In many cases where symptoms of hypothyroidism exist, the cause of the problem may not be the lack of ability to produce an optional amount of thyroid hormone from the thyroid gland. Before initiation of Thyroid Replacement Therapy (TRT), the capacity of the gland to produce the thyroid hormones, primarily T4, should be first determined. Total T4 (TT4) levels should be evaluated to see if they are optimal. If lack of production is determined, then possibly the patient does not have sufficient quantities of the necessary elements required for making thyroid hormone, tyrosine and iodine. Obtaining tyrosine is usually not a problem, as most people get it in their diet. Vegans and vegetarians may lack tyrosine. This might also be the case with body builders who take amino acids supplements, and tyrosine is blocked by competitive absorption with the other amino acids. Iodine deficiency exists in a lot of patients.
If thyroid production is optimal, then one should consider whether there is optimal unbound of free hormone available to work at the receptor. Excessive binding can be commonly caused by oral estrogen therapy, including oral contraceptives. Oral thyroid replacement therapy can also cause excessive binding.
In addition, conversion from the inactive T4 molecule to the active T3 molecule should be considered as a possible source of hypothyroid symptoms. Factors that inhibit the 5’deiodinase enzyme that converts the T4 to T3 include stress or lack of selenium, zinc and a number of other vitamins and minerals.
Even when production, binding, and conversion are not the issue, the free T3 hormone must be properly transported within the cell and the receptors must respond to receive optimal benefit and management of symptoms. Factors which affect transport, receptor density and receptor response include cortisol, ferritin, and Vitamin D. Chronic high or low cortisol decrease thyroid receptor response. Ferritin should be in a range of 90-110 ng/ml and Vitamin D in a range of 60-80 ng/ml to get optimal thyroid response.
Often there are multiple sources of problems causing symptoms of hypothyroidism, and many can be addressed without the need for TRT. If TRT is administered when it is not really needed, the result may be a temporary improvement in symptoms the first few weeks, followed by a return of symptoms. The cause is the body increasing Thyroid Binding Globulin (TBG) in response to the thyroid it doesn’t really need, and therefore binding up hormone it considers excessive. The increase in TBG can take place over 2 to 3 months, so the net effect of any initiation or change in TRT is not really seen immediately.
One more problem that may cause symptoms of hypothyroidism is autoimmune reactions or heavy metal toxicities that damage the cells of the thyroid gland. Autoimmune reactions are the number one cause of all thyroid conditions. Thyroid tests should therefore always include at least one test to check for autoimmune antibodies. These tests include Thyroid Peroxidase antibody (TPO or TPOAb), Thyroglobulin antibody (TgAb), and Thyroid stimulating hormone receptor antibody (TRAb). I prefer to use TPO, as it appears to identify a reaction most commonly. If autoimmune reaction is suspected, all three tests can be ordered. Heavy metal toxicity tests can also be ordered if systemic symptoms indicate.
For more information about hypothyroidism refer to my article Differentiation and Treatment of Hypothyroidism, Functional Hypothyroidism, and Functional Metabolism.