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Free Thyroxine Index (FTI) is a measure of thyroid function. It is the product of the level of thyroid hormone thyroxine (T4) and the uptake of triiodothyronine (T3). This measure takes into account not only the absolute level of hormones in the blood, but also the binding capacity of proteins that attach to those hormones. (source)
Low serum FTI levels can be influenced by physiological factors affecting the production and regulation of hormones by the thyroid gland, as well as nutritional factors crucial for thyroid function. Essential nutrients like iodine, selenium, and zinc are vital for proper thyroid hormone synthesis, while factors such as stress and inadequate sleep can disrupt thyroid function. (source, source)
Prioritize iodine-rich foods: Iodine is an essential component of thyroid gland hormone synthesis. (source) Iodine supports cellular pathways that lead to the production of thyroid hormones, T3 and T4, which increases FTI. (source) 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)
Maintain an athletic body composition: Free thyroxine has been shown to be associated with body fat percentage. (source) Changes in body mass are associated with changes in energy metabolism requirements. These changes influence concentrations of thyroid hormones which regulate energy expenditure and appetite. (source) Maintaining an athletic body composition will help regulate thyroid hormone levels and FTI. Recommendation: Maintain a high-performance diet and exercise program that supports a body composition of no more than 15% body fat for men and 20% for women.
Supplement with iodine: Iodine is an essential component of thyroid gland hormone synthesis. (source) Iodine supports cellular pathways that lead to the production of thyroid hormones, T3 and T4, which increases FTI. (source) Recommendation: Supplement with at least 75 mcg of iodine daily.
Elevated serum FTI levels can stem from physiological factors related to thyroid function and metabolism, as the thyroid gland plays a key role in hormone production. Nutritionally, factors like iodine intake and overall metabolic health can also influence thyroid hormone levels. (source, source)
Limit foods high in iodine: Iodine is an essential component of thyroid gland hormone synthesis. (source) Iodine supports cellular pathways that lead to the production of thyroid hormones, T3 and T4, which increases FTI. (source) Limiting the intake of iodine will decrease FTI. Recommendation: Monitor and limit excess consumption of foods high in iodine, like fish, dairy, and seaweed.
Maintain an athletic body composition: Free thyroxine has been associated with body fat percentage. (source) Changes in body mass are associated with changes in energy metabolism requirements. These changes influence concentrations of thyroid hormones which regulate energy expenditure and appetite. (source) Maintaining an athletic body composition will help regulate thyroid hormone levels and FTI. Recommendation: Maintain a high-performance diet and exercise program that supports a body composition of no more than 15% body fat for men and 20% for women.
Avoid iodine: Iodine is an essential component of thyroid gland hormone synthesis. (source) Iodine supports cellular pathways that lead to the production of thyroid hormones, T3 and T4, which increases FTI. (source) Limiting the intake of iodine will decrease FTI. Recommendation: Monitor excess iodine intake and iodine concentrations in supplements.
Supplement with L-carnitine: Supplementing with L-carnitine has been shown to help improve thyroid function. (source) Research suggests that L-carnitine inhibits the uptake and action of thyroid hormones, thereby decreasing FTI. (source) Recommendation: Supplement with at least 2 g of L-carnitine.
