Where do you get iodine without dairy or fish? Tap your foods and see

Where does iodine come from if you skip dairy and fish?

Iodine is a mineral your thyroid uses to make hormones that help set your energy use, growth and, in pregnancy, a baby's brain development. Your body cannot make it, so it has to come from food. Adults need about 150 µg a day (the EFSA reference; the NHS says 140 µg). A microgram, written µg, is a millionth of a gram.

The catch for people eating plant-based is that the usual sources are milk, yoghurt, eggs and sea fish. Plants hold only a little, and how much depends on the soil they grew in. A UK study that tested 44 unfortified plant drinks found a median of about 0.7 µg per 100 ml, against roughly 44 µg per 100 ml in ordinary cow's milk.

Tap the foods you eat in a typical day below and see where you land. Use the average of a normal week in your head: health bodies look at intake over weeks, so one low day is not a problem.

What the numbers show

Most of the weight sits in a few foods. A glass of milk, a pot of yoghurt or a portion of white fish each does a large share of the work. On a fully plant-based day, the realistic routes are fortified plant drinks, iodised salt and, for some people, a supplement. The Vegan Society lists about 500 ml a day of a fortified drink with around 25 µg per 100 ml as a reliable option.

Iodised salt is not a reason to eat more salt. The WHO advises keeping salt under 5 g a day, and in some countries most table salt is iodised while in others very little is. Sea, kosher and Himalayan salts usually are not. Check the label for "iodised" or "potassium iodide".

Plant-based does not mean low iodine by default. It means iodine needs a plan, because the soil-dependent plant sources are hard to count on.

What about seaweed and supplements?

Seaweed is the tricky one. Brown types such as kombu, kelp, wakame and arame can hold thousands of µg per gram dry weight. The German BfR notes that even 1 to 10 g of some of these can push an adult far past the upper level, and the British Dietetic Association says to keep them to once a week at most, and to avoid them in pregnancy. The amount varies so much from batch to batch that it is not a dependable source. That is why the tool above leaves it out.

For the same reason, the BDA advises against kelp or seaweed supplements. Where a supplement makes sense it is usually a small one with potassium iodide or potassium iodate. Sources differ on whether vegans should routinely take one: the Vegan Society and BDA say to consider it, while the NHS suggests fortified foods or a supplement, and there are no official UK recommendations for dose. Too much can affect the thyroid as well as too little.

Who should check with a professional first

This guide is general information, not medical advice. Talk to a doctor, midwife or dietitian before changing how you get iodine if you:

• are pregnant, breastfeeding or planning a pregnancy, when needs rise (EFSA uses 200 µg a day);
• have a thyroid condition or take thyroid medication, since both extra iodine and too little can matter;
• have or have had an eating disorder, or take other regular medication;
• are feeding a child a fully plant-based diet.

A simple way to cover it

1. Pick a plant drink that lists iodine on the label and have a couple of glasses over the day, or
2. Use iodised salt in cooking in your usual small amount, not extra, or
3. If neither fits you, ask a dietitian or pharmacist whether a small supplement is right for you.

Sources

• NHS: Iodine
• British Dietetic Association: Iodine food fact sheet
• German Federal Institute for Risk Assessment (BfR): iodine intake, salt and seaweed
• US NIH Office of Dietary Supplements: Iodine fact sheet
• The Vegan Society: Why is iodine important?
• Report on Bath et al., British Journal of Nutrition 2017: iodine in milk alternative drinks