Iodine

Iodine is an essential mineral in the diet due to its importance towards cognition and fetal development secondary to being required for thyroid hormones; iodine is central to the active thyroid hormones T3 and T4, and a true iodine deficiency results in less of these hormones and may result in reduced cognition (if a subclinical deficiency) or cretinism (severe deficiency in utero).

Despite the importance of iodine, it is not a common dietary supplement. This is due to table salt being iodized (added iodine) and even relative deficiencies being quite rare in first world countries (it is a common issue in developing countries due to iodine only naturally occurring from fish and seaweed which may not be consumed); actually benefitting from supplementation of iodine requires a 'perfect storm' of situations to occur which are outlined in the dosing section but not many people will meet these requirements.

Supplementation of high doses of iodine in otherwise healthy people does not appear to result in much, since it is readily excreted and normalized. There may be a very small and (clinically) irrelevant antiinflammatory effect and a small reduction in thyroid hormones (rather than an increase), but that seems to be it. Obscenely high doses for a prolonged period of time, which occurs with consumption of unprocessed seaweed (mostly kombu) will result in benign goiter in all persons and thyrotoxicity in some persons with underlying thyroid issues.

Supplementation of iodine is designed to circumvent a deficiency, and deficiencies of iodine are quite rare in first world countries. For those in a first world country, iodine should only be considered if you meet all of the following requirements:

• You are a vegetarian or vegan who actively avoids processed foods, or a meat eater who never eats fish and avoids processed foods

• You avoid adding additional salt to your diet

• You avoid consumption of seaweed or seaweed based products (such as sushi, which are wrapped with Nori)

Assuming all the criteria are met, recommendations for iodine intake tend to be in the range of 75-150 μg (micrograms) or 0.075-0.15 mg daily while higher doses are not inherently dangerous although there may be a slight suppression of thyroid hormones (T3 and T4) at 500 μg or above.

The Human Effect Matrix looks at human studies (it excludes animal and in vitro studies) to tell you what effects iodine has on your body, and how strong these effects are.

Grade	Level of Evidence [show legend]
	Robust research conducted with repeated double-blind clinical trials
	Multiple studies where at least two are double-blind and placebo controlled
	Single double-blind study or multiple cohort studies
	Uncontrolled or observational studies only

Level of Evidence ? The amount of high quality evidence. The more evidence, the more we can trust the results.	Outcome	Magnitude of effect ? The direction and size of the supplement's impact on each outcome. Some supplements can have an increasing effect, others have a decreasing effect, and others have no effect.	Consistency of research results ? Scientific research does not always agree. HIGH or VERY HIGH means that most of the scientific research agrees.	Notes
	Serum T3	Minor	High See all 3 studies	500µg iodine or higher (in addition to the diet) appears to have a slight suppressive effect on thyroid function in otherwise healthy persons
	Serum T4	Minor	Moderate See all 5 studies	Supplemental iodine above 500µg appears to be capable of suppressing T4 to a small degree whereas lower doses are not associated with such an effect.
	Thyroid-Stimulating Hormone	Minor	High See all 3 studies	An increase in Thyroid Stimulating Hormone (TSH) occurs both at the doses that suppress T3 and T4 and sometimes at lower doses where thyroid function is not impaired
	Thyrotropin Releasing Hormone	Minor	- See study	Alongside the suppression of circulating thyroid hormones and TSH, there is a mild and transient increase in levels of the hormone that stimulates TSH known as thyrotropin releasing hormone (TRH)
	C-Reactive Protein	Minor	- See study	There may be a small decrease in C-reactive protein associated with moderate iodine supplementation in otherwise healthy persons, indicative of an antiinflammatory effect.
	Interleukin 6	Minor	- See study	There is a minor decrease in circulating IL-6 associated with iodine supplementation, thought to be indicative of a minor antiinflammatory effect.