Some 6 million people in the United States suffer from Bipolar Disorder. Research indicates that genetic factors account for about 80% of it. It is widely believed to be incurable and lifelong, able to be managed only with antipsychotic medications.

But it may have a surprising cause.

Iodine and Bipolar Disorder

While the exact genetic connections are poorly understood, this study indicates that the genetic mutation responsible may be a particular deiodinase enzyme, functional in the prefrontal cortex. Deiodinase is the enzyme that converts the thyroid hormone T4, which represents only about 20% of your active thyroid functioning, to the 80% active T3, by removing an iodine molecule. If deiodinase functions poorly, you end up with a surplus of T4, which is not nearly as useful as T3.

This means you may be functionally hypothyroid, even if you’re technically in range on labs. According to this study, subclinical hypothyroidism is even more common than overt hypothyroidism in bipolar disorder.

One of the classic treatments for hyperthyroidism is lithium, and its mechanism of action for treating bipolar disorder is likewise poorly understood. If bipolar can be due to hypothyroidism, a drug which classically suppresses the thyroid seems an unlikely solution. But while lithium does suppress many aspects of thyroid function, it does one thing that might be the key to its efficacy: it enhances the effect of the particular deiodinase enzyme which converts T4 to T3 in the prefrontal cortex. (The prefrontal cortex is the portion of the brain most active in decision making and executive function.) 

This supports the study above, that perhaps the genetic cause of bipolar is the malfunction of that particular enzyme.

Your Thyroid, Endocrine Disruptors, and Bipolar Disorder

While thyroid disease in general is strongly correlated with bipolar (particularly subclinical, as mentioned above), Hashimoto’s Thyroiditis (or autoimmune destruction of the thyroid) is also strongly correlated.

Another piece of the puzzle: while most thyroid hormone is transported by Thyroxine Binding Globulin (TBG), in the Central Nervous System (CNS) T4 is also transported by another protein, called transthyretin (also known as prealbumin). Low or damaged transthyretin has also been linked to bipolar disorder as well as to depression—probably because low transthyretin means less T4, which means less T3 in the brain as well.

What can damage transthyretin? Well, PCBs, for one: these highly ubiquitous pesticides bind to the thyroxine receptors in transthyretin, along with phthalates from plastics, PBDEs, and other solvents. 

Interaction of the Thyroid and the Adrenals

In my experience, treating the thyroid is often very helpful and sometimes a game-changer for bipolar patients. But they usually also require adrenal balancing. This is probably because high levels of cortisol, the body’s stress hormone, will also decrease the conversion of T4 to T3. (When you’re stressed out, the body is trying to put on the brakes to get you to slow down so they can recover.)

The Upshot

If you or someone you love suffers from bipolar disorder, ask your doctor for a full thyroid workup, including fT4 and fT3 and thyroid antibodies (anti-TPO and anti-thyroglobulin). If you are at the lower end of the reference range, even if you are within normal limits, consider discussing treatment on a trial basis, going very slow with dosing to keep from overshooting.

I also highly recommend a salivary cortisol test to determine adrenal function, and appropriate treatment if cortisol levels are too high or too low.

Consider testing for solvents which may compromise your transthyretin, especially if you know you’ve had a major chemical exposure.

Many of my bipolar patients also benefit greatly from neurotransmitter testing and appropriate balancing, and sex hormone balancing—but I’d start with the thyroid and the adrenals first.