Signs and causes of an underactive thyroid

An underactive thyroid (also known as hypothyroidism) is more common than many people realise, especially in women, yet it often goes unnoticed. As the symptoms can be subtle at first, like low energy, weight changes or feeling unusually cold, it’s easy to put them down to everyday life. But over time, these small changes can start to add up.

The thyroid is a small, butterfly-shaped gland located at the base of your neck.² It forms part of the endocrine system, which is responsible for producing hormones that regulate many of our body’s functions.³ One of the thyroid’s main roles is to support metabolism, which is how your body converts food into energy. It does this by producing two key hormones called thyroxine (T4) and triiodothyronine (T3).¹ These hormones influence energy levels, body temperature, heart rate and how efficiently your body uses nutrients.¹

An underactive thyroid happens when the thyroid gland doesn’t produce enough T3 and T4 hormones, which can cause many of the body’s processes to slow down.⁴ It’s estimated that around 2% of people in the UK are affected, with women making up the majority of that percentage.³

Symptoms of an underactive thyroid can vary from person to person and often develop slowly over time. Common signs of an underactive thyroid include:⁵

If you’re experiencing persistent or multiple symptoms, particularly fatigue, weight changes or irregular periods, it’s important to speak to your GP. A healthcare professional can assess your symptoms and if appropriate, arrange tests to check your thyroid function.

There are several possible causes of an underactive thyroid but the most common include:^4,10

An underactive thyroid is typically assessed through a blood test.⁴ This test measures levels of thyroid-stimulating hormone and thyroid hormones, helping healthcare professionals determine whether the thyroid is functioning as expected.⁴

While an underactive thyroid requires medical assessment, general lifestyle habits can play a role in supporting overall health and how you feel day to day. For example, getting enough sleep, managing stress and eating a balanced diet can help support energy levels, mood and metabolic health, all of which may be affected when thyroid function is low.^6,7,8,9 However, these approaches aren’t a substitute for medical care, so if you suspect a thyroid issue, it’s important to speak to your GP.

An underactive thyroid can quietly influence everything from your energy levels to how your body manages weight, often in ways that aren’t immediately obvious. As the symptoms can be subtle and overlap with other conditions, it’s important not to jump to conclusions or self-diagnose.

Disclaimer – This article provides informational advice and is not a substitute for medical care. Working with experts for accuracy, we take great care to ensure the information is up-to-date and relevant. However, you should always consult your GP or healthcare professional before using supplements or alternative products, particularly if you have medical conditions or are under supervision.