A new study found a moderately increased risk of autism spectrum disorder in children born to pregnant people exposed to tap water with higher levels of lithium, but experts caution that this association does not show a direct link between the two.
About 1 in 36 children in the U.S. is diagnosed with autism spectrum disorder (ASD) each year, according to data from the U.S. Centers for Disease Control and Prevention.
Scientists still do not know the exact cause of autism, a developmental disorder. Genetics may be a factor, but some have also been looking at possible environmental causes.
Cases may be increasing, but that is not clear either. A study published this year on cases in the New York-New Jersey area found that autism diagnosis rates tripled among certain age groups between 2000 and 2016. A 2021 report found similar increases in cases, but the CDC They say the increase in the number of cases is most likely related to more doctors screening for the condition.
Lithium is an alkali metal that can be found naturally in some foods and groundwater. It is used in batteries, greases and air conditioners, as well as in the treatment of bipolar disorder and some blood disorders. Its levels in U.S. drinking water are not regulated, according to the U.S. Geological Survey.
A new study, published Monday in the journal JAMA Pediatrics, found a small association between lithium and autism diagnosis in Denmark, where researchers say the level of lithium in drinking water is similar to that in American water systems. .
The researchers checked a database of people with psychiatric disorders in children born between 2000 and 2013 to find information on 8,842 ASD cases and 43,864 participants who did not have ASD. They then measured the lithium concentration in 151 public water supply facilities that served more than half of the Danish population and mapped where pregnant people lived in relation.
As lithium levels in the water increased, there was a modest increase in the risk of ASD diagnosis. Specifically, compared to people at the lowest exposure level, those who had the second and third highest exposures during pregnancy had a 24% to 26% increased risk of ASD. diagnosed in children. The group with the highest exposure had a 46% higher risk than those with the lowest level of exposure.
The researchers couldn’t determine how much water pregnant women drank, but they chose Denmark in part because residents there consume some of the lowest amounts of bottled water in Europe.
Experts say it’s important to note that research cannot prove that lithium exposure directly leads to an autism diagnosis.
More studies are needed, said study co-author Dr. Beate Ritz, a professor of neurology at the UCLA David Geffen School of Medicine and a professor of epidemiology and environmental health at the UCLA Fielding School of Public Health.
“Any contaminant in drinking water that could affect the developing human brain deserves intense scrutiny,” Ritz said in a news release. He added that the research would need to be replicated in other countries to look for a similar connection.
The implications of the findings are complex when it comes to public health policy, according to an editorial published alongside the study. Lithium levels in water, at concentrations that the study associated with a potential risk of ASD, have also been linked to health benefits, such as lower rates of hospitalization for psychiatric disorders and suicide.
“If all of these associations are valid, it will take the wisdom of Solomon to develop guidelines for lithium in drinking water that maximally protect the entire population,” wrote Dr. David C. Bellinger, a professor of neurology and psychology at Harvard. . Medicine School. “Until the basic biology of ASD is better understood, it will be difficult to distinguish causal from spurious associations.”
Dr. Max Wiznitzer, director of the Rainbow Autism Center at Rainbow Babies University Hospitals and Children’s Hospital in Cleveland, points to other research on the effects of lithium on pregnant people who take it to treat mental health disorders. Those studies, which look at people exposed to levels much higher than those found in drinking water, show no connection to autism spectrum disorder.
“It’s an interesting association, but causality is definitely not proven,” said Wiznitzer, who was not involved in the new research. “We need to see if there is a viable and biologically plausible mechanism by which a small amount of lithium in the water supply can somehow do this, however, pharmacological dosing of lithium in women with bipolar disorder has not been reported cause an increased risk of ASD.”
Other studies have also suggested connections between ASD and environmental exposure to pesticides, air pollution, and phthalates. But none of them point to any of these factors as a direct cause of the disorder.
It’s difficult to prove a link between environmental exposure and ASD, Wiznitzer said. As research shows that increased exposure to air pollution increases the risk of giving birth to a child with ASD, for example, it is often asked whether pollution is the determining factor or whether it is just the populations living in areas more contaminated.
“There is a lot of speculation about environmental factors, but how many of them are actually causally associated?” Wiznitzer said. “We are bombarded with a variety of environmental stressors in our daily lives. “We have to figure out how to basically navigate them safely, and this is probably not one of the first on our list.”