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Double-Blind Clinical Trials

Does Taking Desiccated Thyroid Cause or Worsen Autoimmune Thyroid Disease?

Fairly often, someone asks me whether taking desiccated thyroid is likely cause or worsen
autoimmune thyroid disease. A few of these people have become concerned because of a rabbit study they’ve heard about. I’ve read summaries of this study, and typically the summaries state: “Rabbits developed autoimmune thyroid disease after being injected with thyroid extract from other rabbits.”

After reading these summaries, some people understandably asked, “The rabbit developed
autoimmune thyroid disease after being exposed to thyroid extract. Doesn’t this mean that if I expose myself to thyroid extract in desiccated thyroid, it can cause me autoimmune thyroid disease in me? Some people who already had high thyroglobulin or peroxidase antibodies asked, isn’t desiccated thyroid likely to stoked up these antibodies in me?

In the studies these people mention, the researchers did inject rabbits with extracts of rabbit thyroid glands. And the injections led to anti-thyroid antibodies in the injected rabbits and damage to their thyroid glands.

However, the injections also included saline (salt) and another substance called “Freund’s
adjuvant.”[4,p.1295] The importance of this latter ingredient is that it’s a powerful booster of the immune response to antigenic stimuli. Laboratory researchers use it to augment antibody responses to antigens that might otherwise provoke only faint antibody reactions. The adjuvant is severely toxic. Researchers are banned from using it in humans, and they use it sparingly in laboratory animals.

Because the rabbit thyroid extract was mixed with saline and Freund’s adjuvant, I’m curious as to whether the injected thyroid extracts alone would have provoked antibodies against thyroglobulin. Maybe it would not have.

However, there’s also another important consideration. I’ve talked with people from the
companies that manufacture desiccated thyroid products, and they’ve told me that they don’t measure the amount of the proteins thyroglobulin and peroxidase in the thyroid powder they use in their products.

Nonetheless, the important point is that the thyroglobulin and peroxidase in desiccated thyroid are proteins. Ingesting these proteins may not increase antibody activity for this
reason protein-digesting enzymes in the GI tract are likely to decompose the proteins into amino acids. And although the amino acids may then absorb into the body, they aren’t likely to recompose themselves into proteins that function as antigens to stoke up antibody reactions against them.

I know of only one study in which researchers actually tested the hypothesis that desiccated thyroid might affect patients’ autoimmune thyroid disease. The researchers switched patients with the disease from synthetic T4 to desiccated thyroid for a year. Other patients continued to use synthetic T4. At the end of the year, the two groups of patients did not differ in measures of autoimmune thyroid disease; desiccated thyroid had not worsened any immune measures.[5]

To answer this oft asked question, then, ingesting desiccated thyroid is not likely to cause or worsen autoimmune thyroiditis.

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