Thyroid Gland: Facts, function & diseases

illustration of the thyroid gland
(Image credit: Getty Images)

The thyroid gland is a small, butterfly-shaped organ in the throat that is very important to health and wellbeing. The thyroid is part of the endocrine system, which is essentially a collection of glands. These glands produce hormones that regulate mood and other various functions in the body — and the thyroid gland is no different. 

"Thyroid hormones impact a host of vital body functions, including heart rate, skin maintenance, growth, temperature regulation, fertility and digestion,” said the late Dr. Jerome M. Hershman, former emeritus professor of medicine at the David Geffen School of Medicine at the University of California, Los Angeles.

But how big is the thyroid gland? What is its exact function? And what thyroid conditions should you know about? Keep reading to discover everything there is to know about this organ. 

Thyroid gland: Size

The thyroid gland is 2 inches (5 centimeters) wide and weighs between 20 and 60 grams (0.7 to 2.1 ounces), according to the U.S. National Library of Medicine

The gland stretches across the front of the neck, below the voice box. Like a butterfly, it has two wings called lobes that stretch around the windpipe. The wings are connected by a small piece called the isthmus.

Human thyroid gland, illustration.

(Image credit: Getty Images)

Thyroid gland: Function

The thyroid gland controls just about every cell in the human body. It secretes hormones calcitonin, T4 (thyroxine or tetraiodothyronine) and T3 (triiodothyronine) into the bloodstream. The hormones control the rate at which cells and organs turn nutrients into energy and the amount of oxygen cells use. 

"In this way, the thyroid gland is the body's master metabolic control center," said Cindy Samet, a chemistry professor at Dickinson College in Carlisle, Pennsylvania. "Brain, heart and kidney function, as well as body temperature, growth and muscle strength — and much more — are at the mercy of thyroid function."

Cindy Samet
Cindy Samet

Samet has taught at Dickinson College in Pennsylvania since 1988. She attended the college as an undergraduate, majoring in chemistry. Samet then went to graduate school and obtained her doctorate in physical chemistry from the University of Virginia in 1988. Outside of the research laboratory, she studies the chemistry of certain illnesses, such as vitamin B12 deficiency, gluten-related problems and thyroid disease.  

The thyroid also regulates the brain and nerve function and development, plus the function of the skin, hair, eyes, heart and intestines.

The thyroid works in conjunction with the pituitary gland. The pituitary gland regulates how many hormones the thyroid releases. 

The thyroid gland produces a large amount of T4, but that hormone is not very active. T4 is converted to T3 via an enzyme that removes one of its iodine atoms. 

"Although T3 is much more potent than T4, there is much evidence to support that people with hypothyroidism feel much better when they receive a combination treatment that includes a small amount of T3 with the commonly prescribed T4," Samet told Live Science.

Thyroid gland: Diseases and conditions

Thyroid conditions affect an estimated 20 million Americans and as many as 60% of people with a thyroid disease don't know they have a problem, according to the American Thyroid Association

"Women are particularly at risk for a thyroid issue," Hershman said. "One in eight women will develop a thyroid disorder during the course of their lives — that's five to eight times the rate in men."

Graves' disease

One of these conditions is called Graves’ disease, which was discovered by the Irish doctor Robert James Graves in 1835. Graves' disease is an autoimmune disorder. 

The immune system attacks the thyroid gland and makes it become overactive. An overactive thyroid is a condition called hyperthyroidism. A bulge on the neck, called a goiter, is a common symptom. The patient may also experience an increased heart rate, according to the National Library of Medicine (NLM).


Hypothyroidism, also known as underactive thyroid, is the opposite of Graves' disease. It occurs when the thyroid gland does not produce enough hormones. This can cause body functions to slow down or stop completely.  

Thyroid cancer

Cancer is another disease that can affect the thyroid. A 2017 study published in the Journal of the American Medical Association (JAMA) has found that between 1975 and 2013 the number of thyroid cancer cases diagnosed each year has more than tripled. Cases of advanced forms of the disease rose by about 3% each year while deaths rose by about 1% each year. 

A lump or swelling on your thyroid gland is called a nodule. Nodules can be harmless, but some can cause a production of too much hormone or be cancerous, according to the Endocrine Society.  

"Up to 70 percent of middle-age females and 40 to 50 percent of middle-age males have thyroid nodules, said Dr. Melanie Goldfarb, an endocrine surgeon and director of the Endocrine Tumor Program at Providence Saint John's Health Center in Santa Monica, California, and an assistant professor of surgery at the John Wayne Cancer Institute in Santa Monica. "You can also be born with an extra piece anywhere as high up as the base of your tongue,” Goldfarb adds. 

Dr. Melaine Goldfarb
Dr. Melanie Goldfarb

After graduating from Brown University and the University of Illinois College of Medicine, Goldfarb completed her general surgery residency at Harvard Medical School and endocrine surgery fellowship at the University of Miami. Goldfarb has been exclusively practicing endocrine surgery in Los Angeles since 2011. Her expertise is minimally invasive surgery for thyroid cancer and disorders, hyperparathyroidism and adrenal tumors.

In some medical cases, such as cancer, the thyroid is removed. Humans can live without their thyroid if a hormone pill is taken daily.

Promoting good thyroid health

Science tells us that for the thyroid to remain healthy, it needs iodine to produce hormones, but just a little. 

"It turns out that one teaspoonful of iodine is enough for a lifetime of thyroid hormone production. But the thyroid gland needs a constant supply of iodine, so we must intake iodine in some form on a daily basis and not all at once," Samet said. Too much iodine can actually make the thyroid produce less hormones. 

The best way to get iodine is through eating healthy foods, such as seafood and dairy products. You can also get it by seasoning your food with iodized salt.

Additional resources

Alina Bradford
Live Science Contributor
Alina Bradford is a contributing writer for Live Science. Over the past 16 years, Alina has covered everything from Ebola to androids while writing health, science and tech articles for major publications. She has multiple health, safety and lifesaving certifications from Oklahoma State University. Alina's goal in life is to try as many experiences as possible. To date, she has been a volunteer firefighter, a dispatcher, substitute teacher, artist, janitor, children's book author, pizza maker, event coordinator and much more.