IMPAIRED T4 to T3 CONVERSION

T4 to T3 conversion can be impaired by a variety of physiological stressors, including chronic stress, calorie restriction, insulin resistance, chronic illness, liver dysfunction, inflammation, and cortisol imbalances. Nutrient deficiencies—particularly in selenium, zinc, iron, and key vitamins—as well as gut dysfunction, certain medications, toxin exposure, and underlying infections can also interfere with this conversion process. In some cases, genetic factors or prolonged physiological stress can further reduce the body’s ability to properly convert T4 into active T3.

If your RT3 is clearly low in the range, it’s often not a problem. But when it starts creeping up, you might be confused about if your result means you have a Reverse T3 issue. In those cases, calculating the Free T3 (or Total T3) to Reverse T3 ratio gives you a much clearer picture—and it’s something I always check.