The thyroid is a small butterfly-shaped gland located in the front of the neck, just below the Adam's apple. It plays a crucial role in regulating various bodily functions by producing hormones that control metabolism and energy production. Thyroid hormones, primarily thyroxine (T4) and triiodothyronine (T3), influence the functioning of almost every organ in the body, including the heart, brain, muscles, and skin.The thyroid gland functions under the control of the hypothalamus and the pituitary gland. The hypothalamus releases thyrotropin-releasing hormone (TRH), which signals the pituitary gland to release thyroid-stimulating hormone (TSH). TSH then stimulates the thyroid gland to produce...
Most people associate iodine exclusively with thyroid health — but this essential mineral plays a far broader role in the body. From breast tissue and ovarian function to fetal brain development and endometrial health, iodine is active in virtually every organ system. Deficiency is more widespread than commonly recognised, and standard thyroid blood tests cannot reliably detect it. This guide explores the extrathyroidal roles of iodine, the difference between iodide and molecular iodine, the controversy around dosing, and why testing urinary iodine is the most accurate way to assess your status.
Saliva hormone testing is one of the most accurate and convenient ways to measure bioavailable hormones — the fraction that is actually active in your body's tissues. Unlike standard blood tests, which measure total hormone levels including protein-bound fractions that cells cannot use, saliva testing captures only the free, unbound hormones that drive real physiological effects. This guide explains how saliva testing works, which hormones it measures, why it is clinically superior for monitoring hormone therapy, and how to choose the right test for your health goals.
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.
