levels are too low, many of these systems slow down.

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Causes of Hypothyroidism

Hypothyroidism can develop for several reasons. The most common causes include:

Autoimmune Thyroid Disease

• Hashimoto’s thyroiditis is the leading cause in iodine-sufficient countries

• The immune system attacks thyroid tissue, gradually reducing hormone production

Iodine Deficiency

• Still a major cause globally

• Iodine is required to produce thyroid hormones

Thyroid Surgery or Radioactive Iodine

• Removal or destruction of thyroid tissue for hyperthyroidism or cancer

Medications

• Lithium, amiodarone, and some immune therapies

Congenital or Genetic Causes

• Present at birth, though less common

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Symptoms of Hypothyroidism

Symptoms often develop gradually and may be subtle at first. They can vary based on age, severity, and duration.

Common symptoms include:

• Fatigue and low energy

• Weight gain or difficulty losing weight

• Cold intolerance

• Dry skin and hair loss

• Constipation

• Brain fog, poor concentration, or memory issues

• Depression or low mood

• Muscle weakness or cramps

• Menstrual irregularities and fertility issues

In more severe cases, untreated hypothyroidism can lead to anemia, heart problems, and nerve dysfunction.

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Hypothyroidism and TSH

TSH (Thyroid-Stimulating Hormone) is produced by the pituitary gland and signals the thyroid to make hormones.

• In primary hypothyroidism, the thyroid underperforms

• The pituitary responds by increasing TSH to stimulate the thyroid

• As a result, TSH is typically elevated, while free T4 is low or low-normal

This makes TSH the most sensitive initial marker for detecting hypothyroidism.

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How Hypothyroidism Is Diagnosed

Diagnosis is based on blood testing and clinical context.

Common tests include:

• TSH (Thyroid-Stimulating Hormone)

• Free T4

• Free T3 (in selected cases)

• Thyroid antibodies (TPO and thyroglobulin antibodies) to assess for autoimmune disease

Typical Lab Patterns

• Overt hypothyroidism: High TSH + low free T4

• Subclinical hypothyroidism: High TSH + normal free T4

Tracking these markers together provides a more complete picture than TSH alone.

Platforms like HealthMatters.io allow you to upload, track, and visualize TSH and related thyroid markers over time, making it easier to understand trends rather than isolated results.

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Subclinical Hypothyroidism

Subclinical hypothyroidism occurs when TSH is elevated but free T4 remains within the reference range.

• Often asymptomatic or mildly symptomatic

• May progress to overt hypothyroidism, especially in autoimmune disease

• Management depends on TSH level, symptoms, age, pregnancy status, and antibody presence

This is a common source of confusion and an important reason for longitudinal lab tracking.

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Treatment of Hypothyroidism

Treatment aims to restore normal thyroid hormone levels and relieve symptoms.

Thyroid Hormone Replacement

• Levothyroxine (synthetic T4) is the standard treatment

• Dose is individualized based on TSH, body weight, age, and comorbidities

• Blood levels are typically rechecked after 6–8 weeks when adjusting therapy

Some patients may also be evaluated for combination T4/T3 therapy under specialist care.

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Nutrients That Support Thyroid Function

Several nutrients are important for thyroid hormone production and metabolism:

• Iodine: Required to make thyroid hormones

• Selenium: Supports hormone conversion and antioxidant protection

• Iron: Necessary for thyroid enzyme function

• Zinc: Involved in hormone signaling

Deficiencies in these nutrients may worsen thyroid dysfunction in susceptible individuals.

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When to Seek Medical Evaluation

You should consider testing or medical evaluation if you experience:

• Persistent fatigue or unexplained weight gain

• Cold intolerance or hair thinning

• Fertility challenges or menstrual changes

• A personal or family history of thyroid disease

• Abnormal TSH or thyroid hormone levels

Early detection and treatment can prevent long-term complications.

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Summary

Hypothyroidism is a common condition in which the thyroid does not produce enough hormones to support normal metabolic function. It is most often detected through an elevated TSH level and may be caused by autoimmune disease, iodine deficiency, or thyroid damage.

Because symptoms can be subtle and lab values can change over time, tracking thyroid markers—especially TSH and free T4—provides critical insight into diagnosis, treatment response, and long-term thyroid health.

FAQ: Hypothyroidism

What is hypothyroidism?

Hypothyroidism is a condition in which the thyroid gland does not produce enough thyroid hormones to meet the body’s needs. These hormones regulate metabolism, energy production, body temperature, and many other essential functions.

What are the most common symptoms of hypothyroidism?

Common symptoms include fatigue, weight gain, cold intolerance, dry skin, hair loss, constipation, brain fog, depression, muscle weakness, and menstrual irregularities. Symptoms often develop gradually and may vary in severity.

What causes hypothyroidism?

The most common cause is Hashimoto’s thyroiditis, an autoimmune condition in which the immune system attacks the thyroid. Other causes include iodine deficiency, thyroid surgery, radioactive iodine treatment, certain medications, and congenital thyroid disorders.

How is hypothyroidism diagnosed?

Hypothyroidism is diagnosed using blood tests, most commonly TSH (thyroid-stimulating hormone) and free T4. Elevated TSH with low free T4 indicates overt hypothyroidism. Thyroid antibody tests may be used to identify autoimmune causes.

What is the difference between hypothyroidism and subclinical hypothyroidism?

In overt hypothyroidism, TSH is elevated and free T4 is low. In subclinical hypothyroidism, TSH is elevated but free T4 remains within the reference range. Subclinical cases may have mild or no symptoms but can progress over time.

What TSH level indicates hypothyroidism?

TSH levels above the upper reference range—commonly above 4.0–5.0 mIU/L—may suggest hypothyroidism, depending on symptoms, free T4 levels, age, and clinical context. Interpretation should always be individualized.

How is hypothyroidism treated?

Treatment typically involves thyroid hormone replacement, most commonly levothyroxine (synthetic T4). The dose is adjusted based on TSH levels, symptoms, age, and other health factors. Regular blood testing is used to monitor response.

How long does it take to feel better after starting treatment?

Many people begin to notice improvement within a few weeks of starting treatment, but it can take 6–8 weeks or longer for thyroid hormone levels to stabilize. Symptom improvement may continue gradually over several months.

Can hypothyroidism be reversed?

In most cases, hypothyroidism—especially autoimmune hypothyroidism—is a long-term condition that requires ongoing treatment. Temporary or reversible cases may occur due to iodine deficiency, certain medications, or postpartum thyroiditis.

Does hypothyroidism cause weight gain?

Hypothyroidism can contribute to modest weight gain due to slowed metabolism and fluid retention. Treating the condition helps normalize metabolism, but weight changes are influenced by multiple factors.

Can hypothyroidism affect fertility and pregnancy?

Yes. Untreated hypothyroidism can interfere with ovulation and fertility and increase pregnancy risks. Proper diagnosis and treatment before and during pregnancy are important for both maternal and fetal health.

What other lab tests are useful in hypothyroidism?

In addition to TSH and free T4, clinicians may assess free T3, thyroid peroxidase (TPO) antibodies, thyroglobulin antibodies, iodine status, iron levels, selenium, and vitamin D to better understand thyroid function and contributing factors.