Iodine
I, a trace mineral
A trace mineral the body uses to make thyroid hormones, found in seafood, milk and iodised salt. This page covers only studies in people that measured thinking, memory, mood, stress, sleep, energy or quality of life, where iodine is studied mostly for thinking and development in children and in pregnancy. Here is every one we could find, sorted from each study's summary.
- Found in: seafood, milk and iodised salt
- Most tested: 150 µg a day
- Mostly in pregnancy and childhood
From every paper to the studies that matter
Our search looked only at iodine papers on thinking, mood, sleep and energy, not at all iodine research. Many of those are about iodine contrast for scans or radioactive iodine, which this page leaves out. A smaller share gives iodine to people, and that is what this page is about.
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7,569 papers on iodine and thinking, mood, sleep or energy.Every record in PubMed, all years
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446 are about people.The rest: 2,079 lab and animal studies, 746 reviews, 4,298 on chemistry, farming and more
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24 give iodine on its own.15 more give iodine with iron, vitamins or other nutrients, or as fish
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12 are randomised against a placebo.Randomised controlled trials In a randomised controlled trial, people are put into groups by chance, one taking the treatment and one a placebo or other comparison. Chance spreads differences such as age and health evenly, so a difference between the groups is more likely to be down to the treatment., the strongest kind of study
Bar lengths use a square-root scale so the small numbers stay visible.
How much research there is
- 24 studies giving iodine to people, on thinking, mood, sleep and energy
- 12 of them randomised against a placebo A placebo-controlled trial compares a real treatment with a dummy that looks the same, the placebo. People often feel better when they expect to, so comparing against a placebo shows how much of the change comes from the treatment itself.
- 11,703 people taking part, where studies say
- 77 systematic reviews A systematic review searches for every study on a question in a set, written-down way, judges the quality of each and sums up what they show together. Many include a meta-analysis. The Atlas lists these as pooled reviews. pooling the trials
Studies in people, by year published
Iodine on its own.
What the studies looked at
Each study can measure several things. Choose a topic to see its studies in the list below.
Studies in people with a diagnosed condition are counted here and listed with their population. We describe what they measured, not what they might treat. Most studies also report safety; see below.
What was tested, and how much
Doses are micrograms (µg) of iodine a day, as each study's summary gives it. Many studies gave iodised salt or fortified food, which has no set daily amount, or a single large dose of iodised oil meant to last months, so those have no dot. A few summaries may give the weight of the salt, such as potassium iodide, rather than the iodine itself, so read single dots with care.
Daily amount, one dot per study
Studies per extract
Named extracts are the maker's brand. "Not named" means the study didn't say.
All studies in people
Filter the list, then open a study on PubMed. Each row comes from the study's published summary, and most follow pregnant women, babies or schoolchildren, often in areas low in iodine.
| Study | Who took part | People | Extract and daily dose | Length |
|---|---|---|---|---|
| Mohammed 2021RCT, active or other control | Pregnant women and infants, Ethiopia (iodized salt) | 1,220 | Iodised salt | – |
| Nazeri 2021RCT, placebo | Breastfeeding mothers and children at 36 months | 122 | Not named | – |
| Mohammed 2020RCT, active or other control | Pregnant women and children, Ethiopia | 1,220 | Iodised salt | – |
| Verhagen 2020RCT, placebo | Mildly iodine-deficient pregnant women | 514 | Not named, 200 µg | – |
| Bougma 2018RCT, placebo | Infants in Ethiopia, iodised salt | 1,835 | Iodised salt | – |
| Aboud 2017RCT, active or other control | Preschool children, northern Ethiopia | 1,602 | Iodised salt | – |
| Williams 2017RCT, placebo | Preterm infants under 31 weeks | 1,273 | Sodium iodide | – |
| Gowachirapant 2017RCT, placebo | Mildly iodine-deficient pregnant women | 832 | Potassium iodide, 200 µg | – |
| Zahrou 2016RCT, placebo | Iodine-deficient schoolchildren aged 7-9 | – | Iodine-fortified milk | 39 weeks |
| Brucker-Davis 2015Non-randomised controlled | Euthyroid pregnant women, borderline deficiency | 86 | Not named, 150 µg | – |
| Zhou 2015RCT, placebo | Pregnant women, early pregnancy | 59 | Not named, 150 µg | – |
| Bol'shakova 2014Non-randomised controlled | Young women, iodine insufficiency | 30 | Iodized milk protein, 100 µg | 4 weeks |
| Velasco 2009Non-randomised controlled | Pregnant women and their infants | 194 | Potassium iodide, 300 µg | – |
| Gordon 2009RCT, placebo | Mildly iodine-deficient children aged 10-13 | 184 | Not named, 150 µg | 28 weeks |
| Zimmermann 2006RCT, placebo | Iodine-deficient schoolchildren aged 10-12 | 310 | Iodized oil | 24 weeks |
| Koltun 2005Non-randomised controlled | Schoolchildren in iodine-deficient region | 537 | Iodomarine, 100 µg | – |
| Rakov 2003Non-randomised controlled | Servicemen with iodine deficiency | – | Iodocasein (iodized bread) | 39 weeks |
| O'Donnell 2002Non-randomised controlled | Children of mothers supplemented in pregnancy, Xinjiang | – | Not named | – |
| Huda 2001RCT, placebo | Iodine-deficient schoolchildren, grades 1-2 | 305 | Iodized oil | 17 weeks |
| van den Briel 2000RCT, placebo | Iodine-deficient schoolchildren aged 7-11 | 196 | Not named | 52 weeks |
| Isa 2000Non-randomised controlled | Orang Asli schoolchildren and pregnant mothers, goitre area | – | Iodized oil | – |
| Cao 1994Non-randomised controlled | Children and pregnant women, iodine-deficient area | 984 | Not named | – |
| Pharoah 1991RCT, placebo | Children of mothers supplemented in pregnancy | – | Not named | – |
| Bautista 1982Non-randomised controlled | Goitrous schoolchildren | 200 | Iodized oil | 95 weeks |
What's known about safety
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In trials
A 2026 review of eight trials in children found that none reported side effects of iodine. Daily studies on this page gave 50 to 300 µg, and some gave children one large dose of iodised oil instead. In pregnancy, a review says the safety of extra iodine where intake is only mildly low isn't well researched.
Velasco 2026, Cochrane review of 8 trials in children; Dineva 2020, review of 37 studies in pregnancy; this page's study list
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In the UK
Potassium and sodium iodide and iodate are permitted forms of iodine in food supplements. The NHS says adults need 140 µg a day and that 0.5 mg (500 µg) a day or less from supplements is unlikely to cause harm. The EU upper limit for adults is 600 µg a day from all sources, and lower for children.
Retained Directive 2002/46/EC, Annex II; NHS iodine page; SCF 2002 upper limits as given in BfR opinion 065/2025, Oct 2026
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Check first
High doses taken for a long time can change how the thyroid works, and people whose thyroid has started overworking on its own after years of low iodine, more often older people, are at higher risk. Speak to a pharmacist or doctor first if you have a thyroid condition, or to your midwife or doctor if you're pregnant or breastfeeding.
NHS iodine page; BfR opinion 065/2025 on iodine; Dineva 2020 review
Where these studies come from
We list every published study in people that gave iodine and measured thinking, memory, mood, stress, sleep, energy or quality of life, not all iodine research. Potassium iodide and iodate, iodised salt, iodised oil and Lugol's iodine count. Iodine contrast for scans, radioactive iodine treatment and studies that only measured iodine levels are left out. Iodine given with iron, vitamins or other nutrients, and cod eaten as a food, count as a blend. This first version is built from each study's summary; full-paper checks come next.
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We search
PubMed, the world's main library of medical research, for every paper on L-theanine.
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We keep studies in people
Lab and animal work is counted but left out of the list, because it doesn't tell you what happens in people.
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We note the basics
Who took part, how many, how much and for how long, from each study's published summary. A second check corrects what the first read gets wrong.
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We read them in full
Results appear once we've read the whole paper and checked every number. The date at the top shows when this entry was last updated.
Download the study list
Every study in people as a spreadsheet, 24 rows, free to reuse with a link back.
Versions
Each update to the data gets a new version number, so you can tell what changed and when.
See every version
1.0 · 24 Oct 2026. First release. Every published study giving iodine to people that measured thinking, memory, mood, stress, sleep, energy or quality of life is listed from its summary. None is read in full yet.
