Many people with hypothyroid conditions, including Hashimoto’s Thyroiditis, take either synthetic or natural thyroid hormone. But many of these people have no idea why thyroid hormone is important. Sure, most people realize that thyroid hormone is important in regulating the metabolism of the body, which is why low thyroid hormone levels frequently lead to symptoms such as fatigue, weight gain, and constipation. But thyroid hormone has many other important roles in the body, and it is extremely important in the growth, development, and metabolic function of just about all of the organ systems and tissues of the body (1) .
Here are some of the more important functions of thyroid hormone:
Protein, Carbohydrate, and Lipid Metabolism. Thyroid hormone plays an important role in the metabolism of protein, carbohydrates, and fats. With regards to protein, thyroid hormones stimulate the synthesis as well as the degradation of proteins (2) . As a result, a deficiency in thyroid hormone can affect protein synthesis, which of course is very important. Thyroid hormone also plays a role in carbohydrate metabolism (3) . Thyroid hormones affect the synthesis, mobilization, and degradation of fats (4) . Severe hypothyroidism is usually associated with an increased serum concentration of total cholesterol and atherogenic lipoproteins.
Gene Expression. Thyroid hormone plays an important role in regulating the expression of genes. It does this through thyroid hormone receptors, which are DNA-binding transcription factors that function can activate or repress gene transcription (5) .
Brain Development. Thyroid hormone plays an important role in brain development and function. Triiodothyronine (T3) is the active form of thyroid hormone, and controls the expression of genes involved in myelination, cell differentiation, migration, and signaling (6) . This is one of the reasons why a deficiency of thyroid hormone can cause cognitive problems.
While many different factors can affect thyroid function, I came across an interesting study which discussed how certain environmental contaminants can disrupt thyroid function, thus affecting brain development (7) . The study showed that both polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) are prevalent environmental contaminants that disrupt thyroid hormone signaling at the receptor level, and can cause problems with brain function.
Peripheral Nerve Regeneration. T3 plays a role in peripheral nerve regeneration (8) . Schwann cells are located in the peripheral nervous system, and they produce the myelin sheath around the axons of the neurons. The myelin sheath offers protection to the neuron, and also plays a role in nerve conduction. When it comes to peripheral nerve regeneration, it seems T3 helps with the formation of the myelin sheath, probably by directly stimulating the Schwann cells (8) .
Reproductive Health. Having normal thyroid function is important for reproduction. Male reproduction is adversely affected by both thyrotoxicosis and hypothyroidism (9) . Hyperthyroidism can lead to erectile abnormalities and sperm motility, whereas hypothyroidism is associated with oligomenorrhea (9) . However, hypothyroidism can also lead to prolonged, heavy menstruation (10) . Thyroid dysfunction reduces the likelihood of pregnancy and adversely affects pregnancy outcome (11) .
Bone Health. Thyroid hormones are required for skeletal development and establishment of peak bone mass (12) . In adults, T3 regulates bone turnover and bone mineral density, and normal euthyroid status is essential to maintain optimal bone strength (12) . Hypothyroidism causes impaired bone formation and growth retardation whereas hyperthyroidism results in accelerated growth, advanced bone age, and decreased bone mass (13) . Population studies indicate that hypothyroidism and hyperthyroidism are both associated with an increased risk of fracture (12) .
Wound Healing. Thyroid hormone may play an important role in wound healing (14) . As a result, someone with a hypothyroid condition might experience slower healing when experiencing a cutaneous wound.
So hopefully you now realize how important thyroid hormone is. When dealing with people who have hypothyroid conditions, my goal is to attempt to restore their thyroid health so they won’t need to rely on taking synthetic or natural thyroid hormone. However, while I’m trying to accomplish this some people to need to take an exogenous source of thyroid hormone. And some people do need to take thyroid hormone on a permanent basis. If the thyroid hormone levels are depressed, or even if they are within the reference range but are very low, due to the importance of thyroid hormone it might be necessary to take something such as Levothyroxin, or a natural form like Armour or Nature-Throid.