Wisdom Wednesday: Thyroid and the Immune System

I have written frequently about the role of the thyroid in general metabolism, production of the hormones T3 and T4, and the thyroid autoimmune disease Hashimoto’s thyroiditis. The thyroid gland also serves an important role in your immune system.

There is increased interest in the role of autoimmune disease on the health of the thyroid. Some experts state that fully a third of all cases of hypothyroidism are due to the autoimmune disease Hashimoto’s thyroiditis. However, there is little or no interest the reverse scenario – the thyroid’s effect on the immune system.

We know that thyroid hormones have the ability to dampen the cytokine load. Cytokines are chemicals released from the immune system. When we are unable to control the cytokine load systemic inflammation ensues. Increased cytokines also can suppress TSH (thyroid stimulating hormone), can decrease conversion of inactive T4 to active T3, and make thyroid hormonal binding sites in the cells less responsive. So hypothyroidism and inflammation become a vicious cycle.

Iodine also plays an essential role in immune function. Dietary iodine is collected in the thyroid gland where it is used to form thyroid hormone. T3 is three molecules of iodine attached to cholesterol. T4 is four molecules of iodine attached to cholesterol. When iodine stores in the thyroid are adequate, iodine also acts as a disinfectant.

My analogy is a salt water pool. Rather than load the pool up with chlorine to keep the algae at bay, salt (NaCl) is added to the fresh water. When water flows through the pump a small cylinder sends an electric charge through less than one gallon of the water, changing the salt to chlorine. The water in the cylinder is super chlorinated, killing the algae, but the amount of chloride that ends up in the pool is minimal. Of course this system only works when the pump is running and requires adequate salt in the pool.

In much the same way, blood is constantly coursing through the thyroid. When iodine status is adequate, the iodine disinfects the blood much like the chlorine does in the pool. Obviously, the pump (heart) works 24/7, but iodine status is typically low in much of the population.



Iodine appears to be an important factor in the prevention of reproductive cancers – prostate, uterus, ovarian and breast. In Northern Japan, where seaweed is a stable of the diet, the average daily intake of iodine is 12.5mg. The RDA (recommended daily allowance) is 180mcg, just a small fraction of that amount. Reproductive cancers are almost nonexistent in Northern Japan but do increase slightly as you move from the seashore up into the mountains. However, even in the higher elevations the rate of these cancers is less than 20% of the rate in the U.S.

Iodine and chloride, along with fluoride and bromine are all in the chemical family called halides. They occupy the 7th column in the periodic table (remember your high school chemistry?). All these elements are missing one electron from their outer shell. As a result, they all crave that one electron and react is similar fashion chemically.

Iodine is essential for human health, but the other halides can replace iodine in the body with repeated exposure. Often supplementing iodine will force the other halides out of the tissues creating a toxic effect as the body works to eliminate these toxins. Competitive swimmers and people with high fluoride content in their drinking water are commonly affected.

Supplementation of iodine above the RDA should be monitored by a health care professional well versed in iodine metabolism. Your iodine status and halide toxicity levels can be measured with a 24-hour urine analysis.

The Bottom Line:
You’re probably well aware of the potential issues surrounding an autoimmune attack on your thyroid. However, you should also be aware how important thyroid function is to a well-functioning immune system.