Free Tri-iodothyronine (FT3)

What it is

Free tri-iodothyronine, often shortened to FT3, is a hormone produced by your thyroid gland, a small butterfly-shaped gland located at the front of your neck. Your thyroid gland makes two main hormones: thyroxine (T4) and tri-iodothyronine (T3). While T4 is the more abundant hormone, T3 is considered the more potent and active form.

Think of it like this: T4 is like a raw ingredient, and your body converts most of it into T3, which is the form that your cells can readily use to carry out their functions. FT3 refers to the amount of T3 that is not bound to proteins in your blood, meaning it's free and available to be used by your body's tissues.

The normal range for FT3 in the UK is typically between 3.1 and 6.8 picomoles per litre (pmol/l). This can vary slightly between different laboratories.

Why it matters

FT3 plays a crucial role in regulating your body's metabolism – essentially how your body uses energy. It influences many bodily functions, including:

• Heart rate: FT3 helps control how fast your heart beats.
• Body temperature: It contributes to maintaining your internal temperature.
• Digestion: It affects how quickly food moves through your digestive system.
• Energy levels: It impacts how energetic you feel.
• Brain function: It's important for cognitive processes and mood.
• Bone health: It plays a part in bone turnover.

Because FT3 is so central to metabolism, its levels can affect how you feel and function in many ways. When FT3 levels are too high or too low, it can lead to a range of symptoms.

What can cause it to be high or low

High FT3 levels can be associated with an overactive thyroid gland, a condition known as hyperthyroidism. In this situation, the thyroid produces too much thyroid hormone. This can sometimes happen due to conditions like Graves' disease or nodules on the thyroid gland. In rare cases, high FT3 might be seen temporarily if someone is taking too much thyroid hormone medication.

Low FT3 levels can be associated with an underactive thyroid gland, or hypothyroidism. Here, the thyroid doesn't produce enough thyroid hormone. This can occur due to autoimmune conditions like Hashimoto's thyroiditis, where the body's immune system mistakenly attacks the thyroid gland. Low FT3 can also be seen in people who are very unwell with non-thyroidal illnesses, as the body may reduce its conversion of T4 to T3 to conserve energy. Other factors that can be associated with lower FT3 levels include certain medications, severe illness, and nutritional deficiencies.

It's important to remember that FT3 levels are often interpreted alongside other thyroid hormone tests, such as TSH (Thyroid Stimulating Hormone) and FT4 (Free Thyroxine), to get a complete picture of thyroid function.

Lifestyle factors that may help

Maintaining a healthy lifestyle can support overall thyroid health and potentially influence hormone balance. Discussing these with your GP might be helpful:

• Balanced Diet: Ensuring your diet includes a variety of nutrients is important. Iodine, selenium, and zinc are minerals that play a role in thyroid hormone production and conversion. Foods like fish, nuts, seeds, and dairy products can be good sources.
• Stress Management: Chronic stress can affect hormone levels. Exploring techniques like mindfulness, meditation, yoga, or spending time in nature might be beneficial.
• Regular Exercise: Moderate, regular physical activity can support overall well-being and metabolism.
• Adequate Sleep: Getting enough quality sleep is vital for hormone regulation and overall health.

Questions to discuss with your GP

If you have concerns about your thyroid health or your FT3 levels, having a conversation with your GP is the best next step. Here are some questions you might consider discussing:

• What do my FT3 levels mean in the context of my overall health and other test results?
• Are there any specific lifestyle changes you would recommend for me based on my thyroid results?
• Could any of my current medications or supplements be affecting my FT3 levels?
• What are the potential causes for my FT3 levels being outside the normal range?
• What are the next steps in managing my thyroid health?