What is hypothyroidism?

Hypothyroidism is when the thyroid gland does not produce enough thyroid hormones to meet the needs of the body. The thyroid is underactive.

The opposite is hyperthyroidism, where the thyroid produces too much thyroid hormone. However, the link between hyperthyroidism and hypothyroidism is complex, and one can lead to the other, in certain circumstances.

Thyroid hormones regulate metabolism, or the way the body uses energy. If thyroxine levels are low, many of the body’s functions slow down.

About 4.6 percent of the population aged 12 years and above in the United States has hypothyroidism.

The thyroid gland is found in the front of the neck below the larynx, or voice box, and has two lobes, one on each side of the windpipe.

It is an endocrine gland, made up of special cells that make hormones. Hormones are chemical messengers that relay information to the organs and tissues of the body, controlling processes such as metabolism, growth, and mood.

The production of thyroid hormones is regulated by thyroid-stimulating hormone (TSH), which is made by the pituitary gland.

This, in turn, is regulated by the hypothalamus, a region of the brain. TSH ensures that enough thyroid hormones are made to meet the needs of the body.

Fast facts on hypothyroidism

  • The thyroid gland produces two thyroid hormones, TS3 and TS4.
  • These hormones regulate the body’s metabolism.
  • The most common cause of hypothyroidism in the U.S. is Hashimoto’s disease.
  • Symptoms of hypothyroidism include fatigue, cold intolerance, and joint and muscle pain.


Hypothyroidism refers to the underproduction of hormones in the thyroid gland. It has a wide range of symptoms.
Thyroid hormones affect multiple organ systems, so the symptoms of hypothyroidism are wide-ranging and diverse.

The thyroid creates two thyroid hormones, triiodothyronine (T3) and thyroxine (T4). These regulate metabolism, and they also affect the following functions:
* brain development
* breathing
* heart and nervous system functions
* body temperature
* muscle strength
* skin dryness
* menstrual cycles
* weight
* cholesterol levels
Symptoms of hypothyroidism commonly include, but are not limited to:
* fatigue
* weight gain
* cold intolerance
* slowed heart rate, movements, and speech
* joint and muscle pain, cramps, and weakness
* constipation
* dry skin
* thin, brittle hair or fingernails
* decreased sweating
* pins and needles
* heavy periods, or menorrhagia
* weakness
* high cholesterol
* puffy face, feet, and hands
* insomnia
* balance and co-ordination issues
* loss of libido
* recurrent urinary and respiratory tract infections
* anemia
* depression
If left untreated, the following symptoms can manifest:
* hoarseness
* puffiness in the face
* thinned or missing eyebrows
* slow heart rate
* hearing loss
If it develops in children or teenagers, the signs and symptoms are generally the same as adults.
However, they may also experience:
* poor growth
* delayed development of teeth
* poor mental development
* delayed puberty