I thank Dr. Dach for his comments. Regarding the possibility that iodine supplementation can help prevent breast cancer, an observational study found an inverse association between dietary iodine intake in various parts of the world and the incidence of estrogen-dependent cancers such as breast, endometrial, and ovarian cancer.¹ In contrast, however, in areas of sub-Saharan Africa where iodine deficiency is common, the incidences of these cancers are very low.² If iodine does have a protective effect, it might work by promoting the conversion of estrone and estradiol to estriol, as suggested by Dr. Jonathan Wright. While controlled trials are needed to determine whether iodine supplementation can prevent hormone-dependent cancers (and whether megadoses are needed to achieve such an effect), iodine might be worthwhile for women who have an abnormal “estrogen quotient” (i.e., a low ratio of estriol to [estrone + estradiol]).

However, Dr. Dach’s statement that he has used megadose iodine safely and effectively to prevent breast cancer is difficult to evaluate without further information. His clinical observation of “virtually no breast cancer” over a 5-year period implies that some patients did develop breast cancer. It would be instructive to compare the incidence of breast cancer in his clinic with the incidence in other clinics that use bio-identical hormones, selenium supplements, and (presumably) other nutritional interventions, but which do not use megadose iodine.

Regarding safety issues, I do not know of any scientific evidence that an elevated TSH level in a patient taking megadose iodine is a laboratory artifact. A markedly elevated TSH level combined with a normal free T3 level in an asymptomatic woman is consistent with iodine-induced early thyroid failure, as is the gradual normalization of the TSH level after discontinuation of megadose iodine.

Regarding assessment of iodine status using spot urinary iodine measurements, most experts agree that this method is useful for gathering epidemiological data among populations. However, it is not considered a reliable indicator of iodine status for individual patients, because urinary iodine excretion fluctuates with daily iodine intake and with 24-hour urinary output (which is a function of the degree of hydration).³ To demonstrate that measuring spot urinary iodine is clinically useful in the context of considering megadose iodine supplementation, one would need to show that patients with low values benefit from taking iodine, while patients with normal or high values experience no benefit (or experience harm) from taking iodine.

The possibility that selenium supplementation can prevent iodine-induced autoimmune thyroiditis is intriguing, and is consistent with reports that selenium decreases TPO antibody levels in patients with the spontaneous form of autoimmune thyroiditis.

Alan R. Gaby, MD

Notes

1. Stadel BV. Dietary iodine and risk of breast, endometrial, and ovarian cancer. Lancet. 1976;1:890–891.

2. Edington GM. Dietary iodine and risk of breast, endometrial, and ovarian cancer. Lancet. 1976;1:1413–1414.

3. Gaby AR. Iodine. In: Nutritional Medicine. Concord NH; 2011. www.doctorgaby.com.