Free Triiodothyronine Has a Distinct Circadian Rhythm That Is Delayed but Parallels Thyrotropin Levels

Abstract

FT3 shows a circadian rhythm with a periodicity that lags behind TSH, suggesting that the periodic rhythm of FT3 is due to the proportion of T(3) derived from the thyroid. Optimizing thyroid hormone replacement may need to take these rhythms into account.