Normal thyroid results but still exhausted? Understanding reverse T3 and "cellular hypothyroidism"
You're tired all the time. You feel cold when everyone else is comfortable. Your thinking is foggy, your hair is thinning, and the number on the scale won't budge. You've had your thyroid checked, and you were told everything looks normal.
As a clinical naturopath, this is one of the most common stories I hear. Let's unpack one piece of the puzzle that often gets overlooked: reverse T3.
Thyroid hormones: the basics
Your thyroid gland mostly produces T4, which is essentially a storage hormone. It doesn't do much on its own. Your body converts it into one of two things:
T3 (active T3): the "accelerator" It enters your cells and tells them to produce energy.
Reverse T3 (rT3): a mirror-image version that fits the same receptors but doesn't switch them on. Think of it as the "brake"
Making some rT3 is completely normal. It's one of the ways your body fine-tunes how much energy you're using.
What does high reverse T3 mean?
When your body is under pressure, it can shift more T4 toward rT3 and less toward T3. Common triggers include:
Illness or infection, or recovering from surgery
Chronic inflammation
Under-eating or crash dieting
Overtraining or extreme physical stress
Poor or disrupted sleep
Chronic stress and elevated cortisol (including emotional or physiologic)
Liver and kidney dysfunction
Certain medications
What is "cellular hypothyroidism"?
Cellular hypothyroidism is when your blood levels of TSH, T4 and T3 can look normal, yet your cells aren't receiving enough active thyroid hormone. The result is that you feel hypothyroid, with fatigue, cold intolerance, weight changes, brain fog and hair loss, even though the standard numbers look fine.
That's why in clinic I prefer to look at a fuller picture, which includes:
TSH
Free T4
Free T3
Thyroid antibodies (to check for autoimmune thyroid conditions such as Hashimoto's)
Reverse T3
A Naturopathic approach
High reverse T3 is usually a sign that something else is going on. That's why the real work is asking why it's elevated. In clinic, I look at:
Stress and cortisol patterns: chronic stress can shift thyroid hormone metabolism
Energy availability: are you eating enough, especially enough carbohydrate and protein, to support your thyroid?
Sleep quality: poor sleep is a major stressor on hormonal balance
Nutrient status: iron, selenium, zinc, iodine, vitamin D and B12 all play roles in thyroid function and energy
Gut health and inflammation: these can influence hormone conversion and overall wellbeing
Blood sugar regulation: big swings can add to physiological stress
Book a consultation
If you're doing all the right things and still feeling flat, book a Comprehensive Thyroid Health Assessment or 1:1 Naturopathic Consultation.
Download my free thyroid resources
Thyroid Food Guide - Includes specific nutrients, food sources and why they’re important for your thyroid
Thyroid Health Check - A comprehensive list of common (and uncommon/usually missed) symptoms, plus driving factors increasing your risk of thyroid dysfunction
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