Children living in areas with elevated lithium levels in drinking water face higher odds of being diagnosed with Wolff-Parkinson-White syndrome, a rare heart rhythm disorder. Researchers at University of California, San Francisco analyzed health and water data from millions of young patients in California and New York.
County Water Analysis in California and New York
The study, published in The Journal of Clinical Investigation, investigated health records for more than 2.3 million children in California whose first hospital, emergency department, or ambulatory surgery encounter was recorded between 2016 and 2020. Researchers matched these patient records with water-quality data.
Lithium occurs naturally in groundwater, with concentrations fluctuating widely depending on geographic location. Across California counties, average lithium concentrations in water sources ranged from 1.49 parts per billion to 213 parts per billion, with a median of 12.5 parts per billion. Out of the millions of young patients examined in the California dataset, exactly 686 children received a documented diagnosis of Wolff-Parkinson-White syndrome.
Statistical Odds of Wolff-Parkinson-White Diagnoses
Children residing in California counties with lithium levels sitting in the top 25th percentile—representing concentrations at or above 32.6 parts per billion—faced 71 percent greater odds of a Wolff-Parkinson-White diagnosis before adjustment, and 60 percent higher odds after adjustment. When evaluating a broader threshold, children in areas with lithium concentrations at or above the 10 parts per billion health-based screening level experienced 33 percent higher adjusted odds of the diagnosis.
To test external validity, the team examined an independent dataset covering nearly 2 million children in New York. In New York, living in areas with lithium concentrations exceeding 10 parts per billion was associated with a 22 percent increase in the adjusted odds of a Wolff-Parkinson-White diagnosis. However, the association at the 32.6 parts per billion threshold did not reach statistical significance in the New York population.
Accessory Pathways and Related Heart Rhythms
Wolff-Parkinson-White syndrome occurs when an extra strand of heart muscle forms an accessory pathway, creating an abnormal electrical connection between the upper and lower chambers of the heart. These pathways develop during fetal life and represent one of the leading causes of supraventricular tachycardia, a rapid heart rhythm that triggers palpitations, fainting, and other symptoms. While these accessory pathways carry a small, rare risk of sudden death, they are treatable via catheter ablation, a minimally invasive procedure that eliminates the rogue electrical connection.
In addition to diagnosing Wolff-Parkinson-White syndrome, the California analysis identified correlations between higher water lithium levels and related clinical presentations. Children in high-exposure counties exhibited greater odds of supraventricular tachycardia, syncope, and palpitations, though researchers noted that these symptoms are not exclusively tied to accessory pathways.
Scientific Limitations and Environmental Regulation
The observational design means the study establishes an association rather than a direct causal link. Researchers did not track individual water consumption or measure maternal exposure during pregnancy, relying instead on county of residence as a proxy. Furthermore, lithium in drinking water is not currently regulated in the United States, although the U.S. Environmental Protection Agency requires monitoring for it through its program for unregulated contaminants.
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.
Gregory Marcus, UC San Francisco
Study authors emphasized that the findings should not alarm people about the safety of their drinking water, including those who are pregnant, noting that Wolff-Parkinson-White syndrome remains rare. Investigators plan to conduct more precise exposure studies to clarify whether environmental lithium actively directs heart tissue development.