Most doctors will run labs for TSH only, or occasionally T4. Elevated TSH means that the thyroid isn’t responding to the signal from the pituitary, so the pituitary effectively “shouts louder.” An unresponsive thyroid might be due to:
- Lack of available building blocks (iodine, tyrosine, selenium, zinc, etc), or lack of necessary nutritional cofactors to turn them into active hormone. This is more likely the case if the diet is especially poor, or there’s some other malabsorption syndrome present. But it can also happen as a result of halogen exposure in the water supply, as well as in baking products. Halogens are other atoms on the periodic table directly above iodine: fluorine, chlorine, and bromine. These atoms are chemically similar to iodine, so they compete with iodine for absorption into the thyroid. When other halogens replace iodine, thyroid hormone cannot work properly. Fluorine and chlorine are commonly added to the water supply, while brominated compounds are commonly used in commercial bread and baking products.
- Antibodies. Hashimoto’s, or antibodies against the thyroid, is a very common cause of hypothyroidism. Autoimmunity in general has its own set of causality. However, production of thyroid hormone creates oxidative stress, which requires selenium for clean-up. Without this clean-up, autoimmunity can set in. So selenium deficiency may be one risk factor.
- Mercury toxicity. Heavy metals in general are bad news, but mercury particularly can antagonize selenium, which is necessary for multiple steps of thyroid hormone production. For more on heavy metal toxicity, read on.
- Drug Suppression. Amiodarone and lithium are two well-documented examples of thyroid suppressing drugs.
It is possible for TSH and total T4 to both be normal, while patients are still functionally hypothyroid. This may be due to:
- Higher circulating TBG (thyroxine-binding globulin). T4 and T3 hormones that are bound to TBG are not available to stimulate receptors. This is a good reason to test free T4 and free T3, not just the total amounts of both. One possible cause for high TBG is estrogen dominance, which can also cause a host of female hormonal problems.
- A sluggish liver. About 60% of your T4 gets converted to T3 in your liver… a process requiring selenium (again) and magnesium. If your liver is backed up (and one way to tell is if you have had a history of toxic exposure, and if you are chemically sensitivity now), this might not happen efficiently.
- Higher conversion of T4 to rT3 (reverse T3, which is inactive), instead of active T3. Your liver converts some T4 to rT3 when it has too much of the former, and this is a normal process. However, in times of high stress (read: high circulating cortisol), your body is in crisis mode. This means it needs to conserve energy to deal with the stressor, so things like growth and metabolism become a lot less important. If you’re chronically stressed out all the time, this process might be ongoing (and it might also lead to leptin resistance, for patients who can’t lose weight).
I prefer to treat hypothyroidism with NatureThroid or Armour (glandular products containing T1, T2, T3, T4, and calcitonin, as well as the building blocks to repair the thyroid), since in my experience, patients do much better on those than on Synthroid (T4 only). Then, we investigate and treat some of the other possible causes mentioned above.