There are two main antibodies involved in Hashimoto’s: anti-thyroid peroxidase (TPO) and anti-thyroglobulin. The elevation of these antibodies mean that the immune system is attacking and destroying two of the necessary components of thyroid hormone.
Thyroglobulin is a precursor for thyroxine (T4), the primary hormone produced in the thyroid gland. So attacking this means you end up with less T4, and are hypothyroid.
TPO is a little more complex. Let’s first back up a bit.
Quick Biochemistry Interlude: What Thyroid Peroxidase (TPO) Does
Thyroxine is a tyrosine molecule (an amino acid) with four iodine molecules attached to it. Iodine is one of the halides in chemistry: by itself, it exists as iodide, an ion with a single negative charge. It needs one more electron to be electrically neutral; for this reason, two iodide ions generally combine to form an iodine molecule.
TPO catalyzes this process of converting iodide ions to iodine molecules (necessary components of thyroxine). Once produced, these iodine molecules can be attached to a tyrosine to form thyroxine.
Enter Hydrogen Peroxide (H2O2)
But their creation releases hydrogen peroxide, a powerful pro-oxidant (opposite an antioxidant). Pro-oxidants are a problem if you can’t neutralize them. Fortunately the body has a great system to deal with H2O2: it’s glutathione, the body’s most powerful antioxidant. Glutathione, together with selenium, helps to convert H2O2 to H2O (water).
So as long as you don’t have an overabundance of H2O2, and you have plenty of selenium, you’re fine.
But if antibodies attack TPO, you cannot form iodine from iodide very efficiently. This is why giving iodine to someone with Hashimoto’s can cause the condition to flare: iodide to iodine conversion is already slow, and you’re giving more work to a backed up system, producing more H2O2 than the system can handle, triggering thyroid damage and destruction.
If you have Hashimoto’s and you’re also low in iodine (on a serum iodine test), it’s important to make sure you’re cautious with your iodine intake (I generally don’t put these patients on more than 200 mcg) AND you’re counter-balancing it with adequate selenium (200 mcg is a minimum for all my Hashimoto’s patients whether on iodine or not, and I will increase this if they are).