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A new study has found a slightly higher risk of autism spectrum disorder in children born to pregnant people exposed to tap water with high levels of lithium, but experts caution that the finding does not show a direct link between the two.
According to data from the US Centers for Disease Control and Prevention, approximately 1 in 36 children in the US are diagnosed with autism spectrum disorder (ASD) each year.
Scientists still don’t know the exact cause of autism, a developmental disorder. Genetics may be a factor, but some people are also considering possible environmental causes.
Cases may increase, but this is also not clear. 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 a similar increase in cases, but the CDC says the increased number of cases is likely linked to more doctors screening for the condition.
Lithium is an alkali metal that can be found naturally in some foods and groundwater. It is also used in batteries, grease, and air conditioners, as well as in the treatment of bipolar disorder and some blood disorders. According to the US Geological Survey, its levels in drinking water in the US are not controlled.
A new study published Monday in the journal JAMA Pediatrics found a small association between lithium and autism diagnoses in Denmark, where researchers say lithium levels in drinking water are similar to those in U.S. water systems.
Researchers examined a database of people with psychotic disorders born between 2000 and 2013 to find information about 8,842 cases of ASD and 43,864 participants who did not have ASD. They then measured lithium concentrations in 151 public waterworks that served more than half the Danish population and tracked where pregnant people lived in relative terms.
As lithium levels in the water increased, the risk of an ASD diagnosis increased slightly. Specifically, those who had the second and third highest exposures during pregnancy had a 24% to 26% higher risk of ASD, compared to those with the lowest exposure levels. Diagnosis in children. The group with the highest level of risk had a 46% higher risk than the group with the lowest level of risk.
The researchers couldn’t tell how much water the pregnant people drank, but they chose Denmark in part because residents there consume the lowest amount of bottled water in Europe.
Experts say it’s important to note that research can’t show that exposure to lithium directly causes autism.
Further study is needed, said study co-author Dr. Beate Ritz, professor of neurology at the David Geffen School of Medicine at UCLA and professor of epidemiology and environmental health at the UCLA Fielding School of Public Health.
“Any drinking water contaminant that could affect the developing human brain should be thoroughly investigated,” Ritz said in a news release. He said the research would need to be replicated in other countries to find a similar relationship.
According to an editorial published with the study, the implications of the findings are complex as far as public health policy is concerned. Lithium levels in water, concentrations at which studies have linked potential ASD risk, have also been linked to health benefits such as lower rates of hospitalization for psychiatric disorders and suicide.
Dr. David C. Bellinger, professor of neurology and psychology at Harvard Medical School, wrote, “If all of these associations are valid, Solomon’s wisdom will be needed to develop guidelines for lithium in drinking water that are maximally protective for the entire population.” “Until the basic biology of ASD is better understood, it will be difficult to distinguish causal and spurious relationships.”
Dr. Max Wiznitzer, director of the Rainbow Autism Center at University Hospitals Rainbow Babies and Children’s Hospital in Cleveland, points to other research on the effects of lithium on pregnant people who take it for mental health disorders. Those studies – which looked at people exposed to levels much higher than those found in drinking water – showed no association with autism spectrum disorder.
“It’s an interesting relationship, but causation has not been definitively proven,” said Wiznitzer, who was not involved in the new research. “We have to see whether there is a viable and biologically plausible mechanism by which small amounts of lithium in the water supply could somehow do this, yet pharmacological doses of lithium have not been reported to increase the risk of ASD in women with bipolar disorder.”
Other studies have also suggested a link between ASD and environmental exposure to things like pesticides, air pollution, and phthalates. But none of them point to any of these factors as the direct cause of the disorder.
The link between environmental exposures and ASD is difficult to prove, Wiznitzer said. For example, with research showing that increased exposure to air pollution increases the risk of having a child with ASD, one often wonders whether pollution is the determining factor or whether it is just the population that lives in more polluted areas.
“There is a lot of speculation about environmental factors, but how many of them are actually causally linked?” Wiznitzer said. “We are surrounded by a variety of environmental stressors in our everyday lives. We have to figure out how to basically manage them safely, and that’s probably not what’s at the top of our list.”
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