Also known as: Potassium iodide, Kelp iodine, Iodide, Lugol's, I
MineralsStrong evidence
A trace mineral needed for thyroid hormone production and almost nothing else. Both too little and too much cause problems, which makes it one of the few nutrients where overshooting is as bad as falling short.
Typical dose
150.0–150.0 mcg per day
Any time, with or without food
What it is
Iodine is a trace mineral with essentially one job: it is a structural component of thyroid hormones, which regulate metabolic rate throughout the body.
In the UK, dairy is the main source, largely because of iodine used in cattle feed and udder disinfection rather than anything about milk itself. White fish and seafood are also rich. Unlike many countries, the UK does not routinely iodise table salt, which means British intake is more dependent on dairy than most people realise.
That matters for anyone moving away from dairy. Most plant milks are not fortified with iodine, and swapping cow's milk for an unfortified alternative removes a major source without any obvious replacement. This is one of the more genuine and less discussed nutritional consequences of that switch.
How it works
The thyroid gland actively concentrates iodide from the bloodstream and attaches it to a protein scaffold to build thyroid hormones. The two main hormones are named for how many iodine atoms they carry.
Those hormones then set metabolic rate across virtually every tissue, influencing energy expenditure, body temperature, heart rate and growth.
Converting the storage form into the active form requires selenium, which is why the two minerals are so closely linked. Adequate iodine with poor selenium status leaves the system only partly functional.
What the evidence shows
Iodine's role in thyroid hormone production is beyond dispute and among the most firmly established facts in nutrition. Adequate intake during pregnancy is particularly important for the developing child.
Surveys have repeatedly found that a meaningful proportion of UK women of childbearing age have intakes below recommended levels, which makes this a more relevant nutrient here than it might appear.
There is no evidence of benefit from supplementing beyond requirement, and good reason not to. Excess iodine disrupts thyroid function just as shortfall does, and the high-dose kelp and Lugol's products sold for energy or metabolism are a genuinely poor idea rather than merely a waste of money.
Dosing
Reference intake is 150 micrograms daily for adults, rising during pregnancy and breastfeeding.
A supplement supplying around 150 micrograms is appropriate for anyone whose diet is low in dairy and fish. That is the dose to look for, and there is no reason to seek out more.
Avoid high-dose kelp products. Seaweed iodine content varies enormously and unpredictably, and some kelp supplements supply many times the daily requirement in a single serving. If you use seaweed as a source, choose a product that declares its iodine content, and treat anything that does not as unquantifiable. The tolerable upper intake is 600 micrograms daily.
At a glance
Common forms
Potassium iodide, Potassium iodate, Kelp extract, Lugol's solution, Within multivitamins
Half-life / duration
Thyroid stores buffer intake over weeks
Timing
Any time, with or without food
Competition status
Permitted — not on the WADA Prohibited List
Category
Minerals
Safety and side effects
At intakes near requirement, iodine is safe and unremarkable. The unusual feature of iodine is that too much disrupts thyroid function in much the same way as too little, and both directions are documented.
This is why high-dose products deserve scepticism. Kelp supplements in particular can supply wildly variable amounts, and there are documented cases of thyroid disruption traced to them.
Anyone whose thyroid function is being monitored or medicated should not take iodine supplements without medical advice. Count any seaweed products, including sea moss, toward your total.
Who should avoid it
Do not take iodine supplements if your thyroid function is being monitored or medicated without medical advice. Do not exceed 600 micrograms daily from all sources. Count seaweed and sea moss products toward your total. Avoid high-dose kelp products with undeclared iodine content. Speak to your doctor before use in pregnancy, where requirements change.
This entry is provided for information only. Food supplements should not be used as a substitute for a varied and balanced diet and a healthy lifestyle. Consult a qualified healthcare professional before use if you are pregnant, breastfeeding, taking medication or under medical supervision.
