As an essential nutrient, iodine is needed for thyroid function, and a deficiency is linked to higher risk of thyroid and stomach cancers. Some evidence shows that treatment with molecular iodine before breast cancer surgery may improve tumor response and reduce some side effects.
Safety and precautions
Cancer risk
“Excess iodine intake may be an unfavorable factor in breast cancer.”1He S, Wang B et al. Iodine stimulates estrogen receptor singling and its systemic level is increased in surgical patients due to topical absorption. Oncotarget. 2017 Sep 4;9(1):375-384. See also a discussion of modes of action of iodine on breast cancer in Are you a health professional? ›
Some evidence also links high levels of iodine in urine to higher levels of thyroid cancer, although the authors of a large study concluded that high urinary iodine is a specific characteristic of papillary thyroid cancer but not a cause. In this analysis, cancer risk was not related to regional iodine intake.2Yan AR, Zhang X et al. Urinary iodine is increased in papillary thyroid carcinoma but is not altered by regional population iodine intake status: a meta-analysis and implications. Endocrine Journal. 2019;66(6):497-514. Higher levels of iodine in the diet were linked to higher incidence of thyroid cancer in the area around Lahore, Pakistan, but only among rural residents and not urban residents. The authors did not report the comparative intake of iodine between rural and urban areas or the proportions of people who may have iodine deficiency or excess in either area. We know only that dietary levels of iodine that are too high are linked to higher risk of thyroid cancer, but this study does not tell us what level is “too high.”3Asif F, Noor-Ul-Amin M, Jabeen R. Identification of thyroid cancer risk factors incidence in urban and rural areas, Pakistan. Pakistan Journal of Pharmaceutical Sciences. 2020;33(6):2607-2610.
The antiseptic use of iodine during breast surgery leads to significantly higher urinary iodine levels for about two days among people undergoing breast surgery compared to other people, although any connection to cancer risk was not investigated.4He S, Wang B et al. Iodine stimulates estrogen receptor singling and its systemic level is increased in surgical patients due to topical absorption. Oncotarget. 2017 Sep 4;9(1):375-384.
Urinary iodine concentration did not show a link to the prevalence of BRAFV600E mutation, which is related to several types of cancer in a large study.5Lin YY, Hsieh YS. Iodine nutritional status is not a direct factor in the prevalence of the BRAFV600E mutation in papillary thyroid cancer. Archives of Endocrinology and Metabolism. 2023;67(2):172-178.
Also see evidence of higher risk of thyroid cancer among people with an iodine deficiency in How can iodine help you? What the research says ›
Side effects
High intake of iodine can cause health risks related to the thyroid gland:6Office of Dietary Supplements. Iodine Fact Sheet for Health Professionals. National Institutes of Health. May 1, 2020. Viewed May 6, 2020.
- Hyperthyroidism
- Goiter
- Thyroiditis
- Thyroid cancer
Some people are intolerant of, or sensitive to, iodine in chemical agents such as radiocontrast agents used for x-rays, in iodine-containing disinfectants like Betadine, or even in foods. If you suspect you have an iodine allergy, you can ask your doctor for diagnostic tests. Anyone with an allergy or sensitivity should make sure that all their medical professionals are aware of an iodine allergy before medical treatment.7Cadman B. What is an iodine intolerance? Medical News Today. April 3, 2018. Viewed May 6, 2020.
Overdose can result in acute poisoning symptoms:8Office of Dietary Supplements. Iodine Fact Sheet for Health Professionals. National Institutes of Health. May 1, 2020. Viewed May 6, 2020.
- Burning of the mouth, throat, and stomach
- Fever
- Abdominal pain
- Nausea
- Vomiting
- Diarrhea
- Weak pulse
- Coma
People with autoimmune thyroid disease and iodine deficiency may be more susceptible to overdose and may have side effects even when taking iodine doses considered safe for the general population.9Office of Dietary Supplements. Iodine Fact Sheet for Health Professionals. National Institutes of Health. May 1, 2020. Viewed May 6, 2020.
Interactions with medications
Iodine can interact with many medications. Before taking an iodine supplement, consult your physician regarding safe use. Consult your pharmacist to check for any medications or supplements that may interact with iodine.
Helpful link
Patrick L. Iodine: deficiency and therapeutic considerations. Alternative Medicine Review. 2008 Jun;13(2):116-27.
References