Korean Laver (Gim) Iodine: 100 mg/kg vs 2,432 for Kelp

A Korean article dated August 4, 2025 says a single sheet of seasoned gim (김, roasted laver, about 2 g) carries 200 to 300 µg of iodine, and that "조미김 단 한 장만 먹어도 하루 권장량을 가뿐히 넘어서게 됩니다", which is "even one sheet of seasoned gim easily passes the daily recommendation." The recommendation it means is 150 µg for adults. If you eat gim every day, the lab numbers are easy to check, and a 2025 Korean study of 104 laver samples is the best set I found.

The article is on Daum, a Korean portal. It lists seasoned gim next to miyeokguk (미역국, seaweed soup) at 1,000 to 2,000 µg a bowl, and it gives no per-100 g figure or measurement source, so the 200 to 300 µg has no visible origin.

Title card reading Korean Laver (Gim) Iodine, 100 mg/kg vs 2,432 for kelp, over a photo of gimbap slices on a plate

What 348 seaweed samples measured

Researchers at the National Institute of Fisheries Science in Busan collected seaweed from 12 coastal regions between October 2020 and July 2024, freeze-dried it, and measured iodine by ICP-MS. The paper, Lee et al., Foods, August 2025, reports dry-weight means for five kinds:

Seaweed Samples Mean iodine, mg/kg dry weight
Laver (gim, Porphyra) 104 100.18 ± 78.60
Green laver (파래, Enteromorpha) 76 86.11 ± 59.85
Sea mustard (miyeok, Undaria) 61 176.89 ± 88.91
Hijiki 87 526.57 ± 282.16
Sea tangle (dasima, kelp) 20 2,432.11 ± 1,110.25

The spread inside laver is wide, from 23.45 to 412.19 mg/kg across the 104 samples. Dividing the table's two means, kelp is about 24 times laver by dry weight. The paper's own text says "more than 45 times", and the two figures do not agree with each other. A different Korean paper on brown seaweed, Kwon et al. 2024, cites an earlier total diet study that put sea mustard at seven times and kelp at 80 times laver. The ratio changes with the sample and the preparation. In the table above laver is near the bottom (only green laver is lower), and the total diet study that Kwon cites also puts it below both brown seaweeds.

Grams, not sheets

One mg/kg equals one µg per gram. At the study mean, 1 g of dried laver holds about 100 µg of iodine, and 150 µg arrives at roughly 1.5 g. At the lowest sample (23.45) it takes about 6.4 g to reach 150 µg, and at the highest (412.19) about 0.36 g. I did those three divisions myself; the paper does not give them.

The Daum article's 2 g sheet at 100 µg per gram gives 200 µg, the bottom of its 200 to 300 range. So the claim fits the mean if the sheet really is 2 g of pure laver. A seasoned sheet also carries oil and salt, and I did not weigh one, so the weight on your own packet is the number to trust. Package grams times 100, with 23 to 412 as the range, is the check.

Quote card: 1 g of dried gim is about 100 µg of iodine at the study mean; the adult guideline is 150 µg a day

What Koreans actually eat

The same paper took consumption from the 2023 national nutrition survey (KNHANES). The average person eats 1.02 g of laver a day, dry weight, which comes to 102.44 µg of iodine. Among people who reported eating laver that day, the average was 2.94 g, or 294.69 µg.

Its hazard index divides intake by an upper limit. Against Korea's 2,400 µg limit, laver scores 0.04 for the average person and 0.12 for laver eaters. Against the stricter 600 µg limit the paper takes from EFSA, the Europe food-safety agency, it scores 0.17 and 0.49. Kelp gets 0.68 on the Korean limit and 2.72 on the EFSA one, from an average of 0.67 g of dried kelp a day.

The Daum figure is reasonable arithmetic for a pure 2 g sheet at the mean. On these tables the large numbers come from brown seaweed, since kelp averages 1,632.61 µg a day against laver's 102.44.

A white bowl of miyeokguk, Korean seaweed soup, with rice and side dishes beside it

The soup and the broth

Kwon et al. covered 40,166 people in the 2016 to 2021 surveys and counted only brown seaweed, so gim is outside it. Mean iodine from brown seaweed was 559.16 µg a day, with a 95th percentile of 3,062.07 µg, above the 2,400 µg limit. Kelp broth contributed 347.57 µg a day on average, more than kelp itself (115.58) or sea mustard (96.01). Only 37.6% of people ate any brown seaweed on the survey day, and the authors write that usual intake is probably lower than their mean. They describe that mean as "much lower than the UL."

For new mothers the numbers run higher. A 2021 survey of 1,054 postpartum women found a mean of 2,945.6 µg a day, above the 2,400 µg limit. The authors cite about 1,705 µg of iodine in one 250 mL bowl of miyeokguk.

Dried dark seaweed strands loosely piled on a white background — Photo by Markus Winkler on Pexels

Thyroid data

A 2019 analysis of 6,095 adults from the 2013 to 2015 survey estimated mean iodine intake at 790.1 µg, with 551.0 µg from food. Among women, intake at or above the upper limit went with higher odds of thyroid disease than the lowest-intake group (OR 2.418, 95% CI 1.010 to 5.787). The study is cross-sectional, so it shows an association and not a cause. None of these papers sets a safe number of gim sheets for someone with a thyroid condition.

I searched in Korean and English for official video on seaweed iodine from the Ministry of Food and Drug Safety and the Fisheries Science institute and found none, so this post has no embed.

Do you know the weight of the gim pack in your cupboard, and how often it also goes into soup?

This is a running series, not a one-off post — a new post goes up every day, at around 9am Korea time.

About · Contact · Privacy Policy

Read next: Korean Sweet Potato Types: Bam, Hobak and the Japanese Honey One · Bean Sprout Tails: Trim or Keep? Korean Lab Numbers by Part · Does Perilla Oil Need to Be Refrigerated? Korea's 40-Week Test

Comments

Post a Comment

Popular posts from this blog

Kimchi Without Fish Sauce: What Replaces the Umami

Image
A 2021 study in the journal Foods tested whether tomato could stand in for the fish sauce Korean cooks use in kimchi. The tomato came out ahead. You can read the study yourself here . A hot-water tomato extract measured 33,328 mg/kg of glutamic acid, the compound behind savory umami taste, against 21,032 mg/kg for commercial anchovy fish sauce in the same test, roughly a third less. The tomato version also carried less salt, 1.13% versus 1.87%, and far fewer of the volatile compounds that give fish sauce its funk. It can. You're not chasing a lesser copy of the real thing here. Skipping fish sauce means replacing what it does in two ways. It builds a savory backbone into the paste, and it jumpstarts the fermentation. Why Most Kimchi Isn't Vegan to Begin With If you assumed kimchi was just cabbage, chili, and garlic, you're not alone. You're also not right. Traditional recipes, and most jars on a grocery shelf, lean on jeotgal — salted seafood, usually myeolchi-aekj...
Read more

Kimchi Probiotic Counts by Fermentation Stage

Image
Whether store-bought kimchi is still alive, and whether a jar fermented in the fridge ends up with fewer lactic acid bacteria than one left on the counter, are two questions with published counts behind them. Four papers are collected below, each one with its temperature, its duration and its sample attached. None of these studies measures "probiotics" in any regulated sense, and none of them follows the bacteria past the plate. The unit throughout is the colony-forming unit, one cell alive enough at sampling to grow into a visible colony. From under-ripe to properly sour The World Institute of Kimchi keeps a public explainer page on kimchi lactic acid bacteria , posted 17 May 2024. It puts the early, under-ripe stage at about 100,000 lactic acid bacteria per gram of kimchi, with acidity below 0.3%, and 적숙기 (jeoksukgi), the properly ripened stage, at more than 100 million per gram, with acidity running 0.3–0.8%. A thousandfold difference separates the two stages, and the ...
Read more

Is Kimchi Too Salty? 593 mg of Sodium per 100 g

Image
How much sodium is in kimchi? 593 mg per 100 g. The figure comes from the World Institute of Kimchi (세계김치연구소), the government-funded research institute in Gwangju, and it is the number quoted whenever kimchi gets called a salt bomb. The same page prints a second number right beside it. Potassium, 355 mg. That pairing is the whole argument, and the institute makes it explicitly. Its fact-check card news on kimchi sodium, dated 10 February 2023, sets kimchi's potassium-to-sodium ratio at 1 to 1.7 and puts danmuji, the yellow pickled radish that comes free with your jjajangmyeon, in the row below. Danmuji runs 637 mg of sodium against 42 mg of potassium, so 1 to 15.2. Where 593 mg sits inside a Korean day Those two numbers are not from a national food-composition table. I had assumed they were, until I read the credit line under the table. It points to 서울특별시보건환경연구원, Seoul's municipal public health and environment research institute, and to its 2017 survey of sodium and potas...
Read more