The Most Accurate Measurement of Whole-Body Iodine Status

In reviewing the article in your January 2013 magazine, “Evaluation of the Iodine Loading Test: Urine Iodine Excretion Kinetics after Consumption of 50 mg Iodine/Iodide” by Theodore Zava of ZRT Laboratories several points need clarification.

The goal of the iodine project, initiated by Guy Abraham, MD, was to investigate the role of iodine in human health and to propose a systematic approach to evaluate iodine supplementation. The idea of whole-body iodine sufficiency was a new concept that recognized that iodine is necessary for not only the thyroid gland but many other body systems.

When Mr. Zava compares the de Benoist findings of 89% iodine sufficiency in the US with data showing iodine deficiency reported to be greater than 90%, he is comparing two completely different measures of iodine status. De Benoist is simply looking at minimal iodine levels that will prevent goiter not whole-body iodine sufficiency.

We do not believe that this presents confusion when one understands the difference in the two protocols. We are in agreement with the WHO that small microgram amounts of iodine are adequate to prevent goiter in the vast majority of the population. However, iodine has many other uses in the body, including maintaining the normal architecture of all the glandular tissues including the breast, ovary, and uterus.

The traditional spot iodine test is a useful tool that can be used to estimate whether iodine intake is adequate. However, this test provides no useful information on iodine status after iodine therapy has been instituted. That is why the 24-hour loading test was developed – it provides a measurement of whole-body iodine status. Zava states, “…if iodine supplementation is not discontinued for several days before testing, residual supplemental iodine will be excreted along with the 50 mg loading dose, giving a test result showing a false high excretion.” He is correct. We wish Mr. Zava had called any of the four major laboratories that currently offer the iodine loading test – FFP Laboratory, Labrix, Doctor’s Data, and Hakala Research – since they all recommend stopping iodine supplementation 48 hours before starting the test.

Zava recommends extending the collection period past 24 hours. This is impractical and unnecessary. As discussed by Drs. Abraham and Brownstein, the iodine loading test evolved from testing subjects who ingested varying milligram (12.5–50 mg) amounts of iodine and then collecting 24 hours of urine. The subjects who had the best clinical responses achieved 90% or more iodine excretion after following the iodine loading test parameters. Although the 90% excretion level was chosen arbitrarily, it appears to give the best clinical results.

Zava recommends doing 24-hour fecal testing of iodine levels. Again, this is impractical and unnecessary. Fecal iodine excretion levels amount to approximately 2% (Williams Textbook of Endocrinology. 9th ed. 1998:392). Fecal excretion of 2% has been confirmed on a patient taking 100 mg of Iodoral daily (data on file, Hakala Research).

One final note. Although spot urine or salivary iodine testing provides useful information on individual and population iodine intake, it provides no information on whole-body iodine status. In fact, our (DB and JF) clinical experiences, after testing thousands of patients with it, have shown that it does not correlate clinically after patients begin ingesting milligram amounts of iodine. To date, we feel that the iodine loading test is the most accurate measurement of whole-body iodine status.

David Brownstein, MD

Jorges Flechas, MD

Charles Hakala, RPh