What Is Hypothyroidism? Symptoms, Causes and Treatment

Health and Nutrition

Thyroid gland makes hormone, thyroxine, which affects a person’s physical energy, their weight and their mood. It is located in the front portion of the neck. Thyroid gland takes iodine supplied by the diet and synthesizes thyroid hormone (1). 


Among the energy regulating hormones thyroid hormone is the most important hormone. Thyroid hormone can increase the rate of metabolism and plays an important role in growth the process. 


Thyroid hormone thyroxine


Thyroid hormone is made from iodide and tyrosine, an amino acid. Thyroid hormone thyroxine is also called T4 as it contains four iodine atoms. The active form of T4 is T3 which is also known as triiodothyronine and it is formed by removal of one iodine atom from T4 (2). 


Thyroid stimulating hormone


The quantity of thyroxine secreted by the thyroid gland is regulated by thyroid stimulating hormone (TSH). TSH is secreted by the pituitary gland which is present at the base of the brain. The amount of TSH pituitary gland releases into the blood stream depends on the amount of T4. If there is less thyroxine being secreted by the thyroid gland then the TSH secreted will be more (2).  




An underactive thyroid gland does not make sufficient thyroid hormones essential for the body to function. This condition is known as hypothyroidism. The way the body uses energy is controlled by thyroid hormones, therefore every function of the body is dependent on thyroid hormones (3). 

When the thyroid gland becomes underactive many of the functions of the body slow down.


Causes (3, 4, 5)

Hashimoto’s disease

It is the most common reason for hypothyroidism.  Hashimoto’s disease is an autoimmune disorder where the thyroid gland cells are attacked by the immune cells of the body which leads to a decrease in hormone secretion.


This is a condition in which the thyroid gland becomes inflamed and does not produce enough hormones.


Sometimes babies are born with an under functioning or not fully developed thyroid.

Other reasons

There may be other reasons for hypothyroidism such as removal of part of the thyroid gland surgically, viral infections, certain medication which may affect thyroid function or radiation treatment of thyroid.


The symptoms of hypothyroidism vary from individual to individual (3, 4, 6). The symptoms may differ based on age, gender and other factors. Some of the common symptoms observed in people with hypothyroidism are

  • fatigue
  • weight gain
  • mental slow down
  • sensitive to cold
  • dry skin
  • thinning of hair including eyebrows
  • heavy or irregular menstrual periods
  • fertility issues
  • depression
  • constipation
  • changes in voice



Generally, after diagnosis the doctor will prescribe levothyroxine which will perform the same function as thyroxine in the body (3). The dose will be fixed by the doctor after regular blood tests. The medicine is taken first thing in the morning.

Hypothyroidism is mostly a permanent condition and thyroid hormone replacement therapy is prescribed for life to maintain hormone levels (5).

Final word

Treatment should be under the supervision of your doctor. Never stop taking the medicine or change the dosage without your doctor’s knowledge. 




  1. Centers for Disease Control and prevention (2014). HTDS Guide – About Thyroid Disease: Section Summary.



  1. American Thyroid Association (2014).Thyroid Function Tests.



  1. National Institute of Diabetes and Digestive and kidney diseases (2016). Hypothyroidism (Underactive Thyroid)



  1. National Health Service (2018). Underactive thyroid (hypothyroidism)



  1. Drake, M. T. (2018) Hypothyroidism in Clinical Practice, Mayo Clinic Proceedings. Vol. 93 (9).



  1. Chaker, L., Bianco, A. C., Jonklaas, J. and Peeters, R. P. (2017) Hypothyroidism, Lancet. Vol. 390 (10101).

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