Sources of iodine in food is up 60 percent in search this week, level with natural sources of iodine, also up 60 percent, and just ahead of foods with iodine in them, up 50 percent. The steady searches underneath are simpler still: what is iodine holds a volume score of 100, iodine salt sits at 47, iodine foods at 25, iodine element and iodine food at 19 each, iodine in salt at 17, and what has iodine at 16.

Put those side by side and you get a food question and a chemistry question asked at the same time. People want to know what iodine is and where it turns up at dinner, and a good number of them go straight to the salt shaker.

Plenty of the other searching around iodine is about how much a person needs, and about pregnancy. Those are questions for a qualified healthcare professional rather than for a company selling a bundle, and this article does not answer them. It covers the element, the food, and the odd route iodine took from seaweed ash to the table.

What is iodine, as an element

Iodine is element 53. The Royal Society of Chemistry's periodic table places it in group 17, the halogens. In its pure form it is a black, shiny, crystalline solid, and when it is heated it sublimes, passing straight from solid into a purple vapor.

That vapor gave the element its name. According to the Royal Society of Chemistry, iodine comes from the Greek word iodes, meaning violet.

It was also first found in seaweed. The society's history of the element records that in 1811 a chemist was processing seaweed ash to make saltpeter, added sulfuric acid, and watched purple fumes rise and form crystals. Those crystals turned out to be a new element.

The same source lists a long spread of modern uses: pharmaceuticals and disinfectants, printing inks and dyes, catalysts, animal feed supplements, photographic chemicals, and the polarizing filters in LCD screens. That is why an iodine search can land on a chemistry homework page, a first-aid shelf or a food label, depending on the word typed next to it.

Sources of iodine in food start in the sea

It fits that iodine was first isolated from seaweed. The USDA, FDA and NIH Office of Dietary Supplements Database for the Iodine Content of Common Foods, first released in June 2020, explains that iodine is present naturally at relatively high levels in seaweed, many saltwater fishes and other seafood, because those organisms concentrate it from the seawater around them.

The same database names the notable food sources of iodine that researchers have analyzed: seaweed, fish and other seafood, dairy foods, iodized salt, and eggs. So the short answer to what has iodine, as a matter of food composition, is a list that starts in the ocean and ends in the fridge.

What the database is careful not to do is pretend that any of those foods carries one fixed amount. Its authors describe a wide range of iodine concentrations within individual foods, and that variation is where the more interesting part of the story sits.

Natural sources of iodine, and why "natural" is hard to pin down

Natural sources of iodine is one of this week's fastest risers, and it is a harder phrase than it looks. The database lists the reasons iodine levels in food vary, and they are a mix of geology and human practice:

• Soil. Crops reflect the amount of iodine in the soil they were grown in.
• Animal husbandry. The extent to which farm animals are given iodine is one of the named factors.
• Sanitizers. Iodine-based sanitizing agents, called iodophors, are another.
• Processed-food ingredients. Some breads use iodate as a dough conditioner, and the database gives those breads separate entries because their values differ so much from breads made without it.

It even set aside several foods whose high iodine readings were likely down to erythrosine, a cherry-colored dye also known as FD&C Red No. 3, used in things like glace cherries, some candies and decorating gels.

So is the iodine in a glass of milk natural? The element is. How much of it ends up there depends partly on farm practice and processing. Seaweed and saltwater fish are the cleanest examples of foods that carry iodine because of where they live. Much of the rest is a blend of environment and handling, which is why natural is a fuzzy filter here and why the better question is simply which foods, and why.

Iodine in salt is an addition, not a property

Iodine salt is the second-biggest steady search in this cluster, and it describes something done to salt rather than something salt is. According to a 2022 paper in the Journal of Food Composition and Analysis describing the NIH, FDA and USDA iodine database, salt iodization in the United States was adopted on a voluntary basis in 1924.

Voluntary is the word to hold onto. The same paper notes that most of the salt consumed in the US is not iodized, and that salt used commercially typically is not iodized either. The database itself gives iodized table salt, iodized sea salt and non-iodized sea salt their own entries, and the non-iodized sea salt samples came in below the level its method could measure.

So iodine in salt is a label question, answered by one word: iodized. The type of salt does not settle it, since sea salt appears on both sides of that line. We compared the salts themselves as materials in pink salt, sea salt and table salt, and that piece stays on the rocks. This one is only about the added element.

One more reading habit, because iodine does not always show up on an ingredient list under its own name. The database notes that the breads it analyzed had labels listing potassium iodate or calcium iodate as a dough conditioner. Those are compounds, not the element. In chemical naming, an -ide ending such as iodide names iodine as a simple ion, and an -ate ending such as iodate names iodine bound up with oxygen. If you are looking for where iodine sits on a label, those two endings are the words to scan for, and the word iodine on its own may never appear at all.

Iodine is not the only element a bundle listing like this one names. Selenium lives an even stranger double life, as the element everyone associates with Brazil nuts and with dandruff shampoo, and it has a naming story of its own.

Our take

We think iodine has one of the best origin stories of any element named on a supplement listing, and almost nobody hears it.

It was found by someone making saltpeter out of seaweed ash. It was named for the color of its vapor. More than a century later, iodized salt arrived in the United States on a voluntary basis. That is chemistry, industry and food policy in one element, and this week's search data shows people circling all three at once: the element, the food and the shaker.

Our view is that food literacy starts with pulling those threads apart. Where an element occurs, how it got into a product, and whether a particular person needs more or less of it are three different questions. The first two are facts you can read from a database or a label. The third belongs to a clinician, and for anyone who is pregnant or breastfeeding it belongs there without exception.

Why we carry it at PRSPR

Our Pre & Post Natal Bundle is a set of individual products sold together, each with its own supplement facts panel. Its listing names iodine among the minerals it attributes to the bundle's seaweed component, which is why iodine is the element this article is about. That is how the listing puts it, and we are not attaching a figure or anything else to it.

What we will add in our own voice is the quality story alone. Each product in it is made in a GMP-certified facility and third-party batch tested, so what is on the label is what is in the bottle. No guessing, no filler.

If the word on the box is the thing you are trying to decode, why prenatal is a category, not an ingredient is the place to start. Otherwise open the bundle page and read each panel, browse the bundles collection, or take the build-your-stack quiz.