A huge American study involving more than 2.3 million children has identified that a very common trace element indrinking water appears to be associated with a rare congenital heart defect, sometimes responsible for extremely rapid beats. Enough to question the safety of tap water, while requiring us to remain very careful when interpreting these figures.
UC San Francisco researchers observed that children living in counties where water contains the most
lithium were 71% more likely to be diagnosed with
Wolff-Parkinson-White syndrome (WPW). This disease remains very rare: 686 cases for more than 2.3 million children.
What the study shows on lithium and Wolff-Parkinson-White syndrome
In this ecological study in California, Justin T. Teraoka and his colleagues crossed the levels of lithium
in each county’s water with hospital diagnoses of children under 18 years of age. In areas above the 75th percentile, children had 71% greater risk of a WPW diagnosis compared to counties at lower risk.
A validation analysis of nearly 2 million New York children showed a comparable trend. WPW appears when, during fetal life, an additional electrical pathway is created between the atria and ventricles, generally treatable by catheter ablation. Medicinal doses of lithium during pregnancy are already linked to cardiac malformations, including Ebstein’s anomaly frequently accompanied by accessory pathways.
An association to be interpreted with caution, from the American tap to French waters
The authors point out that their work does not prove a direct effect of lithium nor that tap water causes WPW: they did not know the amount of water drunk per child and used the county as a proxy. “This is an exciting step because it points to a potential, possibly modifiable, environmental factor, but we need more research to determine whether lithium actually contributes to their development.” explained Gregory Marcus, a cardiologist at UC San Francisco.
Fortunately, WPW remains exceptional: in the Californian cohort, 0.03% of children received this diagnosis. In France, Ineris reports lithium levels in tap water of up to 171 micrograms per liter depending on the region and specifies that these figures, at this stage, do not allow us to conclude that there is a health risk. There are currently no environmental quality standards specific to lithium.
Should we be concerned about lithium in tap water?
Despite these results, the authors do not recommend changing your water consumption habits, even during pregnancy. Gregory Marcus recalls: “We are exposed to elements of our environment every day, including substances that occur naturally“.
For the cardiologist, the challenge is to better measure these exposures and to link the levels of lithium
to the consequences on health. The next step will be to track the exposure of pregnant women and their babies, then check whether WPW is more common in the most exposed children. Repeated palpitations or unexplained discomfort in a child always warrant medical advice.