The thyroid may be a small gland, but it has an important role in keeping the body's systems functioning normally. Located at the front of the neck, the thyroid produces hormones that help regulate metabolism and influence how quickly many processes in the body take place.

The main hormones produced by the thyroid are thyroxine, known as T4, and triiodothyronine, known as T3. T4 is produced in larger quantities and can be converted into T3 in different tissues throughout the body. T3 is the more active thyroid hormone and plays an important role in regulating the body's energy use.

The thyroid does not work independently. Its activity is controlled through a communication system involving the hypothalamus and pituitary gland in the brain. The pituitary produces thyroid stimulating hormone, or TSH, which signals the thyroid to produce thyroid hormones. This feedback system helps maintain appropriate hormone levels.

When the thyroid produces too little hormone, a condition called hypothyroidism can develop. When it produces too much, this is known as hyperthyroidism. Both conditions can affect how the body functions and can cause a range of symptoms.

Thyroid disorders can have different causes. For example, autoimmune conditions can affect thyroid function, while other thyroid problems may be related to inflammation, certain medications, thyroid nodules or previous treatment involving the thyroid. The appropriate diagnosis therefore depends on the individual and cannot be determined from symptoms alone.

Because thyroid hormones influence metabolism and multiple body systems, thyroid problems can sometimes have effects that appear unrelated to the neck. Changes in energy, heart rate, temperature tolerance, digestion, concentration and mood can all occur in some thyroid disorders.

For example, with both T3 and T4 medication, you are likely to experience a loll in energy in the afternoon. Flare ups and other symptoms remain  common. 
The British Thyroid Foundation offers accessible information about how the thyroid works, thyroid conditions, testing and treatment. Its educational resources can help people understand the terminology they may encounter and provide reliable information to support conversations with their healthcare team.

Learning the basics of thyroid function can make medical information and test results easier to follow. However, thyroid health is highly individual. If you have persistent symptoms or concerns about your thyroid, discussing them with a qualified healthcare professional is the best way to determine whether further assessment or testing is appropriate.

For further information about thyroid function and thyroid conditions, explore the patient resources available from the British Thyroid Foundation and elsewhere.

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