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

CNN
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A new study has found a moderately increased risk of autism spectrum disorder in children born to pregnant women exposed to tap water containing higher levels of lithium, but experts caution that this association does not show a direct link between the two.

According to data from the U.S. Centers for Disease Control and Prevention, approximately 1 in 36 children in the United States is diagnosed with autism spectrum disorder (ASD) each year.

Scientists still don’t know the exact cause of autism, a developmental disorder. Genetics may be involved, but some are also looking at possible environmental causes.

Cases may be on the rise, but that’s also unclear. A study published this year of cases in the New York-New Jersey area found that autism diagnosis rates tripled in some age groups between 2000 and 2016. A 2021 report found a similar increase in cases, but the CDC says the rise in cases is most likely related to more doctors screening for the condition.

Lithium is an alkali metal 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 lithium levels in drinking water are similar to those in U.S. water systems.

The researchers searched a database of people with psychiatric disorders in children born between 2000 and 2013 to find information on 8,842 cases of ASD and 43,864 participants who did not have ASD. They then measured lithium concentrations in 151 public water systems serving more than half of the Danish population and mapped the pregnant women’s places of residence in relation to these.

As lithium levels in water increased, the risk of ASD diagnosis increased slightly. Specifically, compared with those with the lowest level of exposure, those with the second and third highest exposures during pregnancy had a 24 to 26 percent higher risk of ASD. diagnosed in children. The most exposed group had a 46% higher risk than those with the least exposure.

The researchers couldn’t determine how much water pregnant women drank, but they chose Denmark in part because people there consume one of the lowest amounts of bottled water in Europe.

Experts say it’s important to note that research cannot demonstrate that lithium exposure directly leads to an autism diagnosis.

Further studies are 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 human brain development deserves close scrutiny,” Ritz said in a news release. She added that the research should be replicated in other countries to look for a similar link.

The implications of these findings are complex for public health policy, according to an editorial published alongside the study. Lithium levels in water, at concentrations that the study associates with a potential risk for ASD, have also been associated with health benefits, such as lower rates of hospitalization for psychiatric disorders and suicide.

“If all of these associations are valid, the wisdom of Solomon will be needed to develop guidelines for lithium in drinking water that are maximally protective for the entire population,” wrote Dr. David C. Bellinger, professor of neurology and psychology at Harvard Medical School. “Until the basic biology of ASD is better understood, it will be difficult to distinguish causal associations from spurious ones.”

Dr. Max Wiznitzer, director of the Rainbow Autism Center at Rainbow Babies and Children’s Hospital in Cleveland, cites other research on the effects of lithium on pregnant women who take it for mental health conditions. Those studies, which involved people exposed to levels far higher than those found in drinking water, showed no link to autism spectrum disorders.

“It’s an interesting association, but causality is not definitively proven,” said Wiznitzer, who was not involved in the new study. “We need to see if there’s a viable, biologically plausible mechanism by which a small amount of lithium in the water supply can somehow cause this, but pharmacological dosing of lithium in women with bipolar disorder has not been reported to increase the 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 pinpoint these factors as the direct cause of the disorder.

It’s difficult to prove a link between environmental exposure and ASD, Wiznitzer said. With research showing that increased exposure to air pollution increases the risk of giving birth to a child with ASD, for example, he often wonders whether pollution is the driving factor or whether it’s just populations that live in more polluted areas.

“There’s a lot of speculation about environmental factors, but how many of them are actually causally related?” Wiznitzer said. “We’re bombarded with a variety of environmental stressors in our daily lives. We have to figure out how to manage them safely, and this one is probably not at the top of our list.”