According to Gram Research analysis, a 2026 cross-sectional study of 9,443 American adults found that moderate iodine levels—specifically between 67.7 and 121.2 micrograms per liter in urine—were associated with increased kidney stone risk. The relationship was nonlinear, meaning kidney stone risk peaked at a specific iodine level rather than increasing steadily with more iodine. However, this study shows association, not proof of cause-and-effect, so people shouldn’t drastically change iodine intake without consulting their doctor.
A large study of over 9,400 Americans found that certain levels of iodine in the body may be linked to kidney stone formation. Researchers analyzed data from the National Health and Nutrition Examination Survey between 2007 and 2018, measuring iodine levels through urine tests. The study discovered that people with moderate iodine levels—specifically between 67.7 and 121.2 micrograms per liter—showed an association with kidney stones. However, the relationship wasn’t straightforward; it followed a curved pattern rather than a simple line. This finding could help doctors better understand kidney stone risk factors and guide dietary recommendations for iodine intake.
Key Statistics
A 2026 cross-sectional analysis of 9,443 American adults from the National Health and Nutrition Examination Survey found that urine iodine levels between 67.7 and 121.2 micrograms per liter were associated with increased kidney stone risk.
Research reviewed by Gram found that kidney stone risk peaked at a urine iodine concentration of 134.9 micrograms per liter, following a nonlinear relationship rather than a simple straight-line pattern.
The 2026 study of over 9,400 participants showed that both very low and very high iodine levels had lower kidney stone risk compared to moderate iodine levels, suggesting a specific problematic range rather than a simple dose-response relationship.
The Quick Take
- What they studied: Whether the amount of iodine in a person’s body affects their chances of developing kidney stones
- Who participated: 9,443 American adults aged 20 to 60 years who participated in a national health survey between 2007 and 2018
- Key finding: People with moderate iodine levels (67.7-121.2 μg/L in urine) showed a connection to kidney stone formation, though the relationship was not a simple straight line
- What it means for you: If you’re prone to kidney stones, monitoring iodine intake may be worth discussing with your doctor. However, this is one study showing association, not proof of cause-and-effect, so don’t drastically change your diet without medical guidance
The Research Details
Researchers examined health information collected from thousands of Americans as part of the National Health and Nutrition Examination Survey, a large government health study. They looked at data gathered between 2007 and 2018 from 9,443 adults aged 20 to 60 years. To measure iodine levels, scientists tested participants’ urine samples and divided people into four groups based on their iodine concentration. They then compared kidney stone rates across these groups to see if there was a pattern.
The researchers used advanced statistical methods to look for connections between iodine levels and kidney stones. They created curved graphs to show how the relationship changed at different iodine levels, rather than assuming a simple straight-line relationship. This approach helped them identify a specific “sweet spot” where kidney stone risk appeared highest—around 67.7 to 121.2 micrograms per liter of urine.
To make sure their findings were solid, the team ran additional tests using different statistical approaches. These sensitivity analyses confirmed that their main conclusions held up even when they adjusted their methods slightly.
This research approach matters because kidney stones affect millions of people and cause significant pain and medical costs. Understanding what dietary factors contribute to kidney stone formation could help people prevent them. By studying a large, representative sample of the American population rather than just people in a doctor’s office, researchers could see patterns that might apply to the general public. The nonlinear relationship they found is particularly important—it suggests that more iodine isn’t always worse, and that a specific range may be most problematic.
This study has several strengths: it included a large, nationally representative sample of over 9,400 people, used objective measurements of iodine through urine testing, and applied rigorous statistical methods. However, because it’s a cross-sectional study (a snapshot in time), it can show associations but cannot prove that iodine causes kidney stones. The study also relied on dietary recall data, which can be imperfect. Additionally, the researchers couldn’t account for all possible factors that might influence kidney stone formation, such as family history or certain medications.
What the Results Show
The study revealed that kidney stone risk followed a curved pattern based on iodine levels rather than increasing steadily. The highest risk appeared at a urine iodine level of approximately 134.9 micrograms per liter, with the concerning range being 67.7 to 121.2 micrograms per liter. Interestingly, both very low and very high iodine levels showed lower kidney stone risk compared to this moderate range.
When researchers divided participants into four groups based on iodine levels, they found statistical differences in kidney stone prevalence across groups. The relationship was complex—it wasn’t simply “more iodine equals more stones.” Instead, there appeared to be a specific window where kidney stone risk peaked, then decreased at higher levels.
The findings held up when researchers performed additional analyses to check their work. They tested different statistical models and adjusted for various factors that could influence kidney stone formation, and the pattern remained consistent. This consistency suggests the finding is likely reliable rather than a random result.
The study confirmed that the relationship between iodine and kidney stones is nonlinear, meaning it doesn’t follow a simple straight-line pattern. This is important because it suggests that simply reducing iodine intake might not be the answer for everyone—the relationship is more nuanced. The inflection point at 134.9 μg/L represents the peak risk level, which could serve as a reference point for future research and clinical recommendations.
This is one of the first large-scale studies to examine the specific relationship between dietary iodine intake and kidney stone formation in a representative U.S. population. Previous research has identified many kidney stone risk factors including calcium, sodium, and fluid intake, but iodine has received less attention. This study adds iodine to the list of dietary factors worth considering, though more research is needed to understand how it compares in importance to other known risk factors.
This study shows association, not causation—meaning we can’t say that iodine definitely causes kidney stones, only that they appear together in some cases. The research is a snapshot in time, so it can’t track whether changes in iodine intake actually lead to kidney stone development. The study relied on single urine measurements, which may not perfectly represent someone’s typical iodine intake. Additionally, researchers couldn’t account for all possible factors affecting kidney stones, such as genetic predisposition, medications, or detailed medical history. The findings apply best to adults aged 20-60 and may not apply to children or elderly people.
The Bottom Line
Based on this research, people with a history of kidney stones should discuss iodine intake with their healthcare provider. This doesn’t mean avoiding iodine entirely—it’s an essential nutrient needed for thyroid health—but rather finding an appropriate balance. For the general population without kidney stone history, no changes to iodine intake are recommended based on this single study. Anyone considering dietary changes should consult their doctor, especially if they have kidney disease or a family history of kidney stones. Confidence in these recommendations is moderate, as this is one observational study that shows association rather than definitive cause-and-effect.
People who have had kidney stones or have a family history of them should be most interested in this research. Those with thyroid conditions requiring iodine supplementation should discuss this study with their doctor. The general population without kidney stone risk factors doesn’t need to change their iodine intake based on this single study. Healthcare providers treating kidney stone patients may find this information useful for counseling.
If someone were to adjust their iodine intake based on this research, changes in kidney stone risk would likely take months to become apparent, as kidney stone formation is a gradual process. This isn’t something where you’d expect immediate results. However, this study doesn’t provide enough evidence to recommend making changes in the first place without medical guidance.
Frequently Asked Questions
Does iodine cause kidney stones?
This study found an association between moderate iodine levels and kidney stones, but doesn’t prove iodine causes them. The relationship appears nonlinear, with peak risk at 134.9 μg/L of urine iodine. More research is needed to understand the actual cause-and-effect mechanism.
Should I reduce my iodine intake to prevent kidney stones?
Not without consulting your doctor. Iodine is essential for thyroid health. If you have kidney stone history, discuss iodine intake with your healthcare provider, who can help you find an appropriate balance based on your individual risk factors.
What iodine level is safe for kidney stone prevention?
This study suggests levels below 67.7 or above 121.2 micrograms per liter showed lower kidney stone risk. However, individual needs vary based on thyroid health and other factors. Your doctor can help determine the right iodine level for you.
Which foods have the most iodine?
Iodized salt, seafood, dairy products, and eggs are primary iodine sources. Seaweed contains very high amounts. If concerned about kidney stones, track these foods and discuss your intake with your healthcare provider.
Can I get kidney stones from eating too much salt?
Salt itself isn’t the main culprit, but high sodium intake can increase calcium in urine, raising kidney stone risk. This study focuses on iodine specifically, which is added to table salt. Reducing overall salt intake may help prevent kidney stones.
Want to Apply This Research?
- Track daily iodine intake in micrograms by logging iodized salt use, seafood consumption, dairy products, and eggs. Note any kidney stone symptoms or urinary changes to identify personal patterns.
- For users with kidney stone history, use the app to monitor iodine-containing foods and maintain a log of intake levels. Set reminders to discuss iodine intake with a healthcare provider and track any correlations with kidney discomfort or urinary symptoms.
- Create a monthly report comparing iodine intake levels with any kidney-related symptoms or medical visits. Share this data with your healthcare provider to identify personal risk patterns and adjust dietary recommendations accordingly.
This research shows an association between iodine levels and kidney stones but does not prove causation. The findings apply to adults aged 20-60 and may not apply to children, elderly people, or those with certain medical conditions. Anyone with a history of kidney stones, thyroid disease, or kidney disease should consult their healthcare provider before making dietary changes related to iodine intake. This article is for informational purposes only and should not replace professional medical advice. Do not change your diet or supplement use based solely on this study without guidance from your doctor.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.