Nutrition And Thyroid Function

As noted in an earlier post, we are seeing an absolute epidemic of autoimmune thyroid disease.  Many patients have low levels of antibodies but I have seen some patients with antibody levels so high they are not measurable by my lab.

In general patients with low levels of anti-thyroid antibodies may have no symptoms at all.  However many patients are tired, constipated, depressed and gaining weight in spite of a healthy diet and regular exercise.

What is the link between nutrition and thyroid disease?

The addition of iodine to table salt was one of the first attempts to prevent a disease through a public health measure.  Its success led to other such measures, such as the addition of fluoride to city drinking water and folic acid to bread and other grain products.

Iodine is an essential mineral for thyroid function.  However, it is a double-edged sword.  Soon after the problems of iodine deficiency subsided, it was noticed that more and more cases of autoimmune thyroiditis were being seen.  Autoimmune thyroiditis is now the most common cause of thyroid disease.

It seems that iodine is a nutrient that has a narrow window of safe intake.  Too little and the thyroid can’t function well because it can’t make thyroid hormones.  Too much and it is associated with an autoimmune reaction that attacks the thyroid tissues.

(To be clear, it is not understood how autoimmune thyroid disease comes about.  A clear cause has not been identified and it’s entirely possible that excess thyroid intake is ASSOCIATED with autoimmune thyroiditis but not a CAUSE.  An association does not prove a causative relationship.)

How much is enough, and how much is too much?  As of right now, the recommended daily intake (RDI) of iodine is 150 mcg, 220 mcg in pregnant and breastfeeding women.  It seems that more than 300 mcg of daily intake is associated with increased risks of autoimmune thyroid disease.

So for iodine, it seems like less than 150 mcg per day is too little, and more than 300 mcg per day is too much.

What about selenium?  Selenium is a trace mineral that is very important for thyroid function.  Changing thyroxine (T4) to the active form of thyroid hormone (T3) requires an enzyme that depends on selenium to function.

Low blood selenium levels are more common in patients with Hashimoto’s disease and Grave’s disease, two of the most common autoimmune thyroid diseases.  Selenium supplementation reduces inflammatory molecules and also decreases blood levels of antibodies against the thyroid gland.

Can you get too much selenium?  The RDI is 70 mcg but when I have a patient with Hashimoto’s disease I ask them to take 200 mcg in addition to their multivitamin.

Iodine is present in particularly rich amounts in foods that come from the sea.  Fish, shellfish and seaweed are excellent sources.  Check here for more information about foods that are good sources of iodine.

Blood tests are not reliable for iodine intake, although they are accurate for selenium.  The best test to check your iodine status would be a 24-hour urine excretion.  You can ask your doctor to order these tests if you have Hashimoto’s or Grave’s disease or hypothyroidism.

It is good to take a multivitamin that has 100% RDI of iodine, especially if you avoid using the salt shaker or if you prefer to use sea salt or Himalayan salt.  Neither of those salt products have iodine in them.

If you have autoimmune thyroid disease (or want to avoid getting it) make sure you are getting the right amount of iodine in your diet.  You should also consider taking extra selenium.  Asking your doctor to check levels of these two nutrients may be helpful, but isn’t absolutely necessary.

Source: Duntas LH. Horm Metab Res. 2015 Sep;47(10):721-6

QUESTION: Do you have Hashimoto’s disease or Grave’s disease?  Do you watch your iodine and selenium intake?


2 thoughts on “Nutrition And Thyroid Function

  1. Hi Dr. Jennifer: You are the one who said my thyroid was and low and I have been on 75mgs of snythroid ever since. I just had blood work and Dr. Matt said levels were fine. Should I be tested for Selenium level?
    Rene Kupcik

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