The WHO has estimated that approximately 2 billion people are at risk of becoming iodine deficient throughout the world. This is about one-third of the world's entire population. Iodine deficiency is the leading cause of hypothyroidism in the world.
In the United States, the Food and Drug Administration conducts yearly total diet studies on amounts of nutrients that are in our food supply as part of the United States National Nutrition Monitoring System. These studies help monitor the safety of the food supply and determine if there are changes in vitamin or mineral status that may affect public health. More than 260 foods are analyzed for dietary iodine.
Demographic data from the National Health and Nutrition Examination Survey (NHANES) includes information on iodine status in the United States. According to the data compiled from 1988 to 1994, iodine status overall in the United States is sufficient. However, the consumption of iodine is falling, and more people in all age groups are considered iodine deficient.
It is alarming to many doctors and scientists that 14.9 percent of women in their reproductive years are iodine deficient in the United States. This is particularly disturbing, as iodine is known to be essential to the developing fetus and in early infancy for brain and neurological function. The WHO recommends 150 mcg per day of iodine for adults, and if pregnant or lactating, 200 mcg per day.
Correction of iodine deficiency is normally based on adequate levels of dietary iodine. It is dangerous to take extremely high amounts of supplementary iodine. The advice from many health care professionals is to include foods that contain iodine in the diet such as iodized salt, milk, and seafood.
Reasons for the decreasing dietary iodine in the United States are decreased use of iodized salt, reduced amounts of iodine in milk, and the reduced intake of cow's milk. Changing from iodized salt to sea salt decreases the amount of dietary iodine in the diet. Sea salt is low in iodine, with approximately 64 mcg of iodine in 2.2 pounds (1 kilogram). This compares to 400 mcgs in 1 teaspoon of iodized salt.
To evaluate iodine status in populations, urine levels of iodine are measured. The human body eliminates approximately 90 percent of ingested iodine. If very little iodine is excreted, it is an indicator of iodine deficiency. Evaluating levels of TSH, T4, and T3 is also used to diagnose low iodine status. If a goiter develops due to lack of iodine, a biopsy usually needs to be taken in order to make sure cancer is not present.
In the late 1970s, results of studies conducted by the United States, titled “Food and Drug Administration, Total Diet Studies,” showed a very high iodine level in many dairy products. The results were shared with the dairy industry, and the iodine-containing cleaning supplies (iodophors) were reduced.
The synthesis of thyroid hormone is dependent on adequate supplies of iodine. Endemic goiters (goiter that develops from lack of iodine) may develop when iodine is missing from dietary sources or medication. For some people with thyroid disease, getting too little or too much iodine can lead to hypothyroidism.
In normal thyroids, if there is excessive iodine, the body will block iodine from being incorporated into thyroid hormone. This prevents hyperthyroidism from developing. In some people, especially those with autoimmune thyroid diseases such as Hashimoto's or Graves' diseases, this mechanism does not work properly. If large amounts of iodine are consumed for a long period of time, hypothyroidism may develop.
Make sure you get enough iodine, but don't think that if a little is good a lot is better and excess is even better than that! In most instances, it's not a problem to enjoy foods that contain iodine. Ask your medical team for advice if you wish to start eating foods on a regular basis that contain large amounts of iodine like sea vegetables. Don't take excessive supplemental iodine (kelp tablets, large doses of iodine, etc.) without your physician's guidance.