Higher Lithium Levels in Drinking Water May Be Linked to a Rare Heart Condition in Children, Study Finds

Lithium is familiar as a psychiatric medication, but it also occurs naturally in groundwater. Now researchers at the University of California, San Francisco have found a possible connection between lithium levels in local water sources and Wolff-Parkinson-White syndrome, or WPW, a rare heart rhythm condition present from birth.

In California counties with the highest lithium concentrations, children were more likely to have a WPW diagnosis.

The finding comes from a study involving millions of medical records, giving researchers an unusually broad look at a condition many families may never have heard of. Still, the most important question remains unanswered.

Is lithium involved in the development of the condition, or are water measurements tracking something else entirely?

That distinction matters because the study can identify a pattern without establishing what caused it. And while one percentage from the findings is especially striking, the actual number of children affected tells another important part of the story.

What A 71% Jump Does And Doesn’t Mean

The study, published October 13 in The Journal of Clinical Investigation, examined records for more than 2.3 million California children under 18.

Their first hospital, emergency-department, or ambulatory-surgery visits occurred between 2016 and 2020. Researchers then matched those records with county-level groundwater and surface-water lithium measurements collected from 1998 through 2020.

County averages ranged from 1.49 to 213 parts per billion, with a median of 12.5 ppb. Children in the highest-exposure counties (levels at or above 32.6 ppb) had 71% higher unadjusted odds of a WPW diagnosis than children in lower-exposure counties.

After accounting for age, sex, race, ethnicity, insurance, and income, the increase was 60%.

Yet only 686 children had a documented WPW diagnosis. That represents just 0.03% of the 2.3 million children studied. The percentage increase sounds dramatic, but the condition remained rare even in counties with higher lithium levels.

Related: The Dark Reality of Chemical Warfare: 10 Disturbing Ways It Touches Our Daily Lives

Why Researchers Looked In The Water

The idea grew out of what doctors already knew about lithium as a medicine.

Earlier research had associated lithium medication during pregnancy with a higher risk of congenital heart defects, including Ebstein’s anomaly. That condition often involves extra electrical pathways in the heart, raising a question for the UCSF team: Could much lower levels of naturally occurring lithium have a similar association?

WPW involves an extra strand of heart muscle that develops before birth. It creates an abnormal electrical connection between the heart’s upper and lower chambers, which can trigger supraventricular tachycardia, a rapid heartbeat that can cause palpitations or fainting.

The condition also carries a small increased risk of sudden death. However, doctors can eliminate the responsible tissue through a minimally invasive procedure called catheter ablation.

What remains puzzling is why those extra pathways develop in the first place. Most people who have them report no family history, making environmental influences worth investigating.

Gregory Marcus, the study’s senior author and a UCSF cardiology professor, explained the mystery: “We’ve known about these pathways for decades, and we know how to treat them, but we haven’t known why people develop them.”

New York Backed It Up, With A Twist

To see whether the California findings held elsewhere, researchers examined records for more than 1.9 million New York patients from 2010 through 2012.

At lithium exposure levels above 10 ppb, New York showed 22% higher adjusted odds of WPW. At that same level, California showed a 33% increase.

But the results didn’t line up perfectly. At the higher threshold of 32.6 ppb, the New York association was not statistically significant. That difference makes it difficult to identify a consistent exposure level at which the association begins.

The California analysis also linked higher lithium concentrations with diagnoses of supraventricular tachycardia, palpitations, fainting, and congenital heart disease. Those conditions aren’t specific to WPW, however.

Despite earlier interest in Ebstein’s anomaly, an exploratory analysis found no statistically significant association between that condition and lithium exposure.

That 10 PPB Number Isn’t A Legal Limit

It keeps showing up next to this research, and it’s easy to read as a safety line.

The Environmental Protection Agency has no enforceable standard or health advisory for lithium in drinking water. Its 10 micrograms-per-liter health reference level is a screening benchmark derived from effects observed in patients taking lithium as medication.

A measurement above that level doesn’t automatically mean a family faces a known risk. Likewise, a reading below it doesn’t guarantee safety.

Under its Fifth Unregulated Contaminant Monitoring Rule, the EPA required certain public water systems to test for lithium between 2023 and 2025. The agency has since released the final dataset.

That monitoring program gathers information about substances without federal drinking-water limits. Requiring tests doesn’t mean the EPA has determined that lithium in tap water is dangerous.

What The Study Couldn’t Measure

The biggest gap sits between a county’s water and one child’s pregnancy.

Researchers knew the average lithium concentrations in county water sources, but not how much lithium individual children or their mothers actually encountered during pregnancy.

The county of residence therefore served as a proxy for personal exposure. And because families can move, the main analysis assumed children remained in their county of birth. Researchers ran additional sensitivity checks involving children under one and under two to examine that assumption.

Other explanations remain possible. Genetics or other environmental factors could explain some or all of the observed association. Even a current household water test wouldn’t reveal what a mother encountered years earlier during pregnancy.

In UCSF’s announcement of the study, Marcus said the findings shouldn’t alarm people about drinking-water safety, including pregnant people.

He described the result as an exciting step toward identifying an environmental factor that might be modified. But whether lithium actually contributes to WPW remains unresolved.

The next challenge is determining how much exposure matters, and at what stage of development. That will require more precise measurements and further investigations across different states, countries, and water systems.

Meanwhile, the EPA’s newly released nationwide monitoring data offers another resource for examining lithium in drinking water. Whether those measurements eventually contribute to a formal federal health evaluation remains an open question.

If your water utility posted its lithium results tomorrow, what would you want it to tell you alongside the numbers?

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