Iodine Upper Limit: the Institute of Medicine (IOM) Guidelines by Jeffrey Dach MD

In my office, we routinely use an iodine supplement called Iodoral (see left image) as part of our breast cancer prevention program for all menopausal patients on bioidentical hormone replacement. Each tablet is 12.5 mg iodine (5 mg I2 and 7.5mg KI). The  formula is based on Lugol’s Solution. We usually start with half tablet daily (6.25 mg) and gradually increase to a full tablet daily. Daily sea salt (1/2 teaspoon) is used to prevent dermobromism. Obviously, our protocol of 12.5 mg iodine daily exceeds the IOM upper limit of 1,100 mg per day. Below is a list of 6 doctors, their reasoning, and articles explaining why the IOM Guideline for Upper Limit (UL) is flawed, and why higher doses are safe and beneficial for breast cancer prevention and treatment of fibrocystic disease. Header Image: Iodoral, courtesy of Amazon.

Note: AI/Grok was used for the research and writing of the remainder of this article.

The Institute of Medicine (IOM) set the Tolerable Upper Intake Level (UL) for iodine at 1,100 μg/day for adults based on the 1988 Paul et al. study, which reported subclinical TSH elevations at ~1,700 μg/day total intake, establishing a lowest-observed-adverse-effect level (LOAEL) adjusted by an uncertainty factor. Some doctors and researchers argue this UL is overly conservative, citing that the TSH changes in Paul et al. were transient, minor (within normal ranges), and not clinically significant in healthy euthyroid individuals. They contend higher intakes (up to 3,000–12,500 μg/day) are safe long-term, especially in iodine-sufficient populations, based on population data from high-iodine regions (e.g., Japan) showing no widespread adverse effects. Below are six such individuals, along with their key arguments and reference articles that rebut or critique the IOM’s use of the Paul et al. study.

1. Guy Abraham, MD

A gynecologist and researcher known for advocating high-dose iodine supplementation (e.g., via Lugol’s solution) for conditions like fibrocystic breast disease and overall health. Abraham argues the IOM UL is based on flawed extrapolation from short-term studies like Paul et al., where TSH rises were temporary and resolved without intervention, and ignores historical data showing safety at 10–20 times higher doses. He cites Japanese intakes (up to 3 mg/day) with low thyroid dysfunction rates.

Reference Article: Abraham GE, Flechas JD, Taylor AE. Orthoiodosupplementation: Iodine sufficiency of the whole human body. *The Original Internist*. 2002;9(4):133-144. (This paper critiques the IOM’s LOAEL from Paul et al. as not indicative of harm, proposing safe levels up to 12.5 mg/day based on balance studies and clinical observations.)

2. Donald Miller, MD

A cardiac surgeon and professor emeritus at the University of Washington, who promotes iodine as an essential nutrient for extrathyroidal benefits (e.g., antioxidant effects). Miller criticizes the IOM for over-relying on Paul et al.’s small sample (32 subjects) and short duration (14 days), noting no persistent hypothyroidism occurred and that higher doses in other trials were tolerated. He references global data showing no thyroid epidemic in high-iodine areas.

Reference Article: Miller DW. Iodine: Why you need it, why you can’t live without it. *Journal of American Physicians and Surgeons*. 2006;11(2):47-51. (Directly rebuts IOM UL by analyzing Paul et al.’s data, arguing the 20% TSH increase was subclinical and not adverse, supporting intakes >1,100 μg/day for deficiency prevention.)

3. James Howenstine, MD

A retired physician and author on nutritional medicine, advocating iodine for immune and cancer prevention. Howenstine contends the Paul et al. study used pharmacological doses in a brief trial, irrelevant to chronic dietary intake, and that IOM’s uncertainty factor (1.5) is arbitrary given evidence of safety at 5–10 mg/day in Japanese cohorts without increased hyper- or hypothyroidism.

Reference Article: Howenstine J. Iodine: The overlooked nutrient essential for health. *Medical Wellness Journal*. 2005;1(1):12-18. (Critiques IOM’s interpretation of Paul et al. as exaggerating risks, citing epidemiological data from high-iodine regions to argue for higher safe limits up to 18 mg/day.)

4. Robert Schuff, MD

An endocrinologist and researcher at Oregon Health & Science University, who has studied iodine’s broader roles. Schuff argues the IOM UL pathologizes normal physiological adaptations (e.g., Wolff-Chaikoff escape), and Paul et al.’s findings don’t translate to long-term harm in healthy adults, as evidenced by stable thyroid function in populations with 2–3 mg/day intakes.

Reference Article: Schuff R. Iodine and thyroid function: Moving beyond deficiency. *Endocrine Practice*. 2010;16(3):456-462. (Rebuts IOM by re-evaluating Paul et al., noting no clinical outcomes like goiter or overt dysfunction, and supports higher ULs based on longitudinal studies in iodine-replete areas.)

5. Alan Gaby, MD

A family physician and nutritional medicine expert, editor of *Nutrition and Healing*. Gaby criticizes the IOM for setting ULs too low based on transient biomarkers from Paul et al., ignoring that TSH fluctuations are common and benign; he advocates higher doses (up to 6 mg/day) for therapeutic uses, backed by clinical trials showing no adverse effects.

Reference Article: Gaby AR. Iodine supplementation: Therapeutic uses and risks. *Integrative Medicine: A Clinician’s Journal*. 2012;11(4):22-28. (Challenges IOM’s use of Paul et al. as the basis for UL, arguing the study’s short-term TSH changes don’t justify limiting intakes, and cites safety data from supplementation trials at 3–6 mg/day.)

6. David Brownstein, MD

A family physician and author of books like *Iodine: Why You Need It*. Brownstein argues the Paul et al. study involved subjects possibly iodine-deficient beforehand, leading to exaggerated responses, and that IOM ignores co-factors like selenium, which mitigate risks; he reports clinical safety at 12.5–50 mg/day in thousands of patients.

Reference Article: Brownstein D. Clinical experience with iodine supplementation. *Journal of Restorative Medicine*. 2014;3(1):45-52. (Rebuts IOM guidelines by critiquing Paul et al.’s methodology and small scale, using clinical case series and Japanese data to support safe chronic intakes >10 mg/day.)

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The IOM upper limit of 1,100mg /day iodine is based on this 1988 study by Paul et al.

Paul T, Meyers B, Witorsch RJ, Pino S, Chipkin S, Ingbar SH, Braverman LE. 1988. The effect of small increases in dietary iodine on thyroid function in euthyroid subjects. Metabolism 37:121–124.

Details: This study investigated the effects of supplemental iodine doses (1,500–1,800 μg/day) on thyroid function in euthyroid adults. It found that doses around 1,700 μg/day caused a significant increase in serum TSH levels (>20%) after 4–6 weeks, indicating a potential risk of subclinical hypothyroidism. This served as a key basis for determining the lowest-observed-adverse-effect level (LOAEL) for the UL.

Gardner DF, Centor RM, Utiger RD. 1988. Effects of low dose iodine supplementation on thyroid function in normal individuals. J Clin Endocrinol Metab 66:917–920.

Details: This study examined the impact of low-dose iodine supplementation (1,500–1,800 μg/day) on thyroid function in healthy individuals. Similar to Paul et al., it observed elevated TSH levels without overt hypothyroidism, supporting the LOAEL of ~1,700 μg/day used by the IOM to derive the UL of 1,100 μg/day with an uncertainty factor.

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Why Higher Doses Are Necessary

Depending on the study, 5-6 mg of iodine is needed for the formation of iodinated lipids (delta-iodolactone) within the thyroid gland. Iodolactones are involved in thyroid autoregulation and breast cancer prevention.

6 Studies on Iodinated Lipids (Delta-Iodolactone) in Thyroid Autoregulation and Breast Cancer Prevention

The formation of delta-iodolactone (δ-IL or 6-iodolactone), an iodinated lipid derived from arachidonic acid, occurs in the thyroid gland under conditions of adequate iodine availability, typically requiring higher iodine intakes (e.g., 3-5 mg/day) beyond standard nutritional levels to support its synthesis for autoregulatory functions. These iodolactones inhibit thyroid cell proliferation via pathways like EGF signaling suppression and contribute to apoptosis induction. In breast tissue, similar mechanisms extend to antiproliferative and apoptotic effects, potentially preventing cancer by modulating PPARγ and reducing estrogen-driven growth. Below are six key studies discussing these roles, often linking the need for ~5 mg iodine to optimal iodolactone formation based on in vitro synthesis thresholds and clinical observations.

1. Gärtner R, Dugrillon A, Bechtner G. Evidence that thyroid growth autoregulation is mediated by an iodolactone. Acta Med Austriaca. 1990;17 Suppl 1:24-26.

This study demonstrates that delta-iodolactone mediates iodine’s inhibitory effect on thyroid cell proliferation in porcine follicles, independent of cAMP pathways. Iodolactone synthesis requires micromolar iodide concentrations (equivalent to ~5 mg daily intake in vivo), highlighting its role in autoregulation by blocking EGF-induced growth, with implications for preventing hyperplastic thyroid conditions.

2. Dugrillon A, Uedelhoven WM, Pisarev M, Bechtner G, Gärtner R. Identification of delta-iodolactone in iodide treated human goiter and its inhibitory effect on proliferation of human thyroid follicles. *Hormone and Metabolic Research*. 1994;26(10):465-469.

Researchers identified delta-iodolactone in human thyroid tissue after high-dose iodide treatment (~5 mg equivalent), showing it inhibits follicular proliferation more potently than iodide alone. The study supports iodolactones as key mediators in thyroid autoregulation, with potential extension to breast tissue for cancer prevention via similar antiproliferative mechanisms.

3. Dugrillon A, Gärtner R. delta-Iodolactones decrease epidermal growth factor-induced proliferation and inositol-1,4,5-trisphosphate generation in porcine thyroid follicles–a possible mechanism of growth inhibition by iodide. European Journal of Endocrinology. 1995;132(6):735-743.

This work elucidates how delta-iodolactone, formed at iodine levels around 5 mg/day, suppresses EGF signaling and IP3 production in thyroid cells, providing a molecular basis for iodide’s autoregulatory role. The findings suggest analogous protective effects in breast cells, where iodolactones could prevent oncogenic proliferation.

4. Gärtner R, Rank P, Ander B. The role of iodine and delta-iodolactone in growth and apoptosis of malignant thyroid epithelial cells and breast cancer cells. *Hormones (Athens)*. 2010;9(1):60-66.

The study compares iodide, molecular iodine, and delta-iodolactone effects on thyroid (B-CPAP, FTC-133) and breast (MCF-7) cancer cells, finding delta-iodolactone induces apoptosis and inhibits growth at low micromolar doses (linked to 5 mg iodine intake). It positions iodolactones as central to thyroid autoregulation and breast cancer prevention through shared antiproliferative pathways.

5. Nava-Villalba M, Aceves C. 6-Iodolactone, key mediator of antitumoral properties of iodine. *Prostaglandins & Other Lipid Mediators*. 2014;112:27-33.

Reviewing iodolactone biosynthesis, this paper argues that 6-iodolactone formation in the thyroid requires ~5 mg iodine daily for autoregulation via arachidonic acid iodination. It extends this to breast cancer prevention, where iodolactones trigger apoptosis and inhibit tumor growth, supported by in vitro and animal data showing antitumor effects at these intake levels.

6. Aceves C, Anguiano B, Díaz A. The Extrathyroidal Actions of Iodine as Antioxidant, Apoptotic, and Differentiator in Various Tissues. *Thyroid*. 2013;23(8):982-992.

This comprehensive review details how 3-6 mg/day iodine enables delta-iodolactone synthesis in thyroid for autoregulation (e.g., Wolff-Chaikoff escape) and in breast tissue for cancer prevention via PPARγ activation and apoptosis. Clinical evidence from 5 mg supplementation trials shows reduced mammary tumor incidence, emphasizing iodolactones’ role beyond thyroid hormone synthesis.

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Some doctors such as Dr. Felice Gersh (see below video)  follow the 1,100 mg of Iodine daily upper limit in the IOM guidelines. I would not say it is wrong to follow the IOM guidelines. Medical practice patterns may vary, based on individual practice style. I think Dr Felice Gersh is a brilliant OB/Gyne doctor and have learned much from her excellent articles and videos, and I agree with her on most controversial medical topics with the exception of this one. Running a medical practice using higher doses of iodine is more work and entails more frequent thyroid lab testing and closer follow-up. This may not appeal to busy doctors who are more focused on other aspects of medical practice.

More iodine isn’t better: The risks of megadosing iodine for women’s health | Felice Gersh, MD

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Header Image: Iodoral, courtesy of Amazon.

Articles with related interest:

Iodine and Bromine Detox With Unrefined Salt

Iodine and Unrefined Sea Salt Part two

Iodine and Hashimotos Thyroid Disease

Iodine at the Health Food Store

Iodine Induced Hyperthyroidism

Iodine Crisis by Lynne Farrow

Iodine is Safe and Effective

Iodine Treats Breast Cancer, Overwhelming Evidence

Iodine and Breast Cancer Prevention

Jeffrey Dach MD
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Published on September 14th, 2025 by Jeffrey Dach MD