Q.Which disease is caused by iodine deficiency?

Thyroid Disorders: When the Body's Thermostat Goes Wrong

Think of the thyroid gland as your body's thermostat. It sits at the front of your neck, shaped like a butterfly, and its job is to set the metabolic "temperature" — how fast or slow every cell in your body works. The two hormones it releases, thyroxine (T4) and triiodothyronine (T3), control everything from heart rate and digestion to brain development and body temperature.

When the thermostat works perfectly, your metabolism hums along at a steady pace. When it breaks, you get one of two problems: too little hormone (hypothyroidism) or too much (hyperthyroidism).

Hypothyroidism: The Engine Running Too Slow

In hypothyroidism, the thyroid gland produces insufficient T3 and T4. The body's metabolic rate drops. Everything slows down.

What Causes It?

The most common cause worldwide is iodine deficiency. Iodine is an essential raw material for making thyroid hormones — without it, the gland cannot produce enough. The gland tries to compensate by growing larger, leading to a goitre (a visible swelling in the neck). In regions where iodine is scarce in the soil and water, this is widespread.

Other causes include autoimmune destruction (Hashimoto's thyroiditis), where the body attacks its own thyroid tissue, or surgical removal of the gland.

The Three Key Manifestations

1. Goitre — This is the enlarged thyroid gland itself. It appears as a swelling in the front of the neck that moves when you swallow. The gland is working overtime, trying to squeeze out enough hormone from limited raw materials. In iodine deficiency, the gland can become quite large.

2. Cretinism — This occurs when hypothyroidism develops during infancy or early childhood. Thyroid hormones are absolutely critical for brain development and skeletal growth. Without them, a child suffers:

• Severe mental retardation
• Stunted physical growth (dwarfism)
• Coarse facial features, thick tongue, protruding abdomen
• Delayed bone age and sexual development

This is entirely preventable with early diagnosis and treatment — which is why newborn screening for thyroid function is standard in many countries.

3. Myxoedema — This is the adult form of severe, long-standing hypothyroidism. The name comes from the characteristic swelling of the skin and underlying tissues, caused by accumulation of a jelly-like substance (mucopolysaccharides) in the connective tissue. The face becomes puffy, the eyelids swollen, the voice hoarse. Other features include:

• Extreme fatigue and lethargy
• Cold intolerance (you feel cold when others are comfortable)
• Weight gain despite poor appetite
• Constipation, slow heart rate, depression
• Thinning hair and dry, coarse skin

In its most severe form, myxoedema coma is a medical emergency — the patient becomes unconscious, hypothermic, and bradycardic.

Hyperthyroidism: The Engine Running Too Fast

In hyperthyroidism, the thyroid produces excess T3 and T4. The metabolic rate skyrockets. Everything speeds up.

What Causes It?

The most common cause is Graves' disease, an autoimmune condition where antibodies stimulate the thyroid to overproduce hormones. Other causes include toxic nodules (lumps in the gland that secrete hormone independently) or excessive iodine intake.

The Clinical Picture

The patient with hyperthyroidism is the opposite of the hypothyroid patient:

• Weight loss despite increased appetite
• Heat intolerance and excessive sweating
• Rapid, forceful heartbeat (palpitations, tachycardia)
• Tremor of the hands, restlessness, anxiety, insomnia
• Bulging eyes (exophthalmos) — a classic feature of Graves' disease, caused by inflammation and swelling of the tissues behind the eyes
• Frequent bowel movements, muscle weakness

The thyroid gland itself may be enlarged (goitre), but unlike the hypothyroid goitre, this one is overactive. …