SeaweedIodine is essential in the making of thyroid hormone. Low thyroid has particularly severe consequences if present while pregnant (see below).  In the thyroid gland under stimulation from Thyroid Stimulating Hormone (TSH) that comes from the hypothalamus, iodine is added to thyroid hormone to make triiodothyronine (T3) and thyroxin (T4).

While it is T4 that is most abundant in the blood, the active thyroid hormone is Free-T3, formed in the tissues by enzymes that convert T4 to T3.  In the body, thyroid hormones are important for:
    – Normal brain development in the womb and during childhood (needed for myelination).
    – Normal growth and development.
    – Reducing thyroid disease, goiter, breast cancer, and fibrocystic disease, as well as prostate cancer. 
    – Thyroid hormone acts on all cells in the body, which is important for metabolism, including the heart.



Iodine deficiency is the leading cause of preventable brain damage in the world, and thought by the world health organization to affect 740 million people.  The most concerning is the brain damage to unborn children that are born to moms who are low in iodine.  Since Iodine is needed for myelination of the central nervous system, the most severe forms are called cretinism, and typically present with irreversible mental retardation, deafness, and physical growth retardation with short stature and myxedema (swelling). 

Mild forms may often be detected by the presence of a goiter (enlarged thyroid gland). School-aged children may have poor school performance, slower response times, ADHD, and other learning issues. 

Iodine is protective against radiation damage, and thyroid cancer that can result from excessive radiation exposure.  This has been vital in accidents like the 1986 Chernobyl nuclear accident, the more recent Fukushima reactor accident in Japan ,and also in cases where radiation for medical treatment is excessive and near the thyroid gland in the neck.  Iodine may benefit fibrocystic breast disorders, suggestive that deficiency may be a contributing cause. 



Almost all the iodine that is available is in the sea, and seaweed is by far the best food source of iodine other than iodine supplemented foods (iodine salt, iodized vegetable oil). 
Seaweed (1 ounce)                             up to 18,000 (18 grams)
Cod (3 oz)                                           99
Iodized salt (1gm=1/3tsp)                   77
Potatoes with skin (1)                          63
Milk (8oz)                                             56
Seafood                                               17-35
Navy beans (1/2 cup cooked)              35
Egg (1)                                                 29



Acute poisoning is very rare, may present with burning of the mouth, throat and stomach, nausea, vomiting and diarrhea, fever, stomach aches, and,  rarely, a weak pulse and coma have been reported. 

In Japan, where lots of seaweed is eaten, dietary intakes as high as 50,000 or more (50mg) a day have not resulted in any toxicity.  Since elevated TSH has been seen with iodine intakes over 1700 micrograms (1.7grams) a day the following upper limits were set:


                             micrograms / day
Infants                      unknown
Children 1-3                 200 
Children 4-8                 300
Children 9-13               600
Teens/adults               1000

If your diet contains some seaweed, that is great.  If not, you would be wise to supplement a little iodine.  Pregnancy recommendation is to take 150 micrograms a day.  Not all prenatal vitamins contain iodine.  If not, please be sure you get your 150 micrograms either from the diet or as a supplement. 


Here are some links that you may find helpful:

Iodine: Health Implications of Deficiency…

Iodine intake as a determinant of thyroid disorders in populations…

Screening for thyroid disease and iodine deficiency…

Overt and subclinical hypothyroidism: who to treat and how… 

Thyroxine (T4) and tri-iodothyronine (T3) determinations: techniques and value in the assessment of thyroid function…

Thyroid hormone and the cardiovascular system…


Dr. Paul







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