All About Thyroid

All About Thyroid

Created On
Apr 12 2018
Last Updated
Dec 08 2022

You will learn about: hypothyroidism; hyperthyroidism; thyroid stimulation hormone (TSH); thyroxine (T4); symptoms of thyroid problems; thyroid disorder in women, children and during pregnancy; at home thyroid test; autoimmune diseases; Hashimoto thyroiditis; Grave’s disease; iodine function; foods for healthy thyroid.


Thyroid is a butterfly-shaped gland in the throat. It's important for mental health, good appetite, optimal energy levels, a healthy sex drive, and heart health. It also helps in metabolism and maintaining the body temperature.

In hypothyroidism, an under-active thyroid slows down metabolism causing fatigue, anxiety, weight gain, slow reflexes, allergies, and poor health.

In contrast, an over-active thyroid in hyperthyroidism causes hyperactivity, nervousness, irritability, insomnia, brittle nails, increased sweating, diarrhea, and excessive bowl movement.

Thyroid releases two key hormones: T4 (thyroxine) and T3 (tri-iodo-thyronine)–with four and three iodine atoms, respectively.

The pituitary gland releases another hormone called TSH (thyroid stimulating hormone) which regulates T3 and T4 levels. Normal TSH levels are key to a healthy mind and body.

If there is a problem—e.g., when our own immune system attacks thyroid gland, the body produces TPO antibodies (anti-thyro-peri-oxidase). Therefore, presence of TPO antibodies in a blood test is indication of autoimmune disease.

A simple at-home thyroid test with a finger prick sample can measure TSH, fT3, fT4, and TPO antibodies.

Thyroid Gland

Thyroid is a small, butterfly-shaped gland that sits in the throat just below the Adam’s apple.

It releases two hormones crucial to our health. They help maintain weight and energy levels because of their unique ability to control metabolism. The thyroid hormones also affect mental health, appetite, energy levels, sleep, sex drive, and overall mood.

Thyroid gland is also responsible for regulating body temperature. That's why feeling of being unusually cold or hot are first signs of thyroid dysfunction.

An under-active gland slows down metabolism, causing a wide range of issues that include weight gain, fatigue, anxiety, skin rashes, high cholesterol, fluid retention and a general feeling of unhappiness.

However, an over-active gland has totally opposite effect: an overactive metabolism with persistent hunger and fatigue. The symptoms of these excess hormones include hyperactivity, nervousness, irritability, insomnia, brittle nails, increased sweating, diarrhea, and excessive bowl movement.



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Thyroid Hormones

There are two main thyroid hormones:

  • T3 (tri-iodo-thyronine) – contains three iodine atoms

  • T4 (thyroxine, or tetra-iodo-thyronine) – contains four iodine atoms

Almost 80 percent of thyroid hormones in the body are available as T4. However, T3 is the active form and readily converts to Thyroxine (T4), by adding one iodine atom.

An enzyme, called Selenium-iodinase–that contains minerals Zinc and Selenium–helps in this of iodination. Therefore, both Zn and Se are critical for a healthy thyroid and interference in their supply, e.g., by excess copper that might bind with Zn, can interfere in this conversion.

A third hormone, called calcitonin, and useful in calcium absorption, is also released by the thyroid gland. Calcitonin is different from parathyroid hormone–also important in calcium absorption. The later is produced by parathyroid glands located behind the thyroid gland.

TSH (thyroid stimulating hormone) is not produced by the thyroid, but pituitary in the brain. However, it's a critical hormone that regulates thyroid function, and is often the first marker in a lab report to diagnose thyroid disorders.

Key thyroid hormones and their healthy ranges: chart of TSH levels and free T3, T4, and TPO antibodies


Thyroid Hormone Production

Based on the mood, time of the day, and other daily activities, hypothalamus in the brain senses a need for thyroid hormones and directs the pituitary glad through a hormone called thyroid-releasing hormone (TRH). The pituitary releases TSH, which thyroid gland in the throat recognizes to release the thyroid hormones, T3 & T4. Hypothalamus monitors them and tweaks the TRH levels accordingly.

It is a closed feedback loop of TSH, T3, and T4 levels that tightly controls thyroid function.

Therefore, a thyroid hormone test should check all three: TSH, T3, and T4, to assess the health of the HPT (hypothalamus-pituitary-thyroid) axis.

Whenever there is a problem in the HPT axis–especially when our own immune system attacks the thyroid gland, the body produces antibodies called TPO (anti-thyro-perioxidase or antithyroid microsomal antibody). It's a good idea to also check TPO antibody levels using a comprehensive test.


Thyroid disorders are fairly common–affecting almost 1 in 25 people with low or high levels.

What is hypothyroidism?

Deficiency of thyroid hormones due to insufficient production of the two hormones in thyroid gland is hypothyroidism.

It can develop due to problems with thyroid gland, pituitary gland, or hypothalamus since all of them are responsible for producing these hormones.

  • Early signs are mild and hard to pinpoint to any specific parts of the body since thyroid hormones affect the whole body.

  • People often disregard symptoms as due to old age, fibromyalgia, menopause, recent pregnancy, or stress in life.

  • The most common feature of hypothyroidism is weight gain.

  • Approximately 2% of population has severe hypothyroidism and 7-15% has mild thyroid problems.

  • Low levels of thyroid hormones occur during times of stress or times of life events when body tries to compensate for any fluctuations in thyroid hormones; typical events for the onset of hypothyroidism are menopause, pregnancy, postpartum.

  • The list of signs and symptoms of thyroid problems is long as thyroid hormones affect every aspect of the body and can overlap other health conditions.

  • Subclinical hypothyroidism is a mild disorder more commonly found in older population where the free-T4 levels are normal but TSH levels are elevated. Almost no symptoms of hypothyroidism are observed at the time but chances of developing them in future are high.

  • Thyroid nodules are abnormal lump-like growths in the thyroid glands. They are not always problematic and should be carefully examined by an endocrinologist.

Our risk of hypothyroidism is highest under 20-years and over 60-years of age.


What are the symptoms of hypothyroidism?

The most important symptoms of hypothyroidism or low thyroid hormones are weight gain, slow metabolism, and fatigue. Here are some of the symptoms in detail:

  • Weight gain – caused by a vicious cycle when low thyroid hormones slow down the metabolism and the body starts to store extra calories which cause other hormone problems (e.g., insulin resistance) that result in further weight gain.

  • Loss of appetite – slow metabolism due to low thyroid hormones results in the brain slowing down the appetite centers.

  • Premature aging – appearance of old, tired, puffy face, bloating, and slurring while speaking.

  • A lot of menopausal symptoms in women are also due to undiagnosed thyroid disease.

  • Goiter – is an enlargement of thyroid gland due to hormone deficiency (or other reasons). It is one of the many symptoms suggestive of thyroid problems but may not be the only reason.

  • Hypothyroidism causes stiff joints and pain and soreness in muscles, symptoms overlapping with arthritis.

  • Feeling cold – slow metabolism creates less body heat giving a feeling of being cold. It also causes blood vessels in the skin to constrict making it cool to the touch.

  • Decreased sweating – due to less body heat from slow metabolism.

  • Constipation – hypothyroidism causes slowing of bowel function resulting in hard, painful bowel movements and bloating.

  • Loss of memory and inability to concentrate – due to slow metabolism and fatigue, memory is sacrificed in favor of other brain functions. Body starts to focus on sleeping and eating instead of concentrating and remembering. Signs similar to Alzheimer’s disease can be due to severe hypothyroidism, e.g., forgetfulness, inability to concentrate, diminished intellectual function, speech capability, and even energy, libido, and motivation problems.

    More symptoms…

  • Depression – 10-15% of depression patients have hypothyroidism. It causes injury to cells that produce serotonin in brain. Low serotonin results in negative moods, inability to experience pleasure, pessimism, and feeling of inadequacy and doom.

  • Skin problems – low thyroid hormone causes dry and itchy skin that develops cracks. In severe cases excess carotene causes yellow tinge on skin.

  • Slow metabolism also slows down hair growth making them coarse and brittle. Sometimes hair start to fall, often in clumps. People with hypothyroidism frequently loose hair in the outer third of eyebrows. Fingernails also become brittle.

  • Fluid retention – resulting in puffiness in the face or around the eyes, thickening of lips, swelling of hands, feet or legs.

  • Heart problems – fluid retention and buildup around heart weakens it causing it to swell, which interferes with pumping of blood.

  • High cholesterol – in general low thyroid hormones cause higher cholesterol.

  • High blood pressure – both high and low thyroid hormones cause high blood pressure.

  • Cardiovascular diseases – low thyroid causes the bad cholesterol (LDL) to rise. Fluid build up around heart can reduce its ability to pump blood. Increased thyroid hormone speeds up the heart and strengthens its pumping action. Therefore a sudden increase in metabolism due to thyroid hormone increase can strain the heart and cause a heart attack.

  • Menstrual problems and infertility – Thyroid hormone controls muscle contraction in the uterus. Without proper muscle contractions periods may become longer and heavier, and may be prolonged becoming irregular. Without proper contraction bleeding may not stop. In some cases ovaries may not be able to release the egg.

  • Gruff or hoarse voice – thickening and swelling of vocal cords results in hoarse, husky, gravelly sound.

    Few other symptoms…

  • Anemia – the low red blood count of anemia can sometimes be caused by hypothyroidism.

  • Slow reflexes – a key sign of hypothyroidism. The relaxation phase of a reflex slows down when a doctor hits the knee with a reflex hammer. The return of knee to resting position shows delay and experienced endocrinologists use this as the most sensitive way to determine subtle deficiencies.

  • Snoring or sleep apnea – excess tissue in neck can interfere with breathing that can cause snoring and poor sleep.

  • Allergies – many people notice worsening of their allergies due to low thyroid hormones.

What are the causes of hypothyroidism?

  • Hashimoto’s disease – the most common cause of hypothyroidism that affects approximately 15 million people in US. This happens when our own immune system attacks the thyroid glands. It is seven times more common in women and is often hereditary.

  • Other forms of damage to thyroid glands – for example, after pregnancy or defects in enzymes necessary for thyroid hormone production.

  • Damage to hypothalamus or pituitary glands – by tumor, infection, or surgical removal.

  • Drugs – lithium is known cause of hypothyroidism and drugs containing lithium or iodine can cause problems.

  • Toxins & pollutants – carbon tetrachloride in drinking water; PCB (poly chlorinated biphenyl) in plastics; a chemical called glyphosate in the common weed killer RoundUp; cadmium in tobacco and sometimes in dried fruits that are dried on galvanized chicken wire (which contains cadmium); triclosan in antibacterial soaps, toothpastes, and dishwashing liquids.

  • Excess iodine – shuts down the thyroid glands by overwhelming it.

  • Radioactive treatments and exposure to nuclear waste.

  • Dietary causes – excess consumption of uncooked vegetables from Brassica family (broccoli, cauliflower, Brussels sprouts, cabbage, mustard, kale, radishes, turnips); there is no issues when one cooks them or consumes in small quantities.

  • Pregnancyhypothyroidism in pregnancy is a serious issue and an estimated 2.5% women have some form of it. But hormone changes may make it difficult to assess. It can have serious intellectual and developmental defects in the baby; that’s why testing every 6-8 weeks during pregnancy is usual; however, it is a serious problem in developing countries.

What is hyperthyroidism?

Production of excess thyroid hormone is hyperthyroidism. Stress is one of the key causes of hyperthyroidism. However, it is less common than hypothyroidism.

The risk of hyperthyroidism is highest for youth and elderly.


What are the symptoms of hyperthyroidism?

  • Symptoms are usually opposite of hypothyroidism, e.g., fast metabolism, and weight loss.

  • One of the primary symptoms is uncontrollable appetite and people with hyperthyroidism always feel hungry.

  • Increased appetite sometimes can result in high calorie consumption which may result in increased weight.

  • The fast metabolism makes one feel hot, hyperactive, irritable, nervous, and symptoms of increased sweating, tremors, heart palpitations, insomnia, brittle nails, diarrhea, more frequent bowels – all symptoms opposite of hypothyroidism.

  • Fatigue is observed in both cases due to body being busy fighting under or over production of thyroid hormones.

What is the role of Iodine in thyroid hormones?

  • The primary role of iodine in our body is to make thyroid hormones. As much as 75% of body’s iodine is in the thyroid glands.

  • Both low and high amounts can damage the thyroid glands.

  • Insufficient amount of iodine results in swelling of gland, resulting in a condition called goiter where the throat becomes abnormally large.

  • High levels of iodine can cause thyroid dysfunction by shutting down the glands completely.

  • Excess iodine symptoms include headaches, vomiting, mouth sores, metallic taste in mouth, swollen salivary glands and rashes. This happens when consuming supplements such as kelp or pills which release a huge burst of iodine in a short period.

  • The recommended daily allowance (RDA) of iodine is approximately 150 microgram per day. One tablespoon of iodine salt contains almost 300 microgram.

  • On an average, people in US consume 300-700 microgram of iodine per day.

  • The main source of iodine in diet is iodized-salt. There is no iodine in sodium chloride (table salt), and it is specifically added for iodine supply.

  • The free running and kosher salts can help reduce this daily excess of iodine, if required.

  • Other natural sources of iodine include: seafood and sea vegetables, preservatives, red dye # 3 (in red, orange, or brown processed foods, pills, capsules), thyroid support formulas (kelp, bugleweed, bladderwrack).

  • Other foods that contain iodine are: seaweed sushi wraps, dairy products, commercially baked goods, snack foods, egg yolks, chocolate, molasses, soy products, rhubarb, potato skin, and foods grown near the coast.

  • Pregnancy and breast feeding require higher iodine in the daily diet.

How to test for thyroid diseases?

It is tricky to diagnose thyroid hormone imbalance just from its symptoms due to various reasons:

  • Ranges for thyroid blood test results are very narrow.

  • Symptoms overlap with other conditions and one may dismiss them as due to other problems.

  • The best test for thyroid function is a blood test which checks for TSH, T3, T4, and TPO.

  • Such a thyroid blood test for low thyroid function, during early or late stage of thyroid deficiency or an immune attack, on the body can check thyroid disorder.

  • Where can I get a thyroid test? An at-home thyroid test can let you collect a sample from home and get results in less than a week.

What does a thyroid test measure?

There are four key markers that should be part of a comprehensive thyroid test:

  • TSH: first indication of thyroid problem is changes in TSH hormone. For an under-active thyroid, TSH levels will rise to stimulate the thyroid to produce thyroid hormones. If problems with thyroid continue, abnormal thyroid hormone levels will be observed. But not in the early stage when they can be compensated by extra TSH. Measure TSH during the day time as TSH levels often surge at night even in healthy conditions.

  • fT3 (free T3 or tri-iodo-thyronine) – of the two thyroid hormones released by the thyroid glands, 20% is T3 and 80% is T4. The T4 converts to the active T3 form. However, both T3 & T4 are bound to a protein called TBG (thyroid-binding globulin). Only the free form is active and it is the best indicator for potency of that hormone. The test will measure the amount of free T3 in the blood.

  • fT4 (free T4 or thyroxine) – only about 1% of T4 is unbound and free to be converted into T3 and the test will measure this free form.

  • Antibodies (TPO, thyroid peroxidase or antithyroid microsomal antibody) – the most common cause of thyroid problems is autoimmune disorder when our own immune system attacks the thyroid gland. The presence of high levels of antibodies will indicate an immune system attaching these glands. Normal TSH levels but high TPO values may indicate other autoimmune diseases.

How to maintain healthy thyroid?

  • Eating lots of fruits and vegetables – as they have anti-oxidants (e.g., beta-carotene, vitamin A, vitamin C). The anti-oxidants are useful for cleaning up oxygen-rich free radicals that hinder the immune system. Immune system attack is one of the main causes of hypothyroidism.

  • Foods high in Selenium and Zinc – both minerals are anti-oxidants and also crucial for T4 to T3 conversion.

    • Selenium: found in whole grains, tuna, halibut, mushrooms, oatmeal, wheat germ, sunflower seeds; those with bacterial infection might be deficient as bacteria need Selenium for survival and growth.

    • Zinc: found in beef, herring, maple syrup, turkey, wheat bran, sunflower seeds; children with Down’s Syndrome and people with obesity tend to have lower levels of Zinc. For other foods and supplements, check this list from Cognitune.

  • Not eating too many raw goitrogens – these are food sources that contain iso-thio-cyanates that interfere with gland functioning. They include cruciferous vegetables from the Brassica family, e.g., cabbage, broccoli, Brussels sprouts, turnips, rutabaga, mustard, kohlrabi, radishes, cauliflower, cassava, millet, and kale. They only cause problems when eaten in large quantities and raw.

  • Peaches, peanuts, pine nuts, spinach, and strawberries can also inhibit thyroid function when eaten in large amounts. There is no need to eliminate these food items from diet but it helps if one avoids eating in large quantities and over a long period.

  • Avoid excessive soy in diet – soy is one of the best natural sources of protein that is also vegetarian and vegan. But the estrogen-like compounds in it can block absorption and action of thyroid hormones when consumed in excess.

    More recommendations…

  • Physical activity – regular exercise is critical for hormone balance and healthy metabolism. It is best to exercise during a time of the day when your energy levels are at their peak.

  • Stress reduction – stress can cause improper functioning of thyroid hormone, slower metabolism, and weight gain.

  • Excess iodine from dietary supplements, e.g., kelp, bugleweed, bladderwrack can interfere with thyroid function.

Key risk factors for hypothyroidism and hyperthyroidism.


Main Source: Hormone Balance by Scott Isaacs, MD