Hormone Health Hub: Expert Insights on Testing, Balance & Better Living — thyroid and fatigue

Reverse T3 (rT3) is one of the most misunderstood markers in thyroid testing. Often called the “hibernation hormone,” it is frequently claimed — without scientific basis — to block thyroid receptors and slow metabolism. In Part 2 of this series, Margaret Groves of ZRT Laboratory examines what the peer-reviewed literature actually says about rT3, when elevated levels are clinically meaningful, and how to interpret the T3/rT3 ratio in the context of a comprehensive thyroid assessment.

Thyroid symptoms can persist even when thyroxine (T4) levels appear normal — because thyroid function is profoundly affected by anything that disrupts the conversion of T4 to the active hormone T3 at the cellular level. In Part 1 of this two-part series, Margaret Groves of ZRT Laboratory explains the three deiodinase enzymes (D1, D2 and D3) that act as gatekeepers to intracellular thyroid hormone bioavailability, what affects circulating levels of T3 and reverse T3, and why selenium, iodine and inflammatory conditions all play a critical role.

Normal thyroid blood tests don’t always explain why patients still suffer from fatigue, cold intolerance, brain fog and weight gain. In this in-depth clinical article, ZRT Laboratory explains the critical role of selenium in thyroid hormone synthesis and T4-to-T3 conversion, how heavy metals like mercury and arsenic sequester selenium and inactivate protective antioxidant enzymes, and why this can trigger Hashimoto’s thyroiditis — even when TSH, T4 and T3 appear normal.

Thyroid cancer is now among the top 10 most common cancers worldwide, with incidence rising by an average of 5.5% per year. But experts are divided: is this a genuine epidemic, or an epidemic of diagnosis driven by more sensitive imaging? This article reviews the evidence on both sides, explores the role of iodine deficiency, radiation exposure and environmental factors, and explains why thyroid awareness — and monitoring — matters year-round.

Millions of people struggle with weight gain, fatigue and low mood despite being told their thyroid test results are “normal.” The problem is that a standard TSH test alone cannot identify the full range of factors that suppress thyroid function — from oestrogen dominance and elevated cortisol to iodine deficiency, selenium deficiency, heavy metal toxicity and xenoestrogen burden. This article explains what those hidden saboteurs are and how targeted testing can help identify them.