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Iodine (Kelp)

Supporting healthy thyroid function through its role in thyroid hormone production.

Evidence · Grade D
Human trial evidenceTraditional useInteraction riskNeeds more research

Sea-vegetable source of iodine essential for thyroid hormone synthesis, traditional in hypothyroidism support.

Iodine is an essential trace element that the body cannot produce on its own. It is commonly associated with thyroid health, as it is a crucial component of thyroid hormones. When obtained from natural sources like kelp, it is often consumed as a dietary supplement in capsule, tablet, or liquid forms, primarily to support thyroid function and prevent deficiency.

Quick answer

What it is: Iodine is an essential trace element that the body cannot produce on its own.

May support:Primary Hypothyroidism, Thyroid Nodules, Autoimmune Thyroid Disease, Hypothyroidism, Subclinical Hypothyroidism

Evidence:Evidence · Grade D

Evidence Summary

Evidence · Grade D

Much of the understanding of iodine's role comes from observational studies on populations with iodine deficiency and its impact on thyroid health. While its essentiality is well-established, studies on supplementation for non-deficiency states, particularly in relation to specific health outcomes beyond preventing deficiency, are often limited, contributing to the 'D' grade.

Last reviewed · Jun 2026

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Why It Works

Iodine is a fundamental building block for the thyroid hormones T3 and T4, which are involved in regulating metabolism and energy production throughout the body.

How it works in more detail

At the thyroid follicle, iodide, absorbed from the diet, is actively transported into thyroid cells. It is then oxidized and incorporated into tyrosine residues on thyroglobulin, leading to the formation of monoiodotyrosine (MIT) and diiodotyrosine (DIT). The coupling of MIT and DIT forms the active thyroid hormones thyroxine (T4) and triiodothyronine (T3). This process is vital for the synthesis and secretion of thyroid hormones, which regulate numerous physiological processes.

How to use

Always consult a qualified clinician.

Editorial guidance

Suggested dosage
150–300 mcg/day from kelp; do not exceed 1100 mcg/day total iodine. Consult a doctor before use with thyroid conditions.
Research dosage range
150-1100 mcg/day elemental iodine
Typical onset
For correcting frank iodine deficiency, improvements in thyroid function markers may be observed over several weeks to months of consistent supplementation. For other potential benefits, onset timing is not well-established.
Typical forms
Capsule, Tablet, Powder (kelp), Liquid extract (kelp)
Quality markers
For kelp-derived iodine, look for products that specify the iodine content per serving and are tested for heavy metals and contaminants. Third-party testing for purity and potency is a strong indicator of quality. Organic certification may also be desirable for kelp products.
Medication interactions
  • Antithyroid medications (e.g., methimazole, propylthiouracil)
  • Lithium
  • Amiodarone
  • ACE inhibitors
  • Potassium-sparing diuretics
Avoid if
  • Hyperthyroidism
  • Autoimmune thyroid disease (e.g., Hashimoto's thyroiditis, Graves' disease) without medical supervision
  • Dermatitis herpetiformis
  • Iodine allergy

Community tips

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Suggested dosage

150–300 mcg/day from kelp; do not exceed 1100 mcg/day total iodine. Consult a doctor before use with thyroid conditions.

General guidance — discuss specifics with a clinician.

Active medicinal compounds

Iodine, trace minerals from Laminaria/kelp species.

Traditional use

Coastal cultures (Japan, Iceland, Ireland) have used seaweeds nutritionally for millennia.

Safety

Safety warnings

Excess iodine can paradoxically worsen Hashimoto's or trigger hyperthyroidism. Test before supplementing.

Avoid if

  • Hyperthyroidism
  • Autoimmune thyroid disease (e.g., Hashimoto's thyroiditis, Graves' disease) without medical supervision
  • Dermatitis herpetiformis
  • Iodine allergy

Medication interactions

  • Antithyroid medications (e.g., methimazole, propylthiouracil)
  • Lithium
  • Amiodarone
  • ACE inhibitors
  • Potassium-sparing diuretics

Reported side effects

  • Nausea
  • Diarrhea
  • Stomach pain
  • Goiter (with excessive intake)
  • Hyperthyroidism (with excessive intake)
  • Hypothyroidism (with excessive intake, especially in susceptible individuals)
  • Allergic reactions (rare)

General guidance — discuss specifics with a clinician.

Evidence ecosystem

Scientific literature, clinical guidance, government sources, ongoing research, traditional use, and lived experience — grouped by source type and quality.

Overall grade (D)

Much of the understanding of iodine's role comes from observational studies on populations with iodine deficiency and its impact on thyroid health. While its essentiality is well-established, studies on supplementation for non-deficiency states, particularly in relation to specific health outcomes beyond preventing deficiency, are often limited, contributing to the 'D' grade.

Filter by source type

Clinical Guidelines(4)

Recommendations from medical societies (NICE, AHA, ADA, ACG, Endocrine Society…).

High Quality
  • American Thyroid Association 2026 Guidelines for Thyroid Disease in Preconception, Pregnancy, and Postpartum.

    Korevaar TIM, Leung AM, Alexander EK, Bliddal S, Boelaert K, Brenta G · Thyroid : official journal of the American Thyroid Association · 2026

    Thyroid disease in pregnancy, preconception, and postpartum is a common and clinically relevant problem. Since the publication of the American Thyroid Association (ATA) guidelines in 2017, substantial new clinical and scientific evidence has become available. The aim of these guidelines is to provide clinicians, patients, researchers, and policymakers with evidence-based recommendations on the care of women with thyroid disease before, during, and after pregnancy. The clinical questions addressed were informed by prior ATA guidelines, stakeholder feedback, a global needs assessment, and input from the multidisciplinary task force. Systematic literature searches were conducted with the support from a medical librarian and evaluated using the Grading of Recommendations, Assessment, Development, and Evaluation framework. Recommendations were formulated based on the quality of evidence, balance of benefits and harms, patient values, feasibility, and equity. Where data were limited, Good P

    Clinical GuidelinePubMed (Practice Guideline)Very High Quality
  • [Detection of thyroid dysfunction in pregnant women: universal screening is justified].

    Vila L, Velasco I, González S, Morales F, Sánchez E, Lailla JM · Medicina clinica · 2012

    There is a controversy among different scientific societies in relation to the recommendations on whether universal screening for the detection of thyroid dysfunction during gestation should be performed or not. Although various studies have shown an association between subclinical hypothyroidism or hypothyroxinemia with obstetric problems and/or neurocognitive impairment in the offspring, no evidence on the possible positive effects of treatment of such conditions with thyroxin has been demonstrated so far. However, there is a general agreement about the need for treatment of clinical hypothyroidism during pregnancy and the risks of not doing so. Because it is a common, easily diagnosed and effectively treated disorder without special risk, the working Group of Iodine Deficiency Disorders and Thyroid Dysfunction of the Spanish Society of Endocrinology and Nutrition and Spanish Society of Gynaecology and Obstetrics recommends an early evaluation (before week 10) of thyroid function in

    Clinical GuidelinePubMed (Practice Guideline)Very High Quality
  • Detection of thyroid dysfunction in pregnant women: universal screening is justified.

    Vila L, Velasco I, González S, Morales F, Sánchez E, Lailla JM · Endocrinologia y nutricion : organo de la Sociedad Espanola de Endocrinologia y Nutricion · 2012

    There is a controversy among different scientific societies in relation to the recommendations on whether universal screening for the detection of thyroid dysfunction during gestation should be performed or not. Although various studies have shown an association between subclinical hypothyroidism or hypothyroxinemia with obstetric problems and/or neurocognitive impairment in the offspring, no evidence on the possible positive effects of treatment of such conditions with thyroxin has been demonstrated so far. However, there is a general agreement about the need for treatment of clinical hypothyroidism during pregnancy and the risks of not doing so. Because it is a common, easily diagnosed and effectively treated disorder without special risk, the working Group of Iodine Deficiency Disorders and Thyroid Dysfunction of the Spanish Society of Endocrinology and Nutrition and Spanish Society of Gynaecology and Obstetrics recommends an early evaluation (before week 10) of thyroid function in

    Clinical GuidelinePubMed (Practice Guideline)Very High Quality

Observational Studies(12)

Cohort, case-control, and cross-sectional human studies.

Moderate Quality
  • Optimizing Growth: The Case for Iodine.

    Rigutto-Farebrother J · Nutrients · 2023

    Iodine is an essential micronutrient and component of thyroid hormone. An adequate dietary iodine intake is critical to maintain and promote normal growth and development, especially during vulnerable life stages such as pregnancy and early infancy. The role of iodine in cognitive development is supported by numerous interventional and observational studies, and when iodine intake is too low, somatic growth is also impaired. This can be clearly seen in cases of untreated congenital hypothyroidism related to severe iodine deficiency, which is characterized, in part, by a short stature. Nevertheless, the impact of a less severe iodine deficiency on growth, whether in utero or postnatal, is unclear. Robust studies examining the relationship between iodine and growth are rarely feasible, including the aspect of examining the effect of a single micronutrient on a process that is reliant on multiple nutrients for optimal success. Conversely, excessive iodine intake can affect thyroid functio

    Observational StudyPubMedLow Quality
  • Hypothyroidism.

    Chaker L, Razvi S, Bensenor IM, Azizi F, Pearce EN, Peeters RP · Nature reviews. Disease primers · 2022

    Hypothyroidism is the common clinical condition of thyroid hormone deficiency and, if left untreated, can lead to serious adverse health effects on multiple organ systems, with the cardiovascular system as the most robustly studied target. Overt primary hypothyroidism is defined as elevated thyroid-stimulating hormone (TSH) concentration in combination with free thyroxine (fT4) concentration below the reference range. Subclinical hypothyroidism, commonly considered an early sign of thyroid failure, is defined by elevated TSH concentrations but fT4 concentrations within the reference range. Hypothyroidism is classified as primary, central or peripheral based on pathology in the thyroid, the pituitary or hypothalamus, or peripheral tissue, respectively. Acquired primary hypothyroidism is the most prevalent form and can be caused by severe iodine deficiency but is more frequently caused by chronic autoimmune thyroiditis in iodine-replete areas. The onset of hypothyroidism is insidious in

    Observational StudyPubMedLow Quality
  • Thyroid, Diet, and Alternative Approaches.

    Larsen D, Singh S, Brito M · The Journal of clinical endocrinology and metabolism · 2022

    Increasingly, patients are asking their physicians about the benefits of dietary and alternative approaches to manage their diseases, including thyroid disease. We seek to review the evidence behind several of the vitamins, minerals, complementary medicines, and elimination diets that patients are most commonly using for the treatment of thyroid disorders. Several trace elements are essential to normal thyroid function, and their supplementation has been studied in various capacities. Iodine supplementation has been implemented on national scales through universal salt iodization with great success in preventing severe thyroid disease, but can conversely cause thyroid disorders when given in excess. Selenium and zinc supplementation has been found to be beneficial in specific populations with otherwise limited generalizability. Other minerals, such as vitamin B12, low-dose naltrexone, and ashwagandha root extract, have little to no evidence of any impact on thyroid disorders. Avoidanc

    Observational StudyPubMedLow Quality

Government Health Sources(1)

Public-health agencies: NCCIH, NIH, CDC, NHS.

High Quality
  • Iodine deficiency

    World Health Organization (WHO)

    While not directly about primary hypothyroidism, this WHO page provides data and information on iodine deficiency, a major cause of preventable hypothyroidism worldwide, and global efforts to address it.

    Government SourceWorld Health Organization (WHO)High Quality

Clinical Trial Registries(21)

Registered ongoing or completed trials (ClinicalTrials.gov).

Moderate Quality
  • Comparison of I-124 and I-131 Radiopharmacokinetics In Patient With Well Differentiated Thyroid Cancer After Thyroid Hormone Withdrawal

    n=16 · NCT02947399 · TERMINATED · TERMINATED

    This research study is to compare the radiopharmacokinetics of I-124 to the radiopharmacokinetics of I-131 in patients who have well-differentiated thyroid cancer after thyroid hormone withdrawal. I-131 is routinely used for imaging and dosimetry for patients with well-differentiated thyroid cancer. In this study, I-124 is administered orally in capsular form, and the radiopharmacokinetics of I-124 is compared with I-131. I-124 is another isotope of iodine, which is cyclotron-produced. I-124 has multiple advantages: * Ideal Half-Life (4.2 days) for delayed imaging. * High resolution tomographic imaging. * Feasibility of quantitating lesion uptake. * Potential of dosimetry for the planning of radioiodine therapy. Voluntary patients will have I-124 dosimetry performed in addition to the I-131 dosimetry, which is planned as part of routine clinical care. I-124 dosimetry is composed of three parts: (1) the administration of I-124, (2) imaging, and (3) drawing blood samples. Patients will start 3-5 weeks of thyroid hormone withdrawal. This is similar to the procedure for I-131 dosimetry. Second, they will receive I-124. I-124 is similar to I-131 except I-124 decays in a different way to emit a positron so that the PET scanner can be used for imaging. I-124 is given in the form of one or several capsules, which are taken by mouth. This is also similar to I-131. Third, PET/CT imaging is done for approximately 30 minutes to one hour on five consecutive days. Radiation from PET/CT scan is far less than what they receive from a diagnostic CT scan. For the fourth part, a technologist will draw about 5 cc from the forearm on each of the five consecutive days. This is also similar to I-131. Initially, all patients will be randomized to one of two study groups. The first group will have the I-131 dosimetry performed first followed by the I-124 dosimetry, and the second group will have the I-124 dosimetry performed first followed by the I-131 dosimetry. The risk of this study is considered very low, and the potential benefits to the patient are considered very high.

    Clinical TrialClinicalTrials.govModerate Quality
  • Effect of Household Use of Multiple Micronutrient-fortified Bouillon on Micronutrient Status Among Women and Children in Two Districts in the Northern Region of Ghana

    n=2372 · NCT05178407 · COMPLETED · COMPLETED

    Background: Micronutrient (MN) deficiencies are severe and widespread in West Africa, particularly among young children and women of reproductive age. Bouillon is a promising food fortification vehicle because the product is centrally processed on large scale, consumed by most households in West African countries (even rural, poor households), and consumed by most members of the household in relatively constant amounts. However, several important research questions remain regarding whether the use of fortified bouillon would be feasible and effective for preventing or reducing micronutrient deficiencies in communities where such deficiencies are common. Specifically, no studies have assessed the impacts of multiple micronutrient-fortified bouillon on micronutrient status. The West Africa Condiment Micronutrient Innovation Trial (CoMIT) Project aims to address this gap, to inform future discussions around fortification of bouillon cubes and related products. Objective: This study aims to assess the impacts of household use of multiple micronutrient-fortified bouillon cubes (containing iodine in addition to vitamin A, folic acid, vitamin B12, iron, and zinc), compared to control bouillon cubes fortified with iodine only, on: 1. Micronutrient status among women 15-49 years of age and children 2-5 years of age after 9 months of intervention 2. Hemoglobin concentrations among women 15-49 years of age and children 2-5 years of age after 9 months of intervention 3. Breast milk micronutrient concentrations among lactating women 4-18 months postpartum after 3 months of intervention Methods: This randomized, controlled doubly-masked trial will be conducted in the Kumbungu and Tolon districts in the Northern Region of Ghana, where prior data indicate that deficiencies in the selected nutrients are common. Potential participants will be: 1) non-pregnant non-lactating women of reproductive age (15 - 49 years old), 2) children 2-5 years of age, and 3) non-pregnant lactating women 4-18 months postpartum. Eligible participants will be randomly assigned to receive household rations of one of two types of bouillon cubes: 1. a multiple micronutrient-fortified bouillon cube containing vitamin A, folic acid, vitamin B12, iron, zinc, and iodine, or 2. a control cube containing iodine only Each participant's household will receive a specific amount of bouillon cube every 2 weeks, and households will be advised to prepare their meals as usual, using the study-provided cubes. The trial duration will be 9 months (38 weeks) for non-pregnant, non-lactating women and children 2-5 years of age, and 3 months (12 weeks) for lactating women. The primary outcomes will be changes from baseline to endline in concentrations of haemoglobin and biomarkers of micronutrient status. Secondary outcomes will include change in prevalence of anaemia and micronutrient deficiency; dietary intake of bouillon and micronutrients; inflammation, malaria, and morbidity symptoms; and children's anthropometric measures and child development.

    Clinical TrialClinicalTrials.govModerate Quality
  • Value of the Combination Ultrasonography With Ti-RADS Score / Dual Tracer Scintigraphy MIBI-Tc99m/Iodine-123 in the Detection of Malignancy of Thyroid Nodules (Sup or Egal to 15 mm) Classified Bethesda III or IV on Cytology

    n=372 · NCT03498183 · COMPLETED · COMPLETED

    The main objective of the study is to show that the addition of ultrasonography to the dual tracer scintigraphy MIBI-Tc99m/Iodine-123 will increase (at least +5%) the negative predictive value compared to the dual tracer scintigraphy alone in detection of malignancy in thyroid nodules ≥15 mm classified as Bethesda III-IV on cytology.

    Clinical TrialClinicalTrials.govModerate Quality

Limitations: Current evidence for iodine supplementation, especially from kelp, beyond addressing deficiency, often includes small study sizes, heterogeneity in study design, and a lack of robust, long-term randomized controlled trials in non-deficient populations. There is also variability in iodine content in kelp products, which can complicate research and dosage.

This page is educational. Statements use phrases like "may support" and "has been studied for"because no remedy here is approved to cure, treat, or reverse any condition. Discussion happens on the ailment pages — community statistics here are derived from those reports. Always consult a qualified clinician.

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