Children living in areas with higher levels of lithium in drinking water were more likely to be diagnosed with Wolff-Parkinson-White syndrome, a rare heart condition that can cause a dangerously fast heartbeat, according to a new study led by UC San Francisco researchers.
The findings, which were published online in The Journal of Clinical Investigation, are based on health and water-quality data for more than 2.3 million children in California and were also observed among nearly 2 million children in New York. Children in California counties with lithium levels in the highest 25% had 71% greater odds of a Wolff-Parkinson-White (WPW) diagnosis than those living in counties with lower levels.
Lithium occurs naturally in groundwater, and concentrations vary widely by location. Although the research focused on California and New York, lithium is found in groundwater used for drinking water across the U.S. and elsewhere, raising questions about the potential broader public health significance of the findings.
WPW occurs when an extra strand of heart muscle, known as an accessory pathway, creates an abnormal electrical connection in the heart. These pathways form during fetal development, but why they develop has remained largely unknown. Most people with accessory pathways do not have a family history of the condition, suggesting that environmental exposures during fetal development could play a role.
"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."
Changes in the developing heart
Accessory pathways are among the most common causes of supraventricular tachycardia (SVT), a rapid heart rhythm that can cause palpitations and other symptoms. WPW, which involves a particular type of accessory pathway, is also associated with a small increased risk of sudden death.
The pathways can be treated with catheter ablation, a minimally invasive procedure that eliminates the small area of heart tissue responsible for the abnormal electrical connection.
Medicinal doses of lithium during pregnancy have been associated with an increased risk of congenital heart defects, including Ebstein's anomaly, a rare condition that is frequently accompanied by accessory pathways. That led the UCSF researchers to ask whether lithium in drinking water might also be associated with changes in the developing heart.
In addition to the association with WPW, higher lithium levels in California were associated with SVT, palpitations, and fainting. Researchers then retested their main finding in New York, where children living in areas with lithium levels above 10 parts per billion also had greater odds of WPW.
How environmental factors may affect health
We're exposed to things in our environment every day, including substances that occur naturally.
Gregory Marcus, MD, MAS
The study does not prove that lithium causes WPW. Researchers did not know how much lithium individual children or their mothers consumed, and they used county of residence to estimate exposure. Other environmental or genetic factors could also help explain the association.
Marcus said the findings should not alarm people about the safety of their drinking water, including those who are pregnant. WPW is rare: Just 686 of the more than 2.3 million California children in the study had a documented diagnosis.
Instead, researchers said the results underscore the importance of collecting environmental data and studying how ordinary environmental factors 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 U.S., although the U.S. Environmental Protection Agency requires monitoring for it through its program for unregulated contaminants. The U.S. Geological Survey also measures lithium in groundwater.
Researchers said studies in other populations, as well as research that more precisely measures exposure during pregnancy, are needed to determine whether lithium plays a causal role.
"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."
Authors: In addition to Marcus, the study authors are Justin T. Teraoka, Anushree Agarwal, Janet J. Tang, and Thomas A. Dewland, all of UC San Francisco.
Disclosures: The authors declared no conflicts of interest.
