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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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