Iodine

It is important not to over-consume iodine as it has a relatively narrow range of intakes that reliably support good thyroid function.

The element iodine is a key component to our overall health.  Found in certain seaweeds in high amounts, iodine is not found in great levels away from the seashore.  The only well known function for iodine in the body is as a component of the thyroid hormones T3 and T4.  Most of the iodine in our diet comes from iodized salt (fortified) or various seafoods.

Source

The best source of iodine is sea vegetables (seaweed).  Sea vegetables have lots of B-vitamins and lots of minerals, particularly the trace minerals such as iodine.  The only problem with seaweed is that you can actually get too much iodine.  The World Health Organization places the safe upper limit of iodine intake at 1000mcg per day for adults, and less for children – even 300mcg may be too much for a five year old.

Nori is low in iodine and several sheets a day can be eaten without any concern about excess iodine.  Frequent addition of small amounts of powdered or crumbled seaweed to stews or curries while cooking, or to other foods as a condiment, is an excellent way to provide adequate iodine in the absence of other supplementation.  100gm of dried hijiki or 15gm of dried kombu or kelp in a convenient container in the kitchen provides one year's supply for one person.  More is not better.

Supplemental iodine can come in salt forms, such as potassium iodide; or by supplying food sources such as kelp.

Instructions

The current US RDA for iodine is 150mcg.  About 100-300mcg per day is desirable, although intakes of up to 500mcg per day are probably not harmful.  If taking supplements for iodine go for about 100-150mcg per day, to give a total intake of 150-200mcg per day.

Some otherwise healthful foods contain goitrogens – substances that can interfere with iodine uptake or hormone release from the thyroid gland.  These foods are generally only a concern if iodine intake is low.  Consumption of brassicas, such as cabbage, Brussels sprouts, broccoli and cauliflower, increase the requirements for iodine, especially if consumed raw.

Side-Effects

Someone consuming large amounts of iodised salt or seaweeds could readily overdo it.  If using seaweeds as an iodine source it is best to use seaweeds that have been found to have fairly consistent iodine content, such as kelp (kombu) or hijiki.  Consumption of more than 100gm per year (dried weight) of most seaweeds carries a significant risk of thyroid disorder due to iodine intakes in excess of 1000mcg per day.