Iodine and the thyroid — a gap hiding in plain sight
Iodine deficiency was solved in the West by iodised salt. Then processed food replaced home cooking and took the iodised salt with it.
nutrition
Iodised salt is used in home cooking. Processed food — which now constitutes the majority of caloric intake in most Western countries — uses non-iodised salt. The net dietary iodine supply has quietly declined as the food environment shifted, without any change in official guidance.
Bromine (used in commercial bread flour) and fluoride (in water supplies) are halogens that compete with iodine for thyroid receptor sites — effectively displacing it even when intake appears adequate. The thyroid produces hormones that regulate the metabolic rate of every cell in the body. Suboptimal iodine is a systemic drag, not a local problem.
Subclinical hypothyroidism — thyroid function technically within reference range but meaningfully below optimal — is associated with fatigue, brain fog, weight gain, depression, and cold intolerance. TSH reference ranges are wide and contested within endocrinology. Many people experiencing these symptoms are told their thyroid is normal.
Best dietary sources: seaweed (nori, wakame, kelp), white fish, dairy, eggs
Bromine in commercial flour competes directly with iodine for receptor sites
Fluoride in water supply adds further competitive displacement
Iodine is best taken in the morning — thyroid hormone synthesis ramps up under the morning cortisol curve