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T4, or thyroxine, is the main hormone secreted by the thyroid gland. Thyroid hormones are responsible for a range of bodily functions, including metabolism and growth. The amount of T4 produced is controlled by TSH (thyroid-stimulating hormone), and total T4 is a measure of the amount of thyroxine that is both bound and unbound to proteins in the blood (source).
Low total T4 levels can stem from physiological factors related to thyroid function, as the thyroid gland produces T4. Nutritionally, insufficient intake of iodine can contribute to decreased T4 levels. (source, source)
Prioritize iodine-rich foods: Iodine is essential for the production of T4. (source) T4 is composed of four iodine atoms, thus making iodine a crucial factor for the synthesis of T4. (source) Consuming iodine increases total T4. Recommendation: Consume at least one serving of foods high in iodine daily.
One serving examples: Greek Yogurt (1 cup), Seaweed (dried) (3 g), Cod (3 oz), Scallops (3 oz)
Train regularly: Exercise has been shown to increase serum T4. (source) Exercise activates the sympathetic nervous system, which stimulates the secretion of thyroid hormones, including T4, thus increasing levels in the blood. (source) Recommendation: Follow a structured training program that exerts your body through multiple resistance and aerobic intensities. This includes a structured aerobic program that ensures at least 150 minutes of moderate intensity (50 to 70% max heart rate) or 75 minutes of high intensity (75% max heart rate or greater) a week and a structured resistance training program with moderate to heavy loads at least twice a week for resistance training. The final set of each resistance training exercise should be taken within two repetitions of failure.
Supplement with iodine: Iodine is essential for the production of T4. (source) T4 is composed of four iodine atoms, thus making iodine a crucial factor for the synthesis of T4. (source) Supplementing with iodine increases total T4. Recommendation: Supplement with at least 75 mcg of iodine daily.
Elevated total T4 levels can often stem from physiological factors affecting the production and metabolism of thyroid gland hormones. Nutritionally, dietary levels of iodine and selenium can affect T4 levels. (source, source, source)
Limit foods high in iodine: Iodine is essential for the production of T4. (source) T4 is composed of four iodine atoms, thus making iodine a crucial factor for the synthesis of T4. (source) Limiting the consumption of iodine decreases total T4. Recommendation: Monitor and limit excess consumption of foods high in iodine, like fish, dairy, and seaweed.
Supplement with selenium: T4 levels are inversely associated with selenium intake. (source) Selenium is an essential component of compounds that convert T4 to T3. (source, source) Supplementing with selenium reduces total T4 concentrations. Recommendation: Supplement with at least 50 mcg of selenium.
