Supplement

Iodine

Iodine is a trace mineral the thyroid gland uses to build its hormones, and too little causes hypothyroidism. Most people look at it for thyroid health, where the evidence is strong that it is essential, though small trials found blood T3 went down in healthy men and T4 went down in people with Hashimoto's disease. Those hormone findings are limited, coming from small studies, including one of just 32 men.

Sources: PMID 3139337

Updated 30 September 2026
How we grade
6 studies cited

Best evidence: Grade C
Conditions studied: 6
Outcomes: 15
Graded outcomes: 0060

Evidence by condition

Strong
Moderate
Limited
Very limited

6 conditions

Metabolic Health

Metabolic Health: outcomes studied for Iodine
Grade	Outcome	Effect	Size	Studies	People
	C-Reactive Protein (CRP) Small Decrease	Improves (the measure goes down)	Small effect	1 study	30 people
Studies that measured c-reactive protein (crp) Iodine intakes of 100-300 μg/d do not modify thyroid function and have modest anti-inflammatory effectsBr J Nutr · PMID 21262066
	Interleukin 6 Small Decrease	Improves (the measure goes down)	Small effect		30 people
	Thyroid-Stimulating Hormone	Improves (the measure goes up)		3 studies	30 people
Studies that measured thyroid-stimulating hormone Breast-milk iodine concentration declines over the first 6 mo postpartum in iodine-deficient womenAm J Clin Nutr · PMID 20702609 The effect of small increases in dietary iodine on thyroid function in euthyroid subjectsMetabolism · PMID 3340004 Iodine supply and thyroid function in women with gestational diabetes mellitus: a cohort study.Endocr Connect · PMID 39212589
	Serum T3	Improves (the measure goes up)		1 study	60 people
Studies that measured serum t3 Effects of low dose oral iodide supplementation on thyroid function in normal menClin Endocrinol · PMID 3139337
	Serum T4	Improves (the measure goes up)			60 people

Immune Health

Immune Health: outcomes studied for Iodine
Grade	Outcome	Effect	Size	Studies	People
	C-Reactive Protein (CRP) Small Decrease	Improves (the measure goes down)	Small effect	1 study	30 people
Studies that measured c-reactive protein (crp) Iodine intakes of 100-300 μg/d do not modify thyroid function and have modest anti-inflammatory effectsBr J Nutr · PMID 21262066
	Interleukin 6	Improves (the measure goes down)			30 people

Thyroid Health

Serum T3: improves
Thyroid-Stimulating Hormone: improves
Serum T4: improves

Thyroid Health: outcomes studied for Iodine
Grade	Outcome	Effect	Size	Studies	People
	Serum T3 Small Decrease	Improves (the measure goes down)	Small effect	1 study	32 people
Studies that measured serum t3 Effects of low dose oral iodide supplementation on thyroid function in normal menClin Endocrinol · PMID 3139337
	Thyroid-Stimulating Hormone	Improves (the measure goes up)		3 studies	32 people
Studies that measured thyroid-stimulating hormone Breast-milk iodine concentration declines over the first 6 mo postpartum in iodine-deficient womenAm J Clin Nutr · PMID 20702609 The effect of small increases in dietary iodine on thyroid function in euthyroid subjectsMetabolism · PMID 3340004 Iodine supply and thyroid function in women with gestational diabetes mellitus: a cohort study.Endocr Connect · PMID 39212589
	Serum T4	Improves (the measure goes up)			32 people

Hashimoto's disease

Serum T4: improves
Thyrotropin Releasing Hormone: improves

Hashimoto's disease: outcomes studied for Iodine
Grade	Outcome	Effect	Size	Studies	People
	Serum T4 Small Decrease	Improves (the measure goes down)	Small effect		300 people
	Thyrotropin Releasing Hormone	Improves (the measure goes up)		1 study	300 people
Studies that measured thyrotropin releasing hormone Effect of low dose iodide supplementation on thyroid function in potentially susceptible subjects: are dietary iodide levels in Britain acceptableClin Endocrinol · PMID 2060151

Lactation (Breast Milk Production)

Serum T4: improves
Thyroid-Stimulating Hormone: improves

Lactation (Breast Milk Production): outcomes studied for Iodine
Grade	Outcome	Effect	Size	Studies	People
	Serum T4 Small Decrease	Improves (the measure goes down)	Small effect		109 people
	Thyroid-Stimulating Hormone	Improves (the measure goes up)		3 studies	109 people
Studies that measured thyroid-stimulating hormone Breast-milk iodine concentration declines over the first 6 mo postpartum in iodine-deficient womenAm J Clin Nutr · PMID 20702609 The effect of small increases in dietary iodine on thyroid function in euthyroid subjectsMetabolism · PMID 3340004 Iodine supply and thyroid function in women with gestational diabetes mellitus: a cohort study.Endocr Connect · PMID 39212589

Gestational Diabetes

Thyroid-Stimulating Hormone: improves

Gestational Diabetes: outcomes studied for Iodine
Grade	Outcome	Effect	Size	Studies	People	Studies list
	Thyroid-Stimulating Hormone	Improves (the measure goes up)		3 studies	437 people
Studies that measured thyroid-stimulating hormone Breast-milk iodine concentration declines over the first 6 mo postpartum in iodine-deficient womenAm J Clin Nutr · PMID 20702609 The effect of small increases in dietary iodine on thyroid function in euthyroid subjectsMetabolism · PMID 3340004 Iodine supply and thyroid function in women with gestational diabetes mellitus: a cohort study.Endocr Connect · PMID 39212589

Key findings

C-Reactive Protein (CRP)Metabolic HealthImproves (the measure goes down)
Serum T3Thyroid HealthImproves (the measure goes down)
Interleukin 6Metabolic HealthImproves (the measure goes down)

Shop Iodine

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Grade C

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Studies cited

6 studies from PubMed

Breast-milk iodine concentration declines over the first 6 mo postpartum in iodine-deficient womenAm J Clin Nutr · PMID 20702609
Effect of low dose iodide supplementation on thyroid function in potentially susceptible subjects: are dietary iodide levels in Britain acceptableClin Endocrinol · PMID 2060151
The effect of small increases in dietary iodine on thyroid function in euthyroid subjectsMetabolism · PMID 3340004
Effects of low dose oral iodide supplementation on thyroid function in normal menClin Endocrinol · PMID 3139337
Iodine intakes of 100-300 μg/d do not modify thyroid function and have modest anti-inflammatory effectsBr J Nutr · PMID 21262066
Iodine supply and thyroid function in women with gestational diabetes mellitus: a cohort study.Endocr Connect · PMID 39212589