A 2014 review of studies concluded that the answer was yes: Four of five studies reviewed found that places with higher levels of trace lithium had lower suicide rates. And Nassir Ghaemi, the Tufts psychiatry professor who co-authored that review, argues that the effects are large. High-lithium areas, he says, have suicide rates 50 to 60 percent lower than those of low-lithium areas.

“In general, in the United States, lithium levels are much higher in the Northeast and East Coast and very low in the Mountain West,” he told me on a new episode of the Vox podcast Future Perfect. “And suicide rates track that exactly — much lower suicide rates in the Northeast, and the highest rates of suicide are in the Mountain West.”

If you apply that 50 to 60 percent reduction to the US, where about 45,000 people total died by suicide in 2016, you get a total number of lives saved at around 22,500 to 27,000 a year. That’s likely too high, since you can’t reduce suicide rates in places that are already high-lithium. Ghaemi’s own back-of-the-envelope calculation is that we’d save 15,000 to 25,000.