The thyroid gland is an endocrine gland located in the front of our necks. It stores and produces hormones that affect the function of virtually every organ in our bodies. Thyroid hormone (Triiodothyronine or T3) regulates our metabolic rate and is associated with modest changes in body weight and energy levels. Major targets of thyroid hormone are the skeleton, the heart and the metabolic machinery of every cell.
The cornerstone of clinical assessment of thyroid status is measurement of serum TSH, or thyroid stimulating hormone. TSH acts on the thyroid gland itself, stimulating increased production and secretion of T4 (i.e. Thyroxine) and T3, both of which are thyroid hormones.
Abnormally high and low levels of thyroid hormones can trigger symptoms in previously asymptomatic individuals. Abnormally high levels – hyperthyroidism – can produce a rapid heart rate and eyes that appear to be bulging. Grave’s disease is the most common cause of hyperthyroidism in countries with sufficient iodine intake. Grave’s disease is an autoimmune condition, which means that the body’s own immune system injures the thyroid gland.
Abnormally low levels – hypothyroidism – can result in fatigue, constipation, dry skin and coarse hair. The most common cause of hypothyroidism is an autoimmune process known as Hashimoto’s thyroiditis.
Agents that have been shown to interfere with the action of thyroid hormone include cigarettes, as well as a range of environmental agents, especially polychlorinated biphenyls (PCBs). Individuals with other autoimmune diseases, like celiac disease, also have a higher risk of autoimmune thyroid disease.
Soy is frequently accused of being a thyroid antagonist, but there is no convincing evidence that soy protein or isoflavones interfere with the action of thyroid hormone in humans. Soy protein, however, can interfere with T4 absorption from the intestine. This is important for infants with congenital hypothyroidism on T4 replacement and receiving soy-based formula. It’s also important for individuals diagnosed with hypothyroidism and taking supplemental thyroid hormone.
– Jamie Corroon, ND, naturopathic physician and resident at Bastyr Center for Natural Health, the teaching clinic of Bastyr University.