Thyroid & Heavy Metals Thyroid issues don’t always start in the thyroid. Growing research shows that heavy metals can interfere directly with thyroid signaling, hormone production, and immune regulation . A study published in the Journal of Trace Elements in Medicine and Biology  found that elevated levels of mercury, lead, and cadmium  were associated with a higher risk of thyroid dysfunction. What the research shows: • Mercury  has been linked to autoimmune thyroid conditio