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What is free T4?

T4, or thyroxine, is one of the two main thyroid hormones in the human body. Once released into the bloodstream, TSH is responsible for stimulating the thyroid gland to produce hormones T4 and T3. T4 is inactive and is converted to the active T3 form mainly in the liver, but also in the kidneys, brain, and other organs [1]. While bound T4 (attached to proteins) is unable to enter the body’s tissues, free T4 is able to enter tissues more readily.

Why is free T4 important?

Tracking your free T4 levels allows you to understand the health of your thyroid gland, which is an integral part of your endocrine system. Free T4 tests may also provide more accurate information than a total T4 test and are therefore used more frequently. Thyroid hormones are vital to metabolism, heart and digestive functions, muscle control, brain development, and bone maintenance, among other roles.

High free T4 may be indicative of thyrotoxicosis which can result from hyperthyroidism (overactive thyroid gland) or thyroid gland inflammation (thyroiditis). Low free T4 may point to hypothyroidism (underactive thyroid gland) which can be caused by autoimmune diseases, inadequate iodine intake, or certain medications. Symptoms of hyperthyroidism may include weight loss, rapid or irregular heartbeat, and increased bowel movements among other issues [2]. Symptoms of hypothyroidism on the other hand may include fatigue, weight gain, sensitivity to cold, low heart rate, and other physical and mental issues [3]. If you are concerned with your levels, it is important to consult with your physician.

How can I better understand my free T4 levels?

To better understand your free T4 levels, you can use the following reference ranges:

  • Out of range: 0-0.59 ng/dL
  • In range: 0.59-1.1 ng/dL
  • Optimal: 1.1-1.22 ng/dL
  • Out of range: 1.22 ng/dL

Free T4 test results are analyzed in conjunction with other thyroid tests to determine whether the thyroid gland is functioning properly.

While other thyroid hormones like T3 and TSH can fluctuate throughout the day, T4 remains relatively stable for each person.

How can I maintain optimal free T4 levels?

If you need to maintain or adjust your free T4 levels, consider the following strategies:

Dietary Changes: Consuming less iodine and eating more cruciferous veggies can help to lower high free T4 levels [4]. On the other hand, obtaining adequate iodine and vitamin B2 intake and increasing protein intake, specifically of the amino acids valine, arginine, and leucine can help to increase low T4 levels [5].

Lifestyle Changes: Abstaining from alcohol can help increase free T4 levels [6].

Where can I learn more?

DISCLAIMER: IF YOU ARE CONCERNED WITH ANY OF YOUR RESULTS, PLEASE CONSULT WITH YOUR PHYSICIAN.

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