Understanding thyroid hormones and its effect on your body

The Biomarker Handbook is a curated series that seeks to provide readers with insights on each biomarker we cover in our blood test packages and its relation to our body.


Triiodothyronine (T3) and thyroxine (T4) are the 2 major hormones produced by the thyroid gland (a butterfly shaped organ located at the base of the throat). Together these thyroid hormones help regulate the rate of energy usage by the body (otherwise known as metabolism).

Almost all (95%) of the thyroid hormones – triiodothyronine and thyroxine – are bound to protein, while the remaining (5%) are free. These free form are biologically active. The amount of thyroid hormones (T3 and T4, bound and unbound) can be easily measured by a simple blood test, commonly called thyroid function test.

T4 is known as a pro-hormone, which is converted into T3 T4 in the liver or other tissues. T3 has a greater metabolic activity than T4, but possesses a shorter half-life.

T4 production is regulated by a feedback system. When the T4 level in the blood decreases, the hypothalamus gland in your brain releases a homrone called TRH, which stimulates the pituitary gland to produce and release thyroid-stimulating hormone (TSH). TSH then stimulates the thyroid gland to make and/or release more T4. As the blood concentration of T4 increases, TSH release is inhibited.

Why is it important to track these biomarkers?

These markers (T3, T4, and TSH) allow proper evaluation thyroid gland function, diagnose thyroid disease, determine the cause, and monitor effectiveness of treatment for thyroid disorders.  These hormones regulate the metabolism of all our cells, affect protein synthesis, help regulate long bone growth (synergy with growth hormone) and nerve cell maturation, and increase the body’s sensitivity to catecholamines (such as adrenaline).

Thyroid function abnormality is a relatively common finding in our general population, yet many people do not even know they suffer from it. This is the perfect situation for screening and tracking a biomarker. It is a common problem, without symptoms in early stages, and treatable. It is very important to diagnose any underlying abnormalities and manage them accordingly, together with regulating the hormonal levels in your blood.

Hypothyroidism and hyperthyroidism

When your thyroid hormone levels are below normal, it is termed hypothyroidism. This is when the thyroid gland is said to be under-active. When the thyroid hormone levels are above normal, it’s known as hyperthyroidism. This is when the thyroid gland is said to be overactive and produces more than enough hormones.

Both of these are conditions should be investigated and managed by your doctor, because when left untreated can have long term consequences to health not just from the high or low thyroid effects, but also from the disease causing the high or low hormonal state.

Diseases that cause hypothyroidism and hyperthyroidism

Autoimmune hypothyroidism, also known as Hashimoto’s thyroiditis, is the most common cause of hypothyroidism. Autoimmune disorders occur when your immune system produces antibodies that attack your own tissues.

Hypothyroidism may also be caused by other reasons:

  • Anti-thyroid medications. People who produce too much thyroid hormone (hyperthyroidism) are often treated with radioactive iodine or anti-thyroid medications to reduce and normalise their thyroid function. However, in some cases, treatment of hyperthyroidism can result in permanent hypothyroidism.
  • Other medications. Non-thyroid medications that can affect your thyroid gland function include Amiodarone (used to treat abnormal heart rhythms), lithium (for bipolar disorder and depression), Interleukin (for cancer treatment), Interferon-Alpha (for hepatitis and cancer).
  • Radiation to the head or neck. During cancer treatment with radiation, your thyroid gland can be affected.
  • Thyroid surgery. Removing all or a part of your thyroid gland can reduce or stop thyroid hormone production. In that case, you’ll need to take thyroid hormone for life.
  • Less commonly, diseases such as congenital hypothyroidism (many parts of the world screen newborns for this); pituitary gland disease (leading to reduced TSH production); pregnancy (again many parts of the world screen the pregnant women for thyroid function abnormality); iodine deficiency or toxicity.

If left untreated, hypothyroidism can lead to several complications such as goiter (enlarged thyroid gland, which can cause difficulty swallowing and breathing); heart disease both directly causing an enlarged heart and heart failure, or indirectly through an associated high LDL (bad cholesterol); general mental slowness and even depression; peripheral nerve damage, muscle weakness; myxedema; infertility and birth defects.

 Hyperthyroidism can be caused by a range of conditions, including:

When left untreated, hyperthyroidism can lead to a number of complications such as heart disease (abnormal and fast rhythm, heart failure) which is reversible if treated; brittle bones (osteoporosis); eye problems (double, blurred or total loss of vision); red and swollen skin; thyrotoxic crisis (sudden worsening of delirium, fevers, or rapid pulse- seek immediate medical care).

Signs and symptoms of hypothyroidism

If you suffer from a combination of these symptoms or signs, you may well have an underactive thyroid and should seek medical advice.

  • Fatigue
  • Heightened sensitivity to cold
  • Weight gain
  • Constipation
  • Dry skin
  • Hoarseness
  • Puffy face
  • High cholesterol levels
  • Impaired memory
  • Muscle weakness
  • Muscle aches, stiffness and tenderness
  • Swelling and pain the joints
  • Thinning hair
  • Irregular menstrual periods
  • Depression
  • Slowed heart rate

Signs and symptoms of hyperthyroidism

When you see a combination of several of these symptoms or signs, you may well have an overactive thyroid. Seek medical help.

  • Rapid heartbeat, also known as tachycardia, which can be irregular
  • Sudden and unexplained weight loss
  • Increased appetite
  • Tremor
  • Nervousness, irritability, anxiety
  • Sweating
  • Sensitivity to heat
  • Changes in menstrual patterns
  • Changes in bowel patterns, specifically more frequent bowel movements
  • Fatigue
  • An enlarged thyroid gland
  • Difficulty sleeping
  • Skin thinning
  • Fine, brittle hair

Natural ways to prevent or treat hypothyroidism

Hypothyroidism can be treated with a proper diet in combination with medical advice. The following are helpful:

  • Wild-caught fish such as Alaskan salmon, Pacific sardines and Atlantic mackerel
  • Coconut oil
  • Probiotic-rich foods, such as, organic goat’s milk yogurt, kefir, kombucha, kimchi, sauerkraut and natto.
  • Seaweeds such as, Nori, Kelp, Kombu and Wakame.
  • Clean water
  • Sprouted seeds such as Flax, hemp and chia seeds.
  • High-fiber foods. Try to consume more fresh vegetables, beans, berries, lentils and seeds.
  • Bone broth
  • Fruits and vegetables

Foods to avoid: Tap water, goitrogen foods, conventional dairy, gluten, refined flour products, sugar.

The following foods may ease symptoms of hyperthyroidism:

  • Strawberries, blueberries, raspberries.
  • Broccoli
  • Vitamin D and Omega-3. Salmon, eggs, mushrooms, walnuts, olive oil
  • Turkey
  • Yogurt

Foods to avoid with hyperthyroidism are: High-glycemic carbohydrates (sugary sweets, rice, white flour, low-fiber cereals, juices and instant potatoes); goitrogenic foods (broccoli, cauliflower, cabbage, millet and soy); unhealthy fats; caffeine and alcohol.

Tests to diagnose hypothyroidism and hyperthyroidism

  • Medical history and a physical examination by your doctor provide the first clues.
  • TSH blood test; this is generally the first line of screening for an over- or under-active thyroid
  • T3 (triiodothyronine) blood test (both the total, bound and unbound versions)
  • T4 (thyroxine) blood test (both the total, bound and unbound versions)
  • Autoantibodies such as antithyroid antibodies, thyroglobulin antibodies which your doctor may order

Thyroid disease has a deep impact on health and well-being of a person. Worldwide, thyroid diseases continue to be common yet one of the most neglected and under-diagnosed chronic health conditions. People of all races and ages are can be affected by thyroid disease, but women are 5 to 8 times more likely to have it, compared to men. Awareness and knowledge about the disease itself and its treatment is very crucial for satisfactory long-term outcome and compliance.


If you want to learn tips on how to care for your body and your baby during pregnancy, read our lifestyle article here!

Interested in other biomarkers? Check out the rest of The Biomarker Handbook.

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