Discover the best selenium and zinc supplements for thyroid support in 2026. Learn which nutrients optimize T3 conversion, reduce TPO antibodies, and address the hidden ferritin-TPO connection your doctor might miss. Evidence-based guide covers ashwagandha for stress-thyroid axis, iodine safety, thyroid thieves blocking receptors, and symptom-based supplement selection. Includes third-party tested recommendations from Pure Encapsulations, Thorne Research, and expert dosing pr