The Healthspan Map · Nutrient

Iodine

Linked to getting too little

Where a shortfall of Iodine is linked — 6 sources.In the order the Map holds them: strongest evidence first. That is a statement about the evidence, not about what matters most.
Nutrient or lever	Direction	Strength	Evidence type	What was found	Source
Iodine	Eat enough of	Moderate	Established clinical	Deficiency lowers IQ and causes cognitive impairment in children and cognitive slowing in adults.	NIH ODS / Harvard – Iodine (opens in a new tab)
Iodine	Eat enough of	Moderate	Established clinical	Deficiency lowers IQ and causes cognitive impairment in children and cognitive slowing in adults.	NIH Office of Dietary Supplements — Iodine (opens in a new tab)
Iodine	Eat enough of	Emerging	Review / narrative	Iodine deficiency lowers thyroid hormone output, a classic cause of tiredness and low energy (cross-links to Thyroid).	Nutrition & thyroid review (PMC11314468) (opens in a new tab)
Iodine	Eat enough of	Moderate	Established clinical	Hypothyroidism from deficiency causes depression and low mood.	NIH ODS – Iodine (opens in a new tab)
Iodine	Eat enough of	Strong	Established clinical	Iodine is the substrate for T3/T4; deficiency causes goiter, nodular disease and hypothyroidism.	Thyroid nutrition review (J Endocrinol Invest 2026) (opens in a new tab)
Iodine	Eat enough of	Strong	Established clinical	Severe deficiency in pregnancy causes cretinism (irreversible physical/neurological impairment), miscarriage, stillbirth and neonatal hypothyroidism — the world's leading preventable cause of brain damage.	Severe-iodine-deficiency-in-pregnancy review (opens in a new tab)

Where an excess of Iodine is linked — 2 sources.In the order the Map holds them: strongest evidence first. That is a statement about the evidence, not about what matters most.
Nutrient or lever	Direction	Strength	Evidence type	What was found	Source
Iodine	Don't overdo	Emerging	Established clinical	Excess iodine irritates the GI tract, causing nausea, vomiting, diarrhoea and abdominal upset.	Iodine toxicity & GI (opens in a new tab)
Iodine	Don't overdo	Strong	Established clinical	Excess iodine (kelp/supplements) can precipitate hyperthyroidism or trigger autoimmune thyroiditis/hypothyroidism via thyrocyte ROS — the high end of the U-curve.	Thyroid nutrition review (J Endocrinol Invest 2026) (opens in a new tab)