Photo: Sean Gallup (Getty Images)

There are few things that can set off the paranoid-minded faster than talking about fluoride in the drinking water. But a new study out Thursday cautiously suggests that even low levels of fluoride in teens could be linked to changes in their kidney and liver function. It’s still unclear whether these changes are actually affecting teens’ health, though—or even if fluoride is really the main culprit.

In the 1950s and 1960s, states and cities in the U.S. began adding fluoride to drinking water supplies, following decades of research and anecdotal reports showing that fluoride could prevent tooth decay, especially in children. Today, close to two-thirds of the country drinks fluoridated water, while other countries have adopted similar policies. And water fluoridation continues to be endorsed by public health and dental organizations as one of the most worthwhile and cost-effective health policies ever implemented (in the U.S., fluoridation is thought to cost an average dollar per person, far less than the medical costs of treating even one cavity).

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There’s long been a small contingent of fluoride skeptics, though. Their claims have largely hinged on (lampooned) accusations of government overreach and communist indoctrination. But some scientists have also argued that fluoridation as it exists today could have unintended, harmful health effects.

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We know, for instance, that very high levels of fluoride (higher than you’d ever find in fluoridated tap water) can cause neurological problems in adults. Some research has also linked low levels of fluoride exposure to cognitive problems in developing young animals, while a few population studies in people have found a connection between fluoride exposure and lower IQ in children. But these studies have largely focused on people living in China, where fluoride is naturally found in groundwater in sometimes very high levels.

The authors of this current study, published in Environment International, instead looked at more than 3,000 teens in the U.S. They used data from a nationally representative and government-run annual survey of Americans, including some people who also gave blood samples. With these samples, the team was able to track levels of fluoride, as well as markers of kidney and liver health, in the blood of these teens. They focused on the kidney and liver because these two organs are the most exposed to fluoride when it’s absorbed by the body. And any possible effects might be amplified in teens, since they’re less able than adults to quickly filter out fluoride through their urine.

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“What we found, in a nutshell, is that higher levels of fluoride in blood were associated with indicators of poor kidney and liver function,” lead author Ashley J. Malin, a postdoctoral fellow in the Department of Environmental Medicine and Public Health at the Icahn School of Medicine at Mount Sinai, told Gizmodo by phone.

The study’s findings suggest that current levels of fluoride exposure in the U.S. can lead to reductions in kidney and liver function in at least some teens. And while the teens seemed to be healthy now, even small reductions in kidney function could increase their risk for kidney disease later in life. At the same time, Malin added, it’s too early to say anything conclusive.

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“So, at this point, we don’t fully know what the clinical implications are of these small changes,” she said. “We really need more research to fully understand these implications.”

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An ideal study in the future, Malin said, would look at and compare similar groups of young people exposed to varying levels of fluoridated water from a very early age and track their health over time.

One question that more research could answer is the exact direction of the fluoride link. Maybe it’s not that chronic low-level fluoride exposure leads to poorer kidney function, but that people with preexisting poor kidney function are less able to metabolize fluoride, so more of it ends up in their blood. That could still be bad, since the more fluoride accumulates in our bodies, the greater the potential health risks, but it would be a different problem to solve.

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Malin and her team aren’t saying their findings should lead to changes in fluoridation policy. But she does think it’s important for public health experts to look more into these possible connections and, if needed, to reevaluate the consensus around fluoridation.

A reevaluation of fluoride policies wouldn’t be a first for the U.S. government in recent years. In 2015, the Department of Health and Human Services recommended that the optimum level of fluoride in drinking water should be 0.7 milligrams per liter of water, rather than the range of 0.7 milligrams to 1.2 milligrams previously endorsed. At that level, the agency concluded, you would still prevent cavities while lowering the risk of dental fluorosis, a condition that causes developing teeth to become brown, stained, or even damaged in children overexposed to fluoride.

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“I think that policymakers should continue to consider the research that is coming out, so they can make the best decision for everyone possible. And I hope my research helps them with that,” she said.

Of course, preventing tooth decay is about much more than cosmetics—poor oral health is linked to a range of problems throughout the body, including heart disease, arthritis, and even dementia. So until there’s compelling evidence that fluoride in drinking water causes harm, the weight of the evidence falls on it being a boon for public health.

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