Hypothyroidism/ Underactive Thyroid

What is Hypothyroidism?

Hypothyroidism is a common endocrine condition where the thyroid gland does not produce enough thyroid hormones to meet the body’s needs. These hormones, primarily thyroxine (T4), and triiodothyronine (T3), play a vital role in regulating metabolism, energy levels, heart function, body temperature, the reproductive system and brain development.

When hormone production drops, the body’s metabolic processes slow down, leading to a range of symptoms that can affect physical, cognitive, and emotional well-being. Although hypothyroidism is a long-term condition, it is easily remediable. With timely diagnosis, and proper treatment we can restore normal thyroid hormone levels, and improve quality of life.

What are the types of Hypothyroidism?

Hypothyroidism can be classified into several types based on its underlying causes, which are:

• Primary hypothyroidism – primary hypothyroidism is the most common form, resulting from a problem with the thyroid gland itself. It may be due to autoimmune disease, surgical removal, radiation or iodine deficiency.
• Secondary hypothyroidism – secondary hypothyroidism is caused by an insufficient stimulation of thyroid by the pituitary gland (the master endocrine gland), which produces thyroid-stimulating hormone (TSH). This is rare and often due to pituitary tumors.

• Tertiary hypothyroidism – tertiary hypothyroidism is an extreme of hypothyroidism that occurs when the hypothalamus fails to produce thyrotropin-releasing hormone (TRH), disrupting the thyroid hormone production cascade.

• Congenital hypothyroidism – congenital hypothyroidism is a condition present at birth, which may lead to developmental delays if not treated promptly.

• Subclinical hypothyroidism – in its early form, TSH levels are elevated, but the T3 and T4 remain within the normal ranges. It is benign till it reaches a more severe state.

What causes Hypothyroidism?

There are several factors that can lead to hypothyroidism, including:

• Autoimmune thyroiditis (Hashimoto’s disease) – the most common cause, where the immune system attacks the thyroid gland.

• Certain medications – drugs like lithium and amiodarone can interfere with thyroid function.

• Congenital thyroid disorders – in some cases, the thyroid gland may be underdeveloped or absent from birth. With neonatal screening, this is picked-up soon after childbirth.

• Iodine deficiency or excess – both low, and high iodine levels can affect thyroid hormone production. This is rare in Singapore. 

• Radioactive iodine therapy – used to treat hyperthyroidism, this therapy can result in underactive thyroid function.

• Radiation to the neck or head – often associated with cancer treatment, often head and neck cancers such as nasopharyngeal carcinoma

• Thyroid surgery – partial or total removal of the thyroid gland can reduce hormone production.

What are the symptoms of Hypothyroidism?

When it comes to hypothyroidism, symptoms often develop gradually, and can be easily overlooked. Be that as it may, some common signs include:

• Cold intolerance.
• Constipation.
• Depression or mood changes.
• Dry skin and brittle hair.
• Fatigue and low energy.
• Hoarseness.
• Menstrual irregularities or heavier periods.
• Memory problems or difficulty concentrating (brain fog).
• Muscle weakness or cramps.
• Puffy face or swelling in the neck.
• Slow heart rate.
• Weight gain despite unchanged appetite.

Dr. Dinesh finds fatigue, cold intolerance, weight gain and constipation the most common presenting symptoms for hypothyroidism. 

Who is at risk of Hypothyroidism in Singapore?

While hypothyroidism can affect anyone, certain groups are more susceptible due to biological, genetic or environmental factors. In Singapore, awareness of these risk groups is crucial for early detection, and intervention, especially since symptoms may be subtle or mistaken for other conditions.

Some individuals with higher risk of developing hypothyroidism include:

• Age – as people age, thyroid function may naturally decline. The thyroid becomes less efficient at producing hormones, and the immune system’s ability to regulate itself may decrease, increasing the risk of autoimmune thyroiditis causing hypothyroidism. Older adults may also have non-specific symptoms, such as fatigue or depression that may be put down to age-related causes rather than hypothyroidism.

• Gender – hypothyroidism is significantly more common in women than men, particularly those over 40 years old. This is due to hormonal differences, genetic variations and the unique characteristics of the female immune system. Women are therefore more prone to all autoimmune conditions including including Hashimoto’s thyroiditis (the most common cause of hypothyroidism).

• Family history – a family history of hypothyroidism, Hashimoto’s disease or other thyroid disorders raises the likelihood of developing the condition. As genetics play a strong role in immune system regulation, meaning those with affected relatives may inherit a predisposition to autoimmune thyroid dysfunction.

• Autoimmune conditions – individuals with autoimmune diseases, such as type 1 diabetes, coeliac disease or systemic lupus erythematosus (SLE), are more likely to develop hypothyroidism. This is because autoimmune disorders tend to cluster and having one autoimmune condition increases your chance of having another. There are also genetic conditions that can cause multiple endocrine autoimmune diseases in the single individual. 

• Postpartum women – after childbirth, some women may experience postpartum thyroiditis, an inflammation of the thyroid gland triggered by immune system changes. This condition may initially cause hyperthyroidism, followed by a period of hypothyroidism. While it often resolves, some women develop permanent hypothyroidism after pregnancy.

• Previous hyperthyroidism treatment – individuals who have undergone treatment for an overactive thyroid, especially radioactive iodine therapy or thyroid surgery, are at risk of developing hypothyroidism. These treatments intentionally reduce thyroid activity, and for some, the gland becomes underactive permanently, requiring lifelong hormone replacement.

• Radiation exposure or iodine imbalance – exposure to radiation, especially in the neck or chest area during medical treatment, can damage thyroid cells, and impair hormone production. In addition, both excessive, and insufficient iodine intake can disrupt thyroid hormone synthesis. While iodine deficiency is rare in Singapore due to iodised salt, those consuming extreme diets or supplements should be cautious.

What are the complications associated with Hypothyroidism?

It is important to promptly, and effectively treat hypothyroidism. This is because untreated or poorly managed hypothyroidism can lead to serious health complications, such as:

• Depression and cognitive decline – low thyroid hormone levels affect brain function, and mood regulation. This can lead to symptoms such as low mood, memory difficulties, slowed thinking, and lack of concentration. Older adults, in particular, may experience more pronounced cognitive decline that mimics dementia. This is termed pseudodementia. Dr Dinesh comments that thyroid function is an important test in ruling this out in those with cognitive decline. 

• Goitre – an enlarged thyroid gland caused by overstimulation from TSH. As the gland tries to compensate for low hormone levels, it may grow in size, sometimes leading to visible neck swelling, trouble swallowing or discomfort.

• Heart problems – hypothyroidism can raise levels of low-density lipoprotein (LDL) cholesterol, slow down the heart rate (bradycardia), and may increase the risk of high blood pressure, and heart disease over time.

• Infertility – low thyroid hormone levels can interfere with ovulation, and menstrual regularity, making it more difficult to conceive. In men, it may also affect sperm quality.

• Myxoedema – a rare but severe form of hypothyroidism, myxoedema is a medical emergency. It presents with extreme drowsiness, confusion, low body temperature, and can progress to coma if not treated promptly and has a high mortality.

• Pregnancy complications – untreated hypothyroidism during pregnancy increases the risk of miscarriage, pre-eclampsia (high blood pressure), premature birth, and impaired brain development in the baby.

How is Hypothyroidism diagnosed?

Diagnosing hypothyroidism involves a combination of symptom assessment, medical history, and blood tests to evaluate thyroid function. Due to the fact that symptoms can be subtle or overlap with other conditions, a proper diagnosis requires laboratory confirmation.

The key tests used include Thyroid Function Tests (TFTs), such as:

TEST	PURPOSE	WHAT IT TELLS US
Thyroid Stimulating Hormone (TSH)	First-line test for thyroid function.	TSH is typically raised when hypothyroidism is present. This occurs because the pituitary gland increases TSH production to stimulate the underactive thyroid gland.
Free T4 (Thyroxine)	Confirms the diagnosis.	Free T4 levels are usually low in overt hypothyroidism. A low T4 alongside a high TSH confirms the diagnosis.
Free T3 (Triiodothyronine)	May be checked in certain cases.	T3 may be normal or slightly low in early hypothyroidism, but is more relevant in hyperthyroidism diagnosis.
Anti-thyroid antibodies	Identifies autoimmune thyroid disease.	The presence of antibodies, such as anti-TPO or anti-Tg, suggests Hashimoto’s thyroiditis.

How is Hypothyroidism treated?

Treating hypothyroidism fundamentally involves personalised thyroid hormone replacement with active monitoring to fine-tune doses. This remedies symptoms and restores normal metabolism thus increasing quality of life. At The Metabolic Clinic, our doctors take a personalised approach to outlining a treatment plan that can help patients lead full, and healthy lives with the right support.

Generally, treatment involves:

TREATMENT	HOW IT WORKS	NOTES
Levothyroxine (T4)	Synthetic version of thyroxine (T4), the hormone your thyroid naturally produces.	Taken as a once-daily oral tablet. The dose is carefully adjusted based on age, weight, underlying health conditions, and blood test results.
Combination therapy (T4 + T3)	Occasionally considered for those who do not feel better on T4 alone.	Not routinely recommended as scientific literature has failed to show benefit, but may benefit a small group of patients under specialist guidance.

Additionally, our doctors will complement treatment with the following lifestyle modifications, and monitoring:

• Avoid certain supplements or medications near dosing – iron, calcium, soy, and some medications can interfere with levothyroxine absorption. As such, it is best to leave a 2-hour gap where possible.

• Consistent medication timing – Levothyroxine should be taken on an empty stomach, ideally in the morning, 30 minutes prior to food, to ensure optimal absorption.

• Monitoring symptoms – Monitoring for resolution of fatigue, weight changes, cold intolerance or mood changes.

• Regular blood tests – TSH, and Free T4 are monitored every 4 to 8 weeks when starting or changing dosage, then every 6 to 12 months once stable.

Summary

Hypothyroidism is a common yet often overlooked condition that can affect your energy, mood, metabolism, and overall well-being. The good news is that with timely diagnosis, and appropriate treatment, it is highly manageable. As a result, allowing most individuals to regain control of their health, and live full, active lives.

If you are experiencing symptoms or fall into a higher-risk group, book a consultation with our experienced team today for a thorough thyroid assessment, and personalised care plan tailored to your needs.

Frequently Asked Questions