A new study suggests a link between high levels of fluoride and lowered IQ. It's heating up arguments over fluoridating drinking water, which dentists say is critical for protecting teeth.

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Fluoridating the public water supply has been common practice for nearly 80 years in the U.S. It's an acclaimed public health intervention that helps prevent cavities. For just as long, some have raised concerns about the practice that can veer from evidence-based to unsubstantiated conspiracy. An analysis by government researchers, published Monday in JAMA Pediatrics, is adding to the debate. The research found that exposing babies and kids to high levels of fluoride might be associated with neurodevelopmental harm. Frankly, it's a lot to digest — so we invited health correspondent Pien Huang onto the show to wade through the debate.

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2024 was full of science news. There was a total solar eclipse, the Paris Olympics, elections in the United States and elsewhere, technological breakthroughs and many space launches. But perhaps above all, it was a huge year in health. So, today, we're talking through some of 2024's biggest health stories — from what's in our drinking water supply, to bird flu, obesity drugs and this year's record heat. They're also the stories we think will continue to be big in 2025. See you in the new year, Short Wavers! <3

Questions or suggestions for what else we should cover? Email us at shortwave@npr.org!

Listen to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ at plus.npr.org/shortwave.

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Water utilities across the country will have to comply with EPA limits on "forever chemicals" in drinking water by 2029. Orange County, Calif., got a head start.

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Chemical companies and water utilities are challenging the EPA’s recent rule putting limits on six PFAS chemicals in drinking water.

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Wednesday the Environmental Protection Agency announced new drinking water standards to limit people's exposure to some PFAS chemicals. For decades, PFAS have been used to waterproof and stain-proof a variety of consumer products. These "forever chemicals" in a host of products — everything from raincoats and the Teflon of nonstick pans to makeup to furniture and firefighting foam. Because PFAS take a very long time to break down, they can accumulate in humans and the environment. Now, a growing body of research is linking them to human health problems like serious illness, some cancers, lower fertility and liver damage. Science correspondent Pien Huang joins the show today to talk through this new EPA rule — what the threshold for safe levels of PFAS in tap water is, why the rule is happening now and how the federal standards will be implemented.

Read more of Pien's reporting on the EPA's first ever rule on PFAS in drinking water.

Want to hear more about health and human safety? Email us at shortwave@npr.org — we might cover your question on a future episode!

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A new government study estimates that at least 45% of the nation's tap water could be contaminated with one or more forms of PFAS. Here's what to do if you're worried about what's in your faucet.