Thyroid Hormone - Everything You Need To Know

“I have started to gain more weight” 

“I feel more tired than usual”

“I’m having dry and coarse hair”

Are you experiencing any of these symptoms? 

Do you know what causes these?

It’s the little butterfly-shaped thyroid gland located in your neck, which could be causing you trouble. The thyroid hormones produced by the thyroid gland support nearly every cell in your body.¹ Let’s understand how!

Overview Of The Thyroid Hormone

The thyroid gland looks after the formation and secretion of thyroid hormones. These hormones are crucial for the development and differentiation (to mature and perform a specific function) of our body cells.^1,2

What Are The Functions Of Thyroid Hormones?

Thyroid hormones play an important part in regulating the Basal Metabolic Rate (BMR) i.e. the number of calories needed to keep our body functioning at rest. These hormones can also:³

• Regulate carbohydrate, protein, and fat metabolism
• Maintain electrolyte balance
• Control body temperature
• Support the process of RBC formation
• Deposit calcium and phosphate in bone

Hormones Produced By The Thyroid Gland

The thyroid gland produces 90% inactive thyroid hormone or thyroxine (T4) and only 10% active thyroid hormone or triiodothyronine (T3). Both T3 and T4 levels are regulated by the Thyroid-Stimulating hormone (TSH) and they help increase the basal metabolic rate to make the body cells work harder. And, this can have the following effects on our body:^4,5,6

• Raise in body temperature
• Faster heartbeat
• Brain maturation in children
• Growth promotion in children

But, do you know what exactly triggers the thyroid gland to produce T3 and T4?

It is a network called Hypothalamic-Pituitary-Thyroid (HPT) that plays a role here and decides a defined point for the production of thyroid hormones. This network include:⁶

• Thyrotropin-Releasing Hormone (TRH) from the hypothalamus i.e. a part of your brain 
• Thyroid-Stimulating Hormone (TSH) from the pituitary gland i.e. a small gland at the base of your brain
• Thyroxine or tetraiodothyronine (T4)

Apart from T3 and T4, calcitonin is the third hormone produced by the thyroid gland and is majorly involved in calcium and bone metabolism.⁵

How Does The Hypothalamic-Pituitary-Thyroid (HPT) Network Work?

Hypothalamus releases Thyrotropin-Releasing Hormone (TRH), which, in turn, stimulates the pituitary gland to release Thyroid-Stimulating hormone (TSH). TSH is then triggered to release Thyroxine or tetraiodothyronine (T4) and triiodothyronine (T3). This process takes place in a loop and helps maintains a constant level of thyroid hormones in the body.^6,7

• Once the T4 and T3 levels increase, the TRH and TSH production is shut off and
• When the T4 and T3 levels drop, the TRH and TSH production starts again^6,7

So, everything seems fine as far as there is a hormonal balance, 

But what happens when there is a hormonal imbalance? 

Let’s see…

What Happens When There Is Thyroid Hormone Imbalance?

A hormonal imbalance can result in an overactive thyroid (hyperthyroidism) or an underactive thyroid gland (hypothyroidism) which may cause the following symptoms:

• Symptoms of hyperthyroidism: Heat intolerance, weak muscles, diarrhoea, nervousness, irritability, weight loss, trouble sleeping, irregular or rapid heartbeat, tremors, and goiter (enlargement of thyroid gland).^8,9
• Symptoms of hypothyroidism: Fatigue, weight gain, cold intolerance, depression, constipation, dry skin, hair thinning, muscle and joint pain, menstrual irregularities, and infertility issues.^10,11

Recommended Tests To Check Hormonal Imbalance

Thyroid Function Test (TFT) measures the thyroid gland’s ability to produce and regulate its hormone production. TFTs diagnose thyroid gland disorders and they include:¹²

Thyroid-Stimulating Hormone (TSH) Test

Measuring the TSH level is an excellent way to assess thyroid function. TSH is made in the pituitary gland and notifies the thyroid how much T4 and T3 to produce. In hypothyroidism, the thyroid gland does not make enough hormones (T4 and T3), so the TSH level is high. While in hyperthyroidism, the thyroid gland produces too many hormones (T4 and T3) causing a low TSH level.¹³

Free Thyroxine (FT4) Test 

A total T4 (main form of thyroid hormone) test measures the bound T4 as well as the free T4 together. Bound T4 is attached to the proteins and is not able to enter body tissues. But, as the free T4 isn’t bound, it can circulate easily in the body tissues. So, as the free T4 levels are not affected experts prefer to assess FT4 to diagnose hormonal imbalances. ^7,13

Triiodothyronine (T3) Test 

Similar to T4, a total T3 test measures the bound T3 as well as the free T3 together. Bound T3 is attached to the proteins and free T3 isn’t. Elevated T3 level is usually seen in hyperthyroid patients. At times, when the T4 levels are normal, T3 can still be high. Hence, to diagnose the severity of hyperthyroidism T4 and T3 tests are helpful.^7,13,14

Thyroid Antibodies 

When the body’s immune system attacks thyroid, the concentration of thyroid antibodies such as anti-thyroid peroxidase (anti-TPO) and anti-thyroglobulin (anti-TG) increases. This is usually seen in Hashimoto’s (when the immune system attacks the thyroid) or Graves’ (an immune system disorder which leads to overproduction of thyroid hormones) disease.^15,16

Calcitonin 

Calcitonin plays an important role in calcium and bone metabolism. A rise in calcitonin levels is seen in certain types of thyroid cancer, but can also be a sign of kidney failure.¹⁶ 

The Connection Between Thyroid And Fertility Revealed

Thyroid disease is quite common in women and can lead to infertility or miscarriages.¹⁷

In recent years, the incidence of thyroid cancer has increased worldwide and is commonly seen in women aged between 20 to 39 years.¹⁸ And, if thyroid disorders are not treated or diagnosed on time, they may lead to infertility.¹⁷ Here’s how:

Hypothyroidism or hyperthyroidism can cause menstrual irregularities or anovulatory cycles (when an egg doesn’t release from the ovary during menstruation) in women. Also, if you’re pregnant and these disorders aren’t treated in time they can increase the risk of miscarriage and premature birth. ^17,19,20

However, a normal thyroid function is essential to maintain a pregnancy and for optimal fertility in women.¹⁷ Furthermore, keeping your hormonal health under check can be useful especially if you’re:

• actively trying to conceive, 
• experiencing certain symptoms (heat or cold intolerance, weight gain or loss, and constipation or diarrhea), and
• planning for parenthood in the near future!

Where Can You Get Your Thyroid Hormone Levels Checked?

To detect any thyroid abnormality, the initial tests of choice are TSH and free thyroxine (FT4) tests.4 So, if you wish to get your thyroid levels checked, get in touch with any nearby clinic.