The thyroid gland, located in the neck, produces a variety of thyroid hormones. These regulate virtually every aspect of metabolism: body temperature, mood, sex hormones, energy levels, and even impact one’s appearance, from hair and nails to skin and waistline. Less understood about thyroid hormones is that there are two basic types – T3 and T4 (so named for the number of iodine molecules each has) – and they serve different biological functions. T4, which is made in the thyroid gland, serves as the precursor hormone to T3. It is entirely possible, even common, for the thyroid gland to produce plenty of thyroid hormone in the form of T4, but not be converted into T3. Because T3 is the more biologically potent thyroid hormone and acts directly on bodily tissues, one may exhibit signs of hypothyroidism (fatigue, weight gain, feeling cold, thinning hair, mood swings, etc) even when T4 is in the normal range.
It is worth noting that the conversion of precursor thyroid hormone T4 into active thyroid hormone T3 occurs outside the thyroid gland, mostly in the liver and kidneys. This conversion into active thyroid hormone occurs through the action of enzymes that are dependent on the mineral selenium (these enzymes are called deiodinases because they remove aniodine in T4 to convert it to T3). Therefore, a selenium deficiency can cause a person to be low in active thyroid hormone, even if their thyroid gland is producing plenty of precursor thyroid hormone. To complicate things, TSH (thyroid stimulating hormone) is often found to be “normal” despite poor thyroid conversion. In essence, a reliance on simple thyroid tests may suggest a person is not hypothyroid when in fact they are hypothyroid due to a selenium deficiency. Both low zinc and antioxidant status can also impair the conversion of T4 (precursor) to T3 (active) hormone. The most concentrated dietary source of selenium is the Brazil nut, because the soil where Brazil nuts are grown is particularly rich in selenium.
Find out whether you have a selenium deficiency today!