What role does iodine intake play in breast cancer?

Research shows that a good iodine intake has a protective effect against fibrocystic breast diseases like cancer. But its organic form wins over salt.

Prevention is better than therapy

When iodine levels fall, iodine receptors are blocked by increased fluoride, chloride and bromide concentrations in water, food and the environment, which promotes the development of breast cancer and other types of tumours.1,2

In areas where both selenium and iodine intake are high (e.g. Japan), the risk of breast cancer is lower than in areas with high selenium and low iodine intake (e.g. United States) or in areas where both are low (e.g. Northern Europe).3

Can iodine supplements reverse fibrocystic breast changes?

Glandular tissues require iodine for proper development and function. Breast tissue has a high concentration of iodine, especially during pregnancy and breastfeeding.4 In women of reproductive age (or on oestrogen replacement therapy during the menopause), fibrocystic breast disease has become more common as a benign condition in recent decades. It is associated with nodular, pain-sensitive breasts (especially towards the end of the cycle) and palpable fibrosis. Clinical studies indicate an improvement in fibrocystic breast disease and cyclic mastalgia after supplementation with molecular iodine (I2).2,4,5

This last point is important: there is a specific form of iodine that affects breast tissue and that is elemental (unbound) iodine, i.e. I2 - not iodide, which is an iodised salt (such as potassium iodide).6 This is the preferred form of iodine for the thyroid gland.7

In studies, iodine deficiency also caused mammary atypia and dysplasia in laboratory animals (rats), which were reversed by iodine supplementation. Iodine also has antioxidant and antiproliferative effects and stimulates apoptosis in breast tissue.2,3

Does iodine reduce the risk of breast cancer and have an anti-proliferative effect?

Slim women with fibrous, dense breast tissue belong to the risk groups for breast cancer. The population-based long-term study 'Malmö Diet and Cancer Study' provided pre-diagnostic blood samples from 1,159 breast cancer patients and 1,136 controls, in which the initial levels of iodine and selenium in the serum were recorded. Here, too, the combination of high iodine and selenium levels was associated with a lower risk of breast cancer.3

Iodine is also involved in the regulation of cell growth and cell division and, together with fatty acids (so-called "iodine lactones"), is involved in the initiation of apoptosis in pathological cells.7 A cytostatic effect has been described on cancer cells without damaging healthy cells.5 The results of some studies indicate that it is again molecular iodine that significantly inhibits cell growth in breast cancer as well as in other types of cancer.6,8 For example, adjuvant iodine (I2) supplementation in combination with doxorubixin led to a reduction in tumour size and PCNA expression (a marker for proliferation activity in breast cancer).2,9

The addition of iodine (I2) to standard breast cancer treatment regimens (FEC/TE) resulted in an improved response when used preoperatively or in conjunction with conventional chemotherapy to shrink the cancer prior to surgery (30 patients with stage II and 30 patients with stage III breast cancer).10 The 5-year disease-free survival (DFS) rate was significantly higher in patients treated with the iodine add-on before and after surgery than in those who received the add-on only after surgery (82% vs. 46%). Oral supplementation with iodine was associated with a significant attenuation of side effects and the absence of chemoresistance (typically 30% among the treatment regimens used).

"Tumours treated with iodine showed a lower invasive potential and a significant increase in apoptosis, oestrogen receptor expression and immune cell infiltration," the study authors concluded.10 A larger Phase III trial on the efficacy of chemotherapy + iodine treatment in advanced breast cancer was subsequently planned.

Where is iodine found?

Many people use iodised table salt with the idea of improving their iodine intake - but the usual household quantities provide far too little iodine.7 Moreover, the added iodine is as good as gone within two weeks of opening a packet of salt. Furthermore, many valuable ingredients that are naturally contained in good rock or sea salt, for example, are lost in the refining process and artificially added minerals, including iodine, do not have the same value for the body. In addition, harmful additives are often added to highly processed salts, for example to prevent clumping (anti-caking agents). A good iodine-containing brine would be more recommendable here.

Seaweed (such as kelp, nori, kombu and, to a lesser extent, wakame) is one of the best food sources of iodine, as are sea fish and shellfish. Eggs, milk or Greek yoghurt, for example, contain significantly less iodine, but still a reasonable amount. If you don't like eating seaweed, you can also buy it in the form of granules and sprinkle it into soups or other dishes. Standardised preparations made from residue-controlled seaweed to prevent iodine deficiency disorders (daily intake of around 300 μg iodine) are also often recommended.7 Iodine is also contained in human breast milk.4

If mastopathy or breast cancer is already present, significantly higher doses than the preventive doses (in the milligram range) are often used. Such therapy with elemental iodine (e.g. as a 5 mg preparation or also contained in "Lugol's iodine" solution, which is a combination of iodide and 5% iodine) should only be carried out on the orders of a doctor who is familiar with iodine therapy and is able to monitor thyroid function.4 Overall, this is an exciting field in which further research is needed.

  1. Molecular Iodine and Breast Cancer: What you must know. Oncoplus Hospital https://www.oncoplus.co.in/molecular-iodine-and-breast-cancer-what-you-must-know/ (2020).
  2. Rappaport, J. Changes in Dietary Iodine Explains Increasing Incidence of Breast Cancer with Distant Involvement in Young Women. J Cancer 8, 174–177 (2017).
  3. Manjer, J., Sandsveden, M. & Borgquist, S. Serum Iodine and Breast Cancer Risk: A Prospective Nested Case–Control Study Stratified for Selenium Levels. Cancer Epidemiology, Biomarkers & Prevention 29, 1335–1340 (2020).
  4. Office of Dietary Supplements - Iodine. https://ods.od.nih.gov/factsheets/Iodine-HealthProfessional/ (2023).
  5. Rösner, H., Möller, W., Groebner, S. & Torremante, P. Antiproliferative/cytotoxic effects of molecular iodine, povidone-iodine and Lugol’s solution in different human carcinoma cell lines. Oncol Lett 12, 2159–2162 (2016).
  6. Dr. Laurie Marzell N.D., N.C.M.P. Healthy Breasts: The Role of Iodine in Breast Cancer Prevention | Showit Starter Blog. https://drmarzell.com/healthy-breasts-the-role-of-iodine-in-breast-cancer-prevention/
  7. [In German only] Jod und Brustkrebs. biokrebs.de/images/download/Kurzinfos/Jod_und_Brustkrebs.pdf.
  8. Soriano, O. et al. Antineoplastic effect of iodine and iodide in dimethylbenz[a]anthracene-induced mammary tumors: association between lactoperoxidase and estrogen-adduct production. Endocrine-Related Cancer 18, 529–539 (2011).
  9. Alfaro, Y., Delgado, G., Cárabez, A., Anguiano, B. & Aceves, C. Iodine and doxorubicin, a good combination for mammary cancer treatment: antineoplastic adjuvancy, chemoresistance inhibition, and cardioprotection. Mol Cancer 12, 45 (2013).
  10. Moreno-Vega, A. et al. Adjuvant Effect of Molecular Iodine in Conventional Chemotherapy for Breast Cancer. Randomized Pilot Study. Nutrients 11, 1623 (2019).