The connection between iodine and Hashimoto’s disease has been one of the most requested topics that I cover, so I’d like to present the research on this topic, so we can set the record straight. Please be aware that none of this is my opinion but rather a detailed analysis of what the scientific literature currently presents.

Your body has about 15 to 20 mg of iodine and 70 to 80% of it resides in the thyroid gland. Iodine is transported into the thyroid gland through the sodium-iodine symporter or NIS. The thyroid peroxidase enzyme oxidizes iodine which is then integrated into thyroglobulin resulting in the production of thyroxine (T4) and triiodothyronine (T3). Thyroid stimulating hormone (TSH) regulates this process.

Your thyroid only needs 150 to 250 micrograms a day of iodine to function properly. Once iodine intake exceeds this range, hypothyroidism and autoimmune thyroid disease may occur in some individuals.

How Much Iodine do the Japanese Consume?

The first issue I want to briefly clear up is the false idea that the Japanese consume 13.8 mg of iodine per day from their diet. This is actually a mischaracterization of a single study by Nagataki et al that I will clarify. Here is what the literature shows:

Aceves et al state that, “This element (iodine) has been associated with the low incidence of benign and malignant breast disease in Japanese women (iodine average consumption in the Japanese population is 5,280 μg/day versus 166-209 μg/day in the UK and USA, respectively).” 5,280 ug/day equals 5.28 mg/day.

Cann et al agree in their paper stating, “Japan has a comparatively high iodine intake with an average urinary iodine concentration of 3400 μg/L (approximately 5,280 μg/day) as determined in a recent study of 4138 men and women in Sapporo, Japan.”

Tajiri et al state that, “...the average daily iodine intake was 1-5 mg in the remaining 10 patients, equivalent to the ordinary intake of normal Japanese.”

Kapil et al state, “Iodine Intake in Japan: Average daily intake of iodine in Japan has been reported to be 3000 micrograms, which is 20 times more than the RDA value of 150 mcg in India.”

According to a report on iodine from the FAO/WHO Expert Consultation on Human Vitamin and Mineral Requirements, the following is stated about the daily iodine intake in Japan: “The amount of iodine intake by the Japanese is in the range of 2-3 mg/day.”

And finally, let’s clarify the Nagataki study. Nagataki states, “...the dry weight of such food as ‘tangle’(Laminaria) contains 0.3% iodine...” “...the average daily intake of seaweed was 4.6 g (wet weight).”  The well-known doctors who make this claim of 13.8 mg made a major mathematical error. 0.3% of 4.6 g does in fact equal 13.8 mg, but they confused dry weight and wet weight. The issue is that the paper is referring to dry weight in the above quote but the second quote refers to wet weight.

A follow-up