What causes an underactive thyroid (hypothyroidism)?

In this article, we will be exploring a condition known as hyperthyroidism, also known as an underactive thyroid. We'll be answering key questions like what is the difference between an underactive thyroid and hyperthyroidism? How do doctors check for it? And, importantly, what are the causes?

Key Takeaways

Causes of an Underactive Thyroid:

An underactive thyroid (hypothyroidism) can be caused by the immune system attacking the thyroid (such as in Hashimoto's disease), previous thyroid treatments, iodine deficiency (rare in the UK), congenital hypothyroidism in babies, pituitary gland issues, and certain medications like lithium.

Immune System and Thyroid:

The immune system can cause an underactive thyroid through autoimmune disorders like Hashimoto's disease. In this condition, the immune system makes antibodies that attack the thyroid, leading to damage and reduced hormone production.

Treatment for an Underactive Thyroid:

Hypothyroidism can be effectively treated with thyroid hormone medicine. When taken as prescribed, this medication can control the condition, allowing individuals to manage their symptoms and maintain proper thyroid function.

Context

What is an underactive thyroid?

According to the NHS, an underactive thyroid, or hypothyroidism, occurs when the thyroid gland fails to produce sufficient thyroxine, commonly known as T4. This hormone plays a crucial role in regulating various bodily functions, and a shortage of it can lead to a range of health issues. When your thyroid gland is not properly conducting your bodily function, it can lead to a number of different problems.

Is hyperthyroidism the same as an underactive thyroid?

No, hyperthyroidism and hypothyroidism are not the same. While hypothyroidism, or an underactive thyroid, arises when the thyroid gland doesn't produce enough thyroxine for the body's requirements, hyperthyroidism is the opposite. In hyperthyroidism, according to the British Thyroid Foundation, the thyroid gland produces an excess of thyroxine, leading to an accelerated metabolism and a different set of health challenges.

How can hyperthyroidism be checked?

According to the NHS, to check for hyperthyroidism, your GP may schedule a thyroid function test, a blood test that assesses the levels of crucial thyroid hormones. This includes checking the thyroid-stimulating hormone (TSH) produced by the pituitary gland, which regulates thyroid hormone production. Additionally, the levels of triiodothyronine (T3) and thyroxine (T4), two main thyroid hormones, are examined. This comprehensive evaluation helps the medical team gauge the thyroid's performance and identify any abnormalities in hormone levels, aiding in the diagnosis of hyperthyroidism.

Causes Of An Underactive Thyroid

What causes an underactive thyroid (hypothyroidism)?

According to the NHS, an underactive thyroid results from the immune system attacking the thyroid (Hashimoto's disease being a common trigger) or previous thyroid treatments. Other causes include iodine deficiency (though rare in the UK), congenital hypothyroidism in babies, pituitary gland issues, and certain medications like lithium and interferons.

Can your immune system cause an underactive thyroid?

Yes, your immune system can cause an underactive thyroid, according to the National Institute of Diabetes and Digestive and Kidney Diseases. In Hashimoto's disease, an autoimmune disorder, the immune system makes antibodies that attack the thyroid. This leads to a build-up of white blood cells in the thyroid, damaging it and preventing it from making enough thyroid hormones, resulting in an underactive thyroid.

Can having had previous thyroid treatment cause an underactive thyroid?

Yes, having had previous thyroid treatment can indeed lead to an underactive thyroid. For instance, if you've undergone radioactive iodine treatment, often used for hyperthyroidism, it gradually destroys thyroid cells and may eventually result in hypothyroidism. Additionally, individuals receiving external radiation therapy for head or neck cancers might experience thyroid damage if the thyroid is within the treatment area. This is based on information gathered by the National Institute of Diabetes and Digestive and Kidney Diseases.

Can a lack of dietary iodine cause an underactive thyroid?

Yes, a lack of dietary iodine can indeed cause an underactive thyroid. Severe iodine deficiency leads to conditions like goitre and hypothyroidism (Eastman & Zimmerman, 2018). Even when the thyroid tries to compensate by increasing activity to maximise iodine uptake and recycling, the concentrations remain too low to enable adequate production of thyroid hormones. Therefore, insufficient dietary iodine can directly impact the thyroid's ability to generate the necessary hormones, resulting in an underactive thyroid. 

Treatments

Can an underactive thyroid be treated?

An underactive thyroid, or hypothyroidism, can often be effectively treated. The primary approach involves thyroid hormone medicine, which, when taken as prescribed, can effectively control the condition. It's crucial to adhere to the recommended dosage and not discontinue the medication without consulting your doctor. According to the National Institute of Diabetes and Digestive and Kidney Diseases, consistent and proper use of thyroid hormone medicine can typically bring hypothyroidism under control, allowing individuals to manage their condition and maintain optimal thyroid function.

Is hypothyroid treatment available online?

Yes, you can buy treatments for an underactive thyroid online from EU Meds. At EU Meds, you can purchase a number of popular hypothyroid treatments, including levothyroxine and liothyronine. It is easy to purchase your medication online. Simply select the amount of medication that you need, complete our free online consultation that will provide you with our free private prescription upon acceptance, and then complete your purchase. Please note, all requests for supply of prescription medications are subject to an online clinical consultation and the decision to prescribe will be made by a registered doctor. 

Do I need a prescription for hypothyroid medication?

Yes, hypothyroid medication typically requires a prescription. Drugs commonly prescribed for hypothyroidism, such as levothyroxine and eltroxin, are not available over the counter.

Medically Reviewed by:
Dr. Irfan Siddique MBBS
GMC reference no: 7694522
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Sources

• NHS - Underactive Thyroid Causes

• NHS Inform - Underactive Thyroid Causes

• Mayo Clinic - Hypothyroidism Causes

• BTF - What Is Thyroid Disorder