Hyperthyroidism (underactive thyroid)

What is a Thyroid Gland?

The thyroid gland is a butterfly-shaped organ located in the front of your neck, wrapped around your windpipe (trachea). Hormones are secreted to control a variety of metabolic processes, including growth and energy expenditure. The metabolism will be altered whether the thyroid gland is hyperactive or sluggish.

How does a Thyroid Gland Function?

The thyroid gland converts iodine, which is obtained through diet, into thyroid hormones such as thyroxine (T4) and triiodothyronine (T3). The only cells in the body that can absorb iodine are thyroid cells. T3 and T4 are produced when iodine and the amino acid tyrosine are combined in these cells. The thyroid hormones T3 and T4 are subsequently released into the bloodstream and carried throughout the body, where they regulate metabolism.

What Is Hypothyroidism?

Hypothyroidism is like a slowdown switch for your body. The thyroid gland, responsible for keeping your energy levels and metabolism in check, doesn’t make enough of the hormones it should. These hormones are like the gas that keeps your body’s engine running smoothly.
But when they’re in short supply, things can feel sluggish. This condition can lead to various symptoms such as fatigue, weight gain, feeling cold all the time, and even changes in mood. Managing hypothyroidism involves getting the right treatment, usually taking synthetic thyroid hormones to replace what your body isn’t making enough of.

What Are the Causes of Hypothyroidism?

Hypothyroidism occurs when the thyroid gland does not produce enough thyroid hormones to meet the body’s needs. There are several potential causes of hypothyroidism:

Autoimmune Thyroiditis (Hashimoto's Thyroiditis)

This is the most common cause of hypothyroidism in developed countries. It’s an autoimmune disorder where the body’s immune system attacks the thyroid gland, leading to inflammation and damage. Over time, the gland’s ability to produce hormones is impaired.

Thyroid Surgery or Radioactive Iodine Treatment

Surgical removal of part or all of the thyroid gland (thyroidectomy) or treatment with radioactive iodine for hyperthyroidism can sometimes result in hypothyroidism if too much thyroid tissue is removed or destroyed.

Radiation Therapy

Radiation treatment for certain cancers, especially in the neck and head area, can damage the thyroid gland and lead to hypothyroidism.

Congenital Hypothyroidism

Some babies are born with an underdeveloped or non-functioning thyroid gland, known as congenital hypothyroidism. If not detected and treated early, this condition can lead to developmental and growth issues.


Certain medications, such as lithium (used for bipolar disorder) and amiodarone (used for heart arrhythmias), can interfere with thyroid function and cause hypothyroidism.

Iodine Deficiency

The thyroid gland requires iodine to produce thyroid hormones. A lack of dietary iodine can lead to decreased hormone production and hypothyroidism. However, iodine deficiency is rare in areas where iodised salt is commonly used.

What Are Some Common Symptoms of Hypothyroidism?

The symptoms can vary widely in severity and may develop slowly over time. Common symptoms of hypothyroidism include:


Feeling unusually tired or fatigued, even after getting adequate sleep, is a common symptom.

Weight Gain

Unintentional weight gain or difficulty losing weight despite normal eating habits can occur.

Cold Sensitivity

Feeling unusually cold, particularly in the extremities, even in mild temperatures.

Dry Skin

Skin may become dry, rough, and prone to itching.

Brittle Hair and Nails

Hair might become thin, dry, and brittle, and nails can also become weak and brittle.


A slower metabolism can lead to slower digestion and constipation.

Depression and Mood Changes

Hypothyroidism can affect mood, leading to feelings of depression, anxiety, and mood swings.

Memory and Cognitive Issues

Some individuals experience problems with memory, concentration, and cognitive function.

Muscle Weakness

Muscle weakness, aches, and cramps can occur.

Joint Pain

Joint pain and stiffness can be symptoms of hypothyroidism.


Changes in the voice, such as hoarseness, can be due to the effects of hypothyroidism on the vocal cords.

Slow Heart Rate

A slower heart rate (bradycardia) can occur due to the decreased metabolic activity associated with hypothyroidism.

Irregular or Heavy Menstrual Periods

Women may experience irregular menstrual cycles or heavier-than-normal menstrual periods.

Puffy Face and Swelling

The face and extremities can appear swollen due to fluid retention.

Elevated Cholesterol Levels

Hypothyroidism can lead to an increase in cholesterol levels, contributing to cardiovascular issues.

Thinning Eyebrows

The outer third of the eyebrows may thin or become sparse.

Low Body Temperature

A consistently lower body temperature than normal is sometimes observed.

Decreased Libido

Some individuals with hypothyroidism may experience a decreased interest in sexual activity.

How Is Hypothyroidism Diagnosed?

Hypothyroidism is typically diagnosed through medical history assessment, physical examination, and laboratory tests.
  • The primary tests used to diagnose hypothyroidism measure the levels of thyroid hormones (T4 and T3) and thyroid-stimulating hormone (TSH) in the blood.

Additional Tests

  • Depending on the situation, your doctor might recommend additional tests to evaluate the thyroid function further and identify the underlying cause of hypothyroidism:
  • Thyroid Antibody Tests These tests, including anti-thyroid peroxidase antibodies (TPOAb) and anti-thyroglobulin antibodies (TgAb), can help identify autoimmune causes like Hashimoto’s thyroiditis.
  • Thyroid Ultrasound An ultrasound of the thyroid gland can assess its size, structure, and any abnormalities.

What Are the Health Complications of an Untreated Hypothyroidism?

If left untreated, hypothyroidism can lead to various health complications that can affect various systems in the body. Addressing hypothyroidism with proper medical treatment is important to prevent these potential complications. Some of the complications that can arise from untreated hypothyroidism include:

Cardiovascular Issues

Hypothyroidism can lead to elevated levels of cholesterol and triglycerides, increasing the risk of heart disease, heart attacks, and atherosclerosis.

Mental Health Changes

Untreated hypothyroidism can lead to cognitive impairment, memory problems, and depression.

Myxedema Coma

In severe and long-standing cases of untreated hypothyroidism, a rare but life-threatening condition called myxedema coma can occur. It involves severe impairment of mental function, low body temperature, and other organ system failures.


In some cases of hypothyroidism, the thyroid gland might enlarge to produce more hormones. This can result in a visible swelling in the neck called a goitre.

Infertility and Menstrual Irregularities

Hypothyroidism can lead to menstrual irregularities in women and, in severe cases, can contribute to infertility.

Pregnancy Complications

Untreated hypothyroidism during pregnancy can lead to complications such as preeclampsia, preterm birth, and developmental issues in the baby.

High Blood Pressure

Hypothyroidism can contribute to increased blood pressure, raising the risk of hypertension.

Obesity and Weight Gain

Untreated hypothyroidism can lead to persistent weight gain and obesity due to a slower metabolism.

Peripheral Neuropathy

Nerve damage, known as peripheral neuropathy, can occur in untreated hypothyroidism, leading to symptoms such as tingling, numbness, and pain in the extremities.

Dry Skin and Hair Problems

Chronic dry skin and hair problems can become more pronounced without proper thyroid hormone levels.

Constipation and Digestive Issues

Slower digestion due to decreased metabolic activity can lead to chronic constipation and other digestive problems.

Muscle Weakness and Joint Pain

Muscular weakness and joint pain can become more pronounced without appropriate treatment.

Cold Intolerance

A lower basal metabolic rate from untreated hypothyroidism can cause heightened sensitivity to cold temperatures.

Dr. Cho Li Wei 朱丽薇医生

Consultant Endocrinologist
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