Assigned the symbol I and the atomic number 53 in the periodic table, iodine is a trace-element. Relatively rare in the natural environment, it’s found at low levels in seafood (1). It was actually first discovered in seaweed ash in 1811. Its name comes from the Greek iodes meaning ‘violet-colored’, reflecting the purple color of its vapour when heated.
Iodine plays a direct role in ensuring good thyroid function and normal production of two thyroid hormones: T3 (triiodothyronine) and T4 (thyroxin), which contain 3 and 4 iodine atoms respectively (2). It also supports normal energy metabolism and helps maintain healthy skin, as well as normal nervous system and cognitive function (3-5).
As a reminder, the thyroid is a small, butterfly-shaped gland located at the base of the throat which plays an essential role in maintaining vital functions in the body. Amongst others, it governs the heart rate, body temperature, growth, skin appearance, appetite, weight and mood (6).
Since our bodies are unable to produce iodine, we have to obtain it from the diet to ensure our needs are met.
Official sources estimate adequate intakes to be 90 mcg/day for children, 130 mcg/day for adolescents, 150 mcg/for adults and 200 mcg/day for women who are pregnant or breastfeeding (7).
A lack of iodine impairs thyroid function. Chronic iodine deficiency can thus lead to the development of a goitre - an enlargement of the thyroid gland and/or the appearance of nodules (8).
In the case of proven deficiency, which is admittedly very rare, there’s a significant slowing down of thyroid function. This is called hypothyroidism (9) and it produces various symptoms, including weight gain, intense fatigue, constipation, pallid skin and attention problems (10).
However, despite it being essential for health, iodine should never be ingested at excessive levels as this can lead to malfunction of the thyroid gland (11). The European Union has thus set an upper safe limit of 600mcg/day, though it must be said the risk of ‘over-dosing’ is extremely low, especially since any surplus iodine is theoretically excreted via urine (12).
In the 1950s, public authorities called for iodine to be added to salt in order to eradicate deficiency. This led to the creation of iodised table salt which became the primary source of dietary iodine across the world. However, we now know that a high-sodium diet increases the risk of cardiovascular problems and the WHO recommends we eat less than5g of salt a day, around half the average amount actually consumed (13).
In addition to iodised salt, iodine is found in seaweed (kombu, dulse, wakame), seafood, egg yolk and dairy products (14).
In most cases, a sufficiently-varied diet with plenty of seafood and dairy products should be enough to cover our iodine needs. However, certain groups may be at higher risk of deficiency than others:
If you wish to take an iodine supplement, we’d suggest first consulting a health professional. They can carry out a blood or urine test to confirm your iodine status and thus evaluate whether supplementation is appropriate.
For those looking to reduce their salt intake, the best option is to supplement with Ascophyllum nodosum (try the product Natural Iodine) (19). Gathered off the coastlines of Western Scotland and Ireland, this seaweed has a sodium content 10 times lower than that of salt for the same amount of iodine.
Tablets based on potassium iodide - the product of a reaction between potassium hydroxide and iodine - offer unbeatable stability and exceptional bioavailability, assessed at 96.4% (20). Potassium iodide is the form used for cooking salt, as well as for the iodine pills given to populations following nuclear accidents (to saturate the thyroid and prevent uptake of radioactive iodine, which causes serious damage to the thyroid) (21). However, be sure to choose a safe formulation with a moderate dose (such as Potassium Iodide, which contains 200mcg of iodine per tablet).
Certain cutting-edge formulations combine iodine with various thyroid-beneficial compounds (the synergistic supplement Natural Thyro Formula combines iodine from kelp with selenium, which supports normal thyroid function, and extract of guggul, which also helps to maintain thyroid health) (22-23).
Last but not least, multivitamin supplements, which incorporate smaller amounts of iodine, are more suitable for daily use (revised in 2019, the exceptional formulation Daily 3 contains no less than 42 carefully-selected, natural-source ingredients including 50mcg of iodine per capsule).
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