The water we drink may hold clues to a rare heart condition in children, but whether naturally occurring lithium plays a role in its development remains unknown.
A dangerously fast heartbeat can begin with an extra strand of heart muscle that forms before birth. The strand creates an abnormal electrical connection, allowing the heart’s rhythm to go awry. Doctors can eliminate these connections, but a larger question has remained largely unanswered. Why do they develop in the first place?
A study led by UC San Francisco researchers points to a possible environmental clue in drinking water. Children living in areas with higher levels of naturally occurring lithium were more likely to be diagnosed with Wolff-Parkinson-White syndrome, or WPW, a rare condition involving a particular type of abnormal connection. The findings, published online in The Journal of Clinical Investigation, show an association, but do not establish that lithium causes the condition.
These connections, known as accessory pathways, usually occur in people with no family history of the condition. That suggests environmental exposures during fetal development could play a role. Lithium attracted the researchers’ attention because medicinal doses taken during pregnancy have been associated with an increased risk of congenital heart defects, including Ebstein’s anomaly. This rare defect is frequently accompanied by accessory pathways, prompting the team to investigate whether lithium in drinking water might also be associated with changes in the developing heart.
Higher lithium, greater odds of WPW
The researchers analyzed health and water-quality data for more than 2.3 million children in California. Just 686 had a documented WPW diagnosis. Children living in counties with lithium levels in the highest 25% had 71% greater odds of a diagnosis than those in counties with lower levels.
The team then tested its main finding among nearly 2 million children in New York. There, children living in areas with lithium levels above 10 parts per billion also had greater odds of a WPW diagnosis.
Higher lithium levels in California were also associated with palpitations, fainting, and supraventricular tachycardia, or SVT, a rapid heart rhythm that can cause palpitations and other symptoms. Accessory pathways are among the most common causes of SVT. WPW is also associated with a small increased risk of sudden death. Doctors can treat accessory pathways with catheter ablation, a minimally invasive procedure that eliminates the small area of heart tissue responsible for the abnormal electrical connection.
“We’ve known about these pathways for decades, and we know how to treat them, but we haven’t known why people develop them,” said Gregory Marcus, MD, MAS, an endowed professor in atrial fibrillation research in the UCSF Division of Cardiology and senior author of the study. “This is an exciting step because it points to a potential environmental factor that may be modifiable. But we need more research to determine whether lithium is actually contributing to their development.”
Individual lithium exposure remains unknown
The study estimated exposure from the county of residence. Researchers did not know how much lithium individual children or their mothers consumed, and other environmental or genetic factors could help explain the association. Studies in other populations and research that measures exposure during pregnancy more precisely are needed to determine whether lithium plays a causal role.
Marcus said the findings should not alarm people about the safety of their drinking water, including those who are pregnant. Despite the association, WPW was rare in the children studied.
Lithium occurs naturally in groundwater, and its concentration varies widely by location. Groundwater used for drinking water across the United States and elsewhere contains lithium, raising questions about the findings’ potential public health significance beyond California and New York. The researchers said the results underscore the value of collecting environmental data to understand how ordinary exposures may affect health.
“We’re exposed to things in our environment every day, including substances that occur naturally,” Marcus said. “The more precisely we can measure those exposures and connect them with health outcomes, the better we can understand what may be influencing health.”
Lithium in drinking water is not currently regulated in the United States, although the U.S. Environmental Protection Agency requires monitoring through its program for unregulated contaminants. The U.S. Geological Survey also measures lithium in groundwater.
“The next step is to determine whether lithium itself is contributing to the development of these pathways and, if so, how much exposure matters and when during development it matters most,” Marcus said. “That will require studies that can measure exposure much more precisely.”
Reference: “Elevated lithium levels in drinking water are associated with higher prevalence of Wolff-Parkinson-White diagnoses” by Justin T. Teraoka, Anushree Agarwal, Janet J. Tang, Thomas A. Dewland and Gregory M. Marcus, 13 October 2026, The Journal of Clinical Investigation.
DOI: 10.1172/JCI205020
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