What do the states mean?+
- Solid: well studied, and it works.
- Half-there: the science is still forming.
- A ghost: almost no real studies.
- Hollow: well studied, and it does not work.
- A cord: the pair itself has been tested together.
- Air: nobody has ever tested this pair.
The full scoring method: How we score
Iodine benefits: where the science stands
For thyroid: not settled yet.
Thyroid is what most people take iodine for, and the best studies disagree: three found it helps, two found no effect. As of August 2026, the verdicts on this page rest on evidence from 55 trials, drawn from the strongest research among the 2,349 papers on PubMed that mention iodine. Every claim is checked below.
2,349 papers on PubMed · evidence from 55 trials · 1 caution
Claim by claim
- ThyroidThe science is still forming. The best studies disagree.
- CholesterolThe science is still forming. Results lean positive, but there is not much yet.
- Immunity and coldsThe science is still forming. No real difference found so far.
- JointsThe science is still forming. No real difference found so far.
See 1 more scored claim+
- Memory and focusWell studied, and it does not work. The biggest review covered 2 trials.
Pairs people ask about
The 14 sources we read
- 1993Randomized trial · 54 people · benefit for thyroidsource
- 1999Randomized trial · 617 people · no clear effect on immunity and coldssource
- 2003Randomized trial · 324 people · no clear effect on jointssource
- 2004Meta-analysis · no clear effect on memory and focus; benefit for thyroidsource
- 2006Randomized trial · 310 people · benefit for memory and focussource
- 2009Randomized trial · 184 people · small benefit for memory and focussource
- 2011Randomized trial · 30 people · no clear effect on thyroidsource
- 2015Randomized trial · 163 people · small benefit for cholesterol; benefit for thyroidsource
- 2019Meta-analysis · pools 2 trials, 1,394 people · no clear effect on memory and focussource
- 2019Observational study · 6,180 people · no clear effect on memory and focussource
- 2020Randomized trial · 514 people · no clear effect on memory and focussource
- 2022Randomized trial · 94 people · no clear effect on memory and focussource
- 2024Meta-analysis · pools 18 trials · no clear effect on thyroidsource
- 2024Observational study · 1,203 people · no clear effect on memory and focussource
Chosen as the strongest evidence out of 2,349 papers on PubMed. Every row links to its paper.
Fair questions
Does iodine work?+
For thyroid, it is not settled. The best studies disagree.
Is iodine safe?+
One caution is recorded: What the research mostly asks is whether correcting a shortage helps: trials in populations that were deficient, and supplementation in pregnancy. Very little of it asks whether extra iodine helps someone who already gets enough, so this page cannot answer that question.
Why only 14 sources, when PubMed lists 2,349?+
The 2,349 is every paper that mentions iodine in any way: animal studies, blood measurements, papers where it is a side note. The strongest sources are combined reviews, and each one already gathers every trial its authors could find. Our 14 cover 55 trials between them, and every one is linked above. Both counts are measured, not estimated.