Reverse T3 (rT3)

Specialist

also —

What it isReverse T3 is an inactive metabolite produced when peripheral tissues remove the wrong iodine atom from T4. The body uses this alternate pathway to ramp down thyroid hormone activity during stress, fasting, or illness.

DoesFunctions as a brake on metabolic activity by competing with active T3 at receptors.

GoodLow rT3 signals that the body isn't redirecting T4 into the inactive pathway.

BadElevated rT3 — especially with low Free T3 — defines "low T3 syndrome" and tracks chronic stress, illness, low-calorie states, overtraining, and inflammation.

Standard

8–25 ng/dL.

Optimal

8–14 ng/dL (lower is good)

Modifiers

Rises with caloric restriction, illness, stress, cortisol; falls with adequate nutrition and rest.

How to optimize

Lifestyle: Avoid extreme caloric restriction; adequate sleep; stress management; recovery from overtraining.
Diet: Adequate calories and carbohydrates; iron, selenium, zinc; avoid very long fasts in chronic-stress states.
Supplements: Selenium (200µg/day), zinc (15–30mg/day), iron if deficient.
Peptides: —
Drugs: Liothyronine (T3) in selected patients with persistent low T3 syndrome.

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