Thyroid Hormones


The thyroid gland uses iodine to produce thyroxine (T4) and triiodothyronine (T3), the two main thyroid hormones. The thyroid gland also produces the hormone called calcitonin, which is involved in calcium metabolization and stimulating bone cells to add calcium to bone.

What is Thyroxine (T4) and Triiodothyronine (T3)?

Thyroxine plays a role in regulating many bodily functions, including digestive function, metabolism, brain development, bone health and muscle control. T4 also affects body temperature, growth, and heart rate. Once the thyroxine is in the bloodstream, it travels to vital organs, such as the liver and kidneys, and is converted into triiodothyronine (T3).

Too much or too little thyroxine can cause a variety of health problems. If the thyroid releases too much thyroxine (a condition called thyrotoxicosis), then the individual may develop a goiter, menstrual irregularities, weight loss, increased bowel movements, heat intolerance, irritability and fatigue. Thyrotoxicosis may be caused by thyroid inflammation, hyperthyroidism, or tumors in the thyroid gland.

If the thyroid gland produces too little thyroxine (a condition called hypothyroidism) may cause developmental problems in young individuals. Hypothyroidism may lower the metabolic rate and cause memory problems, weight gain, fatigue, infertility and muscle stiffness.


What is Calcitonin?

Calcitonin is produced and released by the C-cells in the thyroid gland. Calcitonin works to balance out the effects of the parathyroid hormone and regulate the blood’s calcium and phosphate levels.

This hormone inhibits the activity of the osteoclasts, which are the cells that break down the bone. By preventing the breakdown of bone, calcitonin helps decrease the amount of calcium in the blood. Calcitonin also works to decrease the amount of calcium the kidneys can re-absorb.

The body regulates secretion of calcitonin by measuring the blood’s calcium levels. If levels of calcium increase, the body reacts by increasing levels of calcitonin.

Though doctors are aware of what calcitonin does, its importance is not well understood. High or low levels of calcitonin don’t appear to cause any symptoms or impair bodily functions.

Signs of Thyroid Hormone Imbalance

Individuals experiencing the following symptoms may have a health condition affecting the thyroid:

  • Fatigue
  • Depression
  • Anxiety
  • Change in appetite or taste
  • Difficulty concentrating
  • Forgetfulness
  • Low libido
  • Weight gain
  • Body aches and pains
  • Heart palpitations
  • Dry skin
  • Constipation
  • Pain in the extremities or muscles
  • High or low blood pressure
  • Feeling cold or hot
  • Hoarseness
  • Insomnia
  • Weight gain or weight loss
  • Hair loss
  • Infertility
  • High cholesterol

When to Consult a Doctor

Patients experiencing symptoms of a thyroid disorder should schedule an appointment with their physician and request a thyroid stimulating hormone (TSH) test, Free T3, and Free T4 tests. Based on the results of the tests, the physician may recommend thyroid hormone replacement therapy.

What is Thyroid Hormone Replacement Therapy?

Thyroid hormone replacement therapy involves taking pure, synthetic thyroxine (T4) to balance out hormone levels and replicate normal thyroid functioning. The only safety concern with thyroid hormone replacement therapy is identifying the right amounts to take. Patients may need to make multiple visits to the doctor’s office to pinpoint the correct dosage.