Selenium's Vital Role in Thyroid Hormone Function

By Byron J. Richards, Board Certified Clinical Nutritionist

October 14, 2013

Selenium's Vital Role in Thyroid Hormone Function
This is a very straightforward issue. If you desire your thyroid to work properly and thyroid hormone to work correctly in your body it is vital that you have adequate selenium intake, otherwise your thyroid will operate in a state of stress. This opens the door for all manner of metabolic problems.

While nutrients like iodine and tyrosine are needed for the actual structure of thyroid hormone, selenium is involved with the management of thyroid hormone. In reality a great many nutrients are needed for thyroid hormone production and regulation. However, the case can be made that none is more important than selenium.

Selenium Within the Thyroid Gland

The highest concentrations of selenium in the human body are in the liver, kidneys, and thyroid gland. Within the thyroid gland selenium is essential for the production of thyroid hormone. Cells within your thyroid gland, called thyrocytes produce a protein called thyroglobulin. It is thyroglobulin's job to connect iodine and tyrosine to form basic thyroid hormone (thyroxine or T4). As it turns out tremendous amounts of free radicals are generated during this process in the form of hydrogen peroxide (H2O2). If these free radicals are not deactivated then damage to the thyroid gland occurs and the efficiency of the needed production of thyroid hormone is disrupted.

To deal with this problem your thyrocytes make an antioxidant enzyme called glutathione peroxidase, which requires selenium. Glutathione peroxidase deactivates H2O2 rendering it harmless. Thus, if selenium is low then this antioxidant enzyme is not made at optimal levels and the thyroid is damaged in proportion to the level of selenium deficiency. The thyrocytes also make another selenium dependent enzyme called thioredoxin, which also acts as an antioxidant to clear H2O2.

Selenium is Needed for Thyroid Hormone Regulation

Your thyroid gland’s production of thyroid hormone is certainly important. However, it is only part of a much broader and very complex regulatory scheme that your body uses to determine how to use thyroid hormone so that you have a good energy level and proper metabolic rate. The thyroid hormone your thyroid gland produces, T4, is not biologically active. T4 is activated and deactivated by three enzymes called iodothyronine de-iodinases, types I, II, and III (known as IDI, IDII, and IDIII). All of these enzymes require selenium to function.

IDI converts T4 to T3. T3 is the active thyroid hormone that will be used by your cells to set metabolic rate. This takes place mostly in your liver, and also in your kidneys and muscles – the other places that tend to have higher selenium content when selenium levels are adequate. Once the T3 is produced in these key areas it is transported around your body so that cells can use it.

Your brain has its own system of thyroid hormone activation, which utilizes IDII to convert T4 to T3 on a cell by cell basis. This system is necessary so that your brain can keep working even if you are in a starvation situation and the rest of your body has had to slow down.

The activities of IDI and IDII enable your metabolism to go. The brakes for this system are managed by IDIII, which converts T4 to inactive reverse T3 or it converts T3 to inactive T2. Just as you can’t drive a car without brakes, you can’t run metabolism properly without an efficient way to slow it down. This natural process is governed by IDIII.

The main point of all this is rather plain: a lack of selenium leaves your body in a thyroid funk.

Selenium Deficiency

The preservation of thyroid hormone function is of the utmost importance to survival, as thyroid sets the pace for all cellular activity. When selenium runs low, your body has tough choices. The selenium reserves in your thyroid gland and your brain are the last to diminish. For example, under selenium deficiency the activity of thyroid related function can decrease by 99 percent in your liver, kidneys, and muscles while only dropping by 50 percent in your thyroid gland and brain.

Such a scenario would typically be a response to starvation and reminds us of the vital need to keep your brain functioning (so you can hunt and gather food should you see any). In modern times, processed food and mass produced food grown without care of the soil (no selenium left in the soil) has led to wide ranging selenium deficiency.

In addition to direct problems for the thyroid gland the lack of selenium impairs metabolic rate, setting off a chain reaction with any other type of health problem as a possible consequence. In other words, when cells can’t make energy properly because metabolic rate is impaired, then whatever those cells were supposed to be doing doesn’t get done at any optimal rate. If you have a genetic weakness, under the condition of poor thyroid function, it is more likely to manifest.

Selenium is also used by your body for immunity and detoxification activities. In conditions of selenium deficiency we have a number of vital body systems crying out for selenium. You can induce a selenium deficiency by working around chemicals, eating foods with too many chemicals on them, or by breathing air with too much pollution in it. A poor health trend in and of itself tends to use up selenium – thus many people with chronic health issues lack selenium. Any of these issues then results in compromised thyroid function on top of other health issues, with the tendency to worsen each other as time goes along. This scenario is all too common in America today and underlies a great deal of the health misery that so many people experience.

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