Thyroid Hormones 101 – What does a high result mean?

November 17, 2023Hertility

The thyroid is a small gland in your neck, but don’t be fooled by its size. It plays a vital role in the body and keeping it healthy. By producing important hormones, it can affect your heart rate, metabolism (how well and fast your body processes what you eat and drink) and even fertility.

Sometimes the thyroid gland makes too much of these hormones, which can cause a thyroid disorder called hyperthyroidism.

What are thyroid hormones?

But before we get into the details, if you are wondering what thyroid hormones even are, then you can have a quick recap here. 

The thyroid gland is controlled by the hypothalamus and the pituitary gland, located in the brain. 

The hypothalamus releases thyrotropin-releasing hormone (TRH), which stimulates the pituitary gland to release thyroid-stimulating hormone (TSH), which tells the thyroid how much hormone to produce.

The thyroid gland produces 2 main hormones that can impact fertility – Thyroxine (T4) and Triiodothyronine (T3)

T4 is the primary form of thyroid hormone circulating in the blood, to bring about its effects, T4 has to be converted to T3.

When T4 and T3 levels are low in the blood, the brain produces TRH and TSH, which stimulates the thyroid to make more T4 and T3. 

When T4 and T3 levels are too high in the blood, the brain produces less TRH and TSH, which reduces the amount of T4 and T3 produced by the thyroid.

Most thyroid hormones in the blood are bound by the protein Thyroxine-binding globulin (TBG) which is responsible for binding and transporting thyroid hormones to the necessary tissues.  When the thyroid hormones are bound to TBG, they are inactive.

Free thyroxine (FT4) and free triiodothyronine (FT3) are the unbound, free and active forms of thyroid hormones that can enter tissues and bring about an effect in the body.

So what does hyperthyroidism mean?

If TSH levels are low, and levels of T4 (and sometimes T3) are high in the blood, this could indicate that the thyroid gland is making too much thyroid hormone, i.e. it is overactive.  This condition is called primary hyperthyroidism

As the thyroid gland is producing very high levels of hormones, the pituitary gland tries to crank down the amount of TSH it produces.

Early or mild hyperthyroidism which is called subclinical hyperthyroidism may present as low TSH and normal thyroid hormone levels in the blood.

What are the symtoms of hyperthyroidism?

In cases where there is a hormonal imbalance due to hyperthyroidism, it may result in the following symptoms:

  • Rapid heartbeat (tachycardia) — more than 100 beats a minute
  • Irregular heartbeat (arrhythmia)
  • Feeling of having a pounding heart (palpitations
  • Increased blood pressure
  • Muscle weakness
  • Twitching or trembling
  • Difficulty sleeping and insomnia
  • Persistent tiredness and weakness
  • Changes in mood, especially nervousness, irritability restlessness, anxiety and depression
  • Irregular menstrual cycles, decreased menstrual flow (hypomenorrhea) and missed periods (amenorrhea), which may cause fertility issues
  • Frequent bowel movements or diarrhoea
  • Heat intolerance and excessive sweating
  • Increased appetite
  • Unintentional weight loss, even if food intake is the same or increases
  • Hair thinning or hair loss
  • Protruding eyes (exophthalmos)

If you are experiencing any symptoms of these symtoms and want to understand your hormone health, we’re here to get you the answers you deserve. Hertility at-home hormone and fertility testing kits help give you insight into your TSH, FT4 and FT3 levels along with other hormones that can impact your fertility.

But what could be causing your thyroid levels to increase?

   Hyperthyroidism may be caused by underlying health conditions

  • Having a family history of thyroid disease increases your risk of developing a thyroid disorder.
  • Graves’ disease is an autoimmune disorder and is the most common cause of hyperthyroidism.  It is a genetic condition and can be passed from one generation to the other. In Graves disease, the attack by the immune system makes the thyroid gland grown work harder and make more thyroid hormones.

  Did you know?

An autoimmune disorders occur when the immune system produces antibodies that attack someone’s tissues. 

Pernicious anaemia is an autoimmune condition that affects the digestive system and prevents the absorption of vitamin B12, resulting in a deficiency. Vitamin B12 deficiency has also been linked to autoimmune hyperthyroidism.  Being strictly vegetarian or following a vegan diet can increase the risk of Vitamin B12 deficiency. 

Wondering how veganism can impact you on fertility? Read our article on it  here.

Type 1 diabetes has also been linked to an increased risk of developing autoimmune thyroid diseases such as Graves’ disease. 

Did you know?

Type-1 diabetes is an autoimmune condition where the immune system produces antibodies against the pancreas’ insulin-producing cells, meaning the body can no longer efficiently produce its own insulin and  therefore cannot regulate blood sugar levels.

Primary adrenal insufficiency, also known as Addison’s disease, is a rare condition that occurs when the adrenal glands (located on top of the kidneys) are damaged. In most cases, it is caused due to autoimmune reasons when the immune system attacks the healthy adrenal glands by mistake. It has been linked to Graves’ disease. 

Ulcerative colitis is a common form of Inflammatory Bowel Disease (IBD) that is characterised by chronic inflammation and ulcers in the digestive system. It has been linked to Graves’ disease. However, it is uncertain whether this link is due to a specific cause or just a simple coincidence.

People with one autoimmune condition have been found to be at increased of developing other autoimmune conditions as well.
Always Inform your healthcare provider if any autoimmune diseases run in your family.

  • Hyperthyroidism in pregnancy is usually caused by Graves’ disease. High levels of the hormone human chorionic gonadotropin (hCG), which occur during pregnancy, has also been associated with an overactive thyroid gland.
  • Thyroiditis or inflammation of the thyroid gland can cause a brief period of hyperthyroidism followed by the development of hypothyroidism or resolution. It can sometimes be caused due to an infection or develop after giving birth (postpartum thyroiditis).
  • Pituitary dysfunction, such as TSH-secreting pituitary adenomas, are benign (non-cancerous) tumours of the pituitary gland. They can cause excess production of TSH, causing the thyroid gland to enlarge, become overactive and produce excess hormones.
  • With age, lumps or nodules may form in the thyroid gland. They are mainly observed in people over 60 years of age. Usually, they are benign (non-cancerous) and are called thyroid adenomas.  They are rarely active and don’t produce thyroid hormones. 

Sometimes they may become ‘autonomous’, meaning they do not respond to pituitary regulation and start producing thyroid hormones.

If a single nodule is independently producing thyroid hormones, it is called a functioning nodule and results in toxic adenoma, which can easily be detected with a thyroid scan. If there is more than one functioning nodule, it is called a multinodular goitre

  • Rarely, a cancerous thyroid tumour, resulting in thyroid cancer, can affect the production of thyroid hormones.
  • Down’s syndrome is a genetic condition caused by the inheritance of an extra copy of chromosome 21.  It is associated with an increased risk of health conditions, including hyperthyroidism.

Your diet and lifestyle habits can also impact thyroid functions

  • The thyroid uses iodine to make T4, thus the amount of iodine consumed in the diet can affect the amount of T4 made. Excessive iodine intake can result in hyperthyroidism.

Some foods rich in iodine include fish such as cod and tuna, seaweed, shrimp, and other seafood, dairy products such as milk, yogurt, and cheese),

Iodine is also added to some foods such as salt labeled as “iodized”.

  • The thyroid has a higher concentration of selenium than most other organs, meaning it plays an important role in the functioning of the thyroid. 

Selenium deficiency has been associated with larger thyroid volume and a higher prevalence of thyroid enlargement.

Selenium deficiency has been linked to an increased risk of hyperthyroidism, whether from Graves disease or nodular goitre.

  • Copper is the third most abundant mineral in the human body. It plays an important role in thyroid functioning, especially in hormone production and absorption. 

It stimulates the production of T4 and prevents over absorption of it in the blood cells by controlling the body’s calcium levels. 

Hyperthyroidism may be associated with higher copper levels.

  • A magnesium deficiency may increase the risk of developing Graves’ disease and is associated with elevated thyroid antibody levels.
  • Smoking not only increases the risk of developing Grave’s disease but is also associated with faster disease progression, worsening of symptoms, and poorer response to thyroid treatment.

You can read more about the impact of smoking on your hormones here.

Thyroid hormone levels can also rise due to certain medications

  • Sometimes the use of thyroid hormone therapy for hypothyroidism, especially with tetraiodothyronine (T4), can result in hyperthyroidism if the dosage is too high.
  • Amiodarone is used to treat irregular heartbeats. It has a very high iodine content and has been associated with the development of thyrotoxicosis. 
  • Lithium is used to treat mood disorders such as bipolar disorder and depression and decreases thyroid hormone secretion.
  • Metformin is an insulin sensitiser and is often prescribed to manage blood glucose and insulin levels. Some research shows that it might be linked to a slight decrease in TSH levels, especially if you have an underlying thyroid disorder.

Did you know?

 Metformin is also used as a treatment option for those with PCOS to induce ovulation. 

  • Dopaminergic agents are medications that mimic dopamine, a chemical in the brain (neurotransmitter) responsible for many of our daily physical and mental functions.  

These are prescribed when dopamine levels are low, as seen in cases of Parkinson’s disease and restless leg syndrome and have been found to reduce levels of TSH.

  • Octreotide is an injection used to treat acromegaly, a disorder caused by excess growth hormone (GH), increasing the growth of body tissues and causing metabolic dysfunction. It has been shown to reduce TSH production.

Are there any long term risks of hyperthyroidism?

Hyperthyroidism in some cases can increase the risk of developing long term health problems, including:

  • Thyrotoxicosis is a toxic condition that is caused by an excess of thyroid hormones. It can be caused by an excessive intake of thyroid hormones or overproduction of thyroid hormones.
  • Enlargement of the thyroid gland known as goitre. It is an abnormal swelling of the thyroid gland that causes a lump to form in the throat. 
  • Osteoporosis is the thinning of the bones and can increase the risk of fractures. Osteoporosis is often associated with menopause.
  • Cardiovascular problems due to an irregular heartbeat, which can cause atrial fibrillation, a condition that can lead to stroke and congestive heart failure if left untreated.
  • An eye disease called Graves’ ophthalmopathy or thyroid eye disease that can cause double vision, light sensitivity, and eye pain, and rarely can lead to vision loss.
  • Thyroid storm is a life-threatening condition that is caused by sudden and severe worsening of symptoms. It is an uncommon reaction that can occur after an infection, injury, or physical trauma, such as surgery or childbirth. It can also occur in pregnancy if the person has undiagnosed or poorly controlled hyperthyroidism.
  • Hyperthyroidism has traditionally been associated with weight loss and being underweight.

The reason behind this is that hyperthyroidism can increase body metabolism and heat production and cause greater overall energy use, resulting in a tendency toward weight loss.

If you are experiencing any symptoms of a hormonal imbalance, or simply want to understand your hormone health, we’re here to get you the answers you deserve. The Hertility Health journey includes a tailored at-home hormone test, digital personalised results, access to highly-rated health experts, and clinics, educational content and a community of care. We’re here to support you throughout your journey, from the comfort of your couch.


Sarne D. Effects of the Environment, Chemicals and Drugs on Thyroid Function. [Updated 2016 Sep 27]. In: Feingold KR, Anawalt B, Boyce A, et al., editors. Endotext [Internet]. South Dartmouth (MA):, Inc.; 2000-. Available from: 

Bernadette Biondi, Leonard Wartofsky, Treatment With Thyroid Hormone, Endocrine Reviews, Volume 35, Issue 3, 1 June 2014, Pages 433–512, 

Shahid MA, Ashraf MA, Sharma S. Physiology, Thyroid Hormone. [Updated 2021 May 12]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Available from:  

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