Thyroid testing identifies the levels of several hormones, including T4 and T3, which are the most active of the thyroid hormones; and thyroid-stimulating hormone, produced by the pituitary gland that controls the production and secretion of thyroxine. When T3 and T4 levels rise, the pituitary secretes less TSH, which causes production ofT3 and T4 to decline, restoring balance. If T3 and T4 levels fall, secretion of TSH again increases, which boosts production ofT3 and T4.
Testing for T3, T4, and TSH levels is a good start if you have symptoms of hypo- or hyperthyroidism, but because the normal range for these blood tests is wide, it’s possible to have thyroid dysfunction with so-called normal test results. Measurement of thyroid antibodies can provide additional information about the risk of depression and treatment prognosis. One report, for example, found that women with high levels of antithyroid peroxidase (anti-TPO) antibodies are more likely to become depressed than those without these antibodies. A subsequent study concluded that testing for antibody levels “seems necessary,” especially in the elderly and in individuals who do not respond to depression treatment
While women are more likely to have thyroid hormone imbalance (especially hypothyroidism) than men are, a subgroup of women are at particular risk. Up to 10 percent of new mothers develop postpartum thyroiditis, chronic inflammation of the thyroid gland, and concurrent depression. This condition can be diagnosed with tests that check for antibodies against the thyroid. Research has shown that up to 50 percent of women who have high levels of thyroid antibodies during their first trimester develop postpartum thyroiditis and are subsequently at risk for postpartum depression. These women may be iodine-insufficient and will probably respond to iodine supplementation. Women who are significantly iodine insufficient and then become pregnant will become much more insufficient, because iodine is preferentially transported to the fetus. As the woman becomes more insufficient, she is likely to develop anti thyroid antibodies, and after delivery is more likely to develop postpartum depression.
In recent years, studies of depression have shown that some people who take antidepressants respond better if they also take T3. In one particular study of patients who had hypothyroidism, those who took a combination ofT3 and T4 had better results in regard to mental and emotional symptoms than those who took T4 alone. Unfortunately, most patients with hypothyroidism who are treated conventionally usually take only T4. Occasionally patients are given T3 (as the medication Cytomel), which must be taken several times a day and can cause mood and energy swings. To prevent these problems, a physician could prescribe long-acting T3, which is available from compounding pharmacies. Today, however, I would certainly try therapeutic doses of iodine before prescribing long-acting T3.