Autism: Study finds slightly higher risk of diagnosis in areas with more lithium in drinking water, but experts say more research is needed


A new study has found a modestly higher risk of autism spectrum disorder in children born to pregnant women exposed to tap water with higher levels of lithium, but experts caution that the link 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 don’t know the exact cause of autism, a developmental disorder. Genetics may be a factor, but some also consider potential environmental causes.

Cases may be increasing, but that too is unclear. A study published this year of cases in the New York-New Jersey area found that the rate of autism diagnosis 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 most likely related to more doctors testing for the condition.

Lithium is a rare earth element that can be found naturally in some foods and groundwater. It is used in batteries, grease and air conditioners, as well as in the treatment of bipolar disorder and some blood disorders. Its levels in US drinking water are not regulated, according to the US Geological Survey.

A new study published Monday in the journal JAMA Pediatrics found a small link between lithium and autism diagnoses 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 for children born between 2000 and 2013 to find information on 8,842 cases of autism disorder and 43,864 participants who did not have autism disorder. They then measured the concentration of lithium in 151 public waterworks that serve more than half of Denmark’s population and noted where pregnant people lived.

As water lithium levels rise, there is a modestly increased risk of an ASD diagnosis. Specifically, compared to those with the lowest level of exposure, those who had the second and third highest exposures during pregnancy had a 24% to 26% higher 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 can’t say how much water the 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 the study can’t show that lithium exposure directly leads to a diagnosis of autism.

Further studies are needed, said study co-author Dr. Beate Ritz, professor of neurology at UCLA’s David Geffen School of Medicine and professor of epidemiology and environmental health at UCLA’s Fielding School of Public Health.

“All drinking water contaminants that can affect the developing human brain deserve intensive study,” Ritz said in a news release. She added that the study would need to be replicated in other countries to look for a similar link.

The implications of the findings are complex in terms of public health policy, according to an editorial published alongside the study. Levels of lithium in water, at concentrations that the study linked to potential risk of ASD, are also associated with health benefits, such as lower rates of hospitalization for psychiatric disorders and suicide.

“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,” wrote David S. Bellinger, Ph.D., professor of neurology and psychology at Harvard Medical School. “Until the underlying biology of ASD is better understood, it will be difficult to distinguish causal from spurious associations.”

Dr. Max Wisnitzer, director of the Rainbow Autism Center at 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 disorders. These studies – which looked at people exposed to much higher levels than those found in drinking water – showed no link to autism spectrum disorder.

“It’s an interesting connection, but causation has definitely not been 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 could somehow do this, but pharmacologic dosing of lithium in women with bipolar disorder has not been reported to cause an increased risk of ASD.”

Other studies have also suggested links 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.

A link between environmental exposures and ASD is difficult to prove, Wiznitzer said. With research showing that increased exposure to polluted air increases the risk of having a child with ASD, for example, he often wonders if pollution is the determining factor or if it’s just that the population lives in more polluted areas.

“There’s a lot of speculation about environmental factors, but how much of it is really causal?” Wiznitzer said. “In our daily lives, we are bombarded with various environmental factors. We have to figure out how to navigate them basically safely, and that’s probably not high on our list.”

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