Thyroid Hormone Conversion

In hypothyroidism, bile salt supplementation may be beneficial because sluggish bile production could contribute to poor T4-to-T3 conversion. Bile salts facilitate 80% of T4-to-T3 thyroid hormone conversion, primarily in the liver. T4 is the inactive storage form of thyroid hormone and T3 is the active form that drives metabolism. The thyroid produces mostly T4, while T3 is the more active thyroid hormone. T4 must be converted largely by the liver into active thyroid hormone forms. Gut bacteria can activate an inactive T3 form and increase active hormone availability. In hyperthyroidism, bile salt supplementation is contraindicated because it further increases T4-to-T3 conversion and amplifies the already-excessive hormonal state. Damaged gut flora may leave as much as 20% of potential thyroid activity unavailable.