What Does the Thyroid Do?

What does it do?

The thyroid gland is about 2 inches long and is found in the base of the neck. Its main function is to produce and release two hormones: triiodothyronine (T3) and thyroxine (T4). It mostly produces T4 which is converted into T3 in the liver. Iodine is extracted from the blood to synthesize T3 and T4. The pituitary gland uses thyroid stimulating hormone (TSH) to tell the thyroid how much T3 and T4 to make. These hormones regulate how quickly cells utilize energy, which has far-reaching consequences:

  • Body temperature regulation
  • Attention and reflexes
  • Heart rate
  • Blood pressure
  • Fetal development
  • Childhood growth
  • Digestion
  • Menstrual cycles

Thyroid problems


A goiter is an enlarged thyroid gland and is most commonly a result of iodine deficiency. In the US where iodine is put into water and salt, the more common cause is due to the under- or overproduction of T3 and T4 (hypo- and hyperthyroidism, respectively). Some symptoms include difficulty in breathing and swallowing.


When the thyroid produces too much T3 and T4, one may experience these symptoms:

  • Muscle weakness
  • Menstrual irregularity (lighter, less frequent periods)
  • Trouble sleeping
  • Weight loss
  • Heart palpitations
  • Anxiety
  • Increased appetite
  • Irritability
  • Increased perspiration
  • Sensitivity to heat
  • Goiter


When the thyroid produces too little T3 and T4, one may experience these symptoms:

  • Weight gain
  • Muscle weakness and/or pain
  • Fatigue
  • Thinning/loss of hair
  • Impaired memory
  • Lowered heart rate
  • Higher cholesterol
  • Sensitivity to cold
  • Leg swelling
  • Heavy/irregular periods
  • Goiter


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