***Article first published by 'Vox' on Oct. 24, 2018***

Lithium is a potent psychiatric drug, one of the primary prescribed medications for bipolar disorder. But it’s also an element that occurs naturally all over the Earth’s crust — including in bodies of water. That means that small quantities of lithium wind up in the tap water you consume every day. Just how much is in the water varies quite a bit from place to place.

Naturally, that made researchers curious: Are places with more lithium in the water healthier, mentally? Do places with more lithium have less depression or bipolar or — most importantly of all — fewer suicides?

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.

Ghaemi and a number of other eminent psychiatrists are making a pretty remarkable claim. They think we could save tens of thousands of lives a year with a very simple, low-cost intervention: putting small amounts of lithium, amounts likely too small to have significant side effects, into our drinking water, the way we put fluoride in to protect our teeth.

The case for skepticism on lithium

The size of the numbers Ghaemi is claiming should make you skeptical: Those are huge, arguably implausibly huge, effects. In 2015, the Open Philanthropy Project, a large-scale grantmaking group in San Francisco, shared an analysis with me implying that if two specific studies were right, a “small increase in the amount of trace lithium in drinking water in the U.S. could prevent > 4,000 suicides per year.” That’s significant, but far short of 15,000 to 25,000.

And while Ghaemi is very enthusiastic about the potential of groundwater lithium, other researchers are more wary. A comprehensive list of lithium studies, updated just last month, shows that while many studies find positive effects, plenty more found no impact on suicide or other important outcomes. In particular, a large-scale Danish study released in 2017 found “no significant indication of an association between increasing … lithium exposure level and decreasing suicide rate.”

The Open Philanthropy Project, which had previously been quite interested in new research on lithium, states on its website that the study “makes us substantially less optimistic” that trace lithium really helps guard against suicides.

Just this year, a study using health care claims data in the US found that greater amounts of trace lithium in the water didn’t predict lower diagnoses of bipolar disorder or dementia. That’s a different outcome than suicides, but also suggests that low doses of lithium might not have a profound effect.

Why this hasn’t been tried

These recent studies have made me less confident in the link between lithium and lower suicide rates than I was when I first encountered Ghaemi’s research. But it’s such a cheap intervention, and the odds of serious side effects sound low enough, that it seems worth a try.

At the very least, I’d love for some governments to conduct real, bona fide experiments on lithium. Maybe a state could randomly add lithium to some of its reservoirs but not others, or, conversely, a high-lithium state could try removing it from the water. There are serious ethical questions about doing experiments like this that affect whole populations, but if lithium’s effect is real and we don’t pursue it because we lack compelling enough evidence, thereby endangering thousands of people — that’s an ethical problem too.

But no study like that has been conducted. And if you want to know why, you should consider the case of fluoride.

As you probably know, putting fluoride in our drinking water dramatically reduced tooth decay, by around 25 percent per the Centers for Disease Control and Prevention. But as you likely also know, the initial rollout of fluoride in the 1940s and 1950s was intensely controversial.

Jesse Hicks, a science journalist who wrote a great history of the fluoride wars, told me on this week’s Future Perfect podcast that the backlash started in Stevens Point, Wisconsin, with a local gadfly named Alexander Y. Wallace who was convinced the substance was poison, and who wrote a parody song called “Goodnight, Flourine” to the tune of the folk song “Goodnight, Irene.”

From there, the conspiratorial, far-right John Birch Society became convinced that fluoride was a Communist plot; the Ku Klux Klan came out against fluoride too. “I think part of the longevity of this controversy has to do with the way it can activate so many different biases and prejudices,” Hicks told me. “As soon as you start talking about putting something in the water supply you have small or anti-government people responding very vigorously against that.”

The absurd controversy continues to this day. Dr. Mehmet Oz, the wildly popular, wildly irresponsible TV doctor, has brought on a fluoride conspiracist — Erin Brockovich of Julia Roberts movie fame — to sow fear and disinformation.

If that’s the reaction to an effort to improve dental health, just imagine the public outcry against a major push for adding lithium to the water. The rap against fluoride, mocked in movies like Dr. Strangelove, is that it’s a mind-control plot. But putting lithium in the water would actually be a mind-control plot: It would be a concerted effort by the government to put mind-altering chemicals in the water supply to change the behavior of the citizenry. And I say that as someone who thinks that, if it works, that it would be a great idea! Preventing suicide is really important, but it does require changing how people think, a tiny bit.

So figuring out if, and how well, trace lithium in the water works is only half the battle. Advocates would then have to win over a very, very skeptical public.

Hicks thinks we need a rock-solid, impenetrable scientific case if we’re going to do it. The science so far is promising, but not firm enough. “When you start making it a public health policy, you activate all of these other considerations that make it that much harder to make it happen,” he says.

For more, listen to the full episode above, and be sure to tune in again next Wednesday for more Future Perfect!

Read more:

Anna Fels’s op-ed “Should We All Take a Bit of Lithium?” in the New York Times
Nassir Ghaemi and colleagues review the evidence on trace lithium and suicide, homicide, crime, and dementia
The recent Danish study casting doubt on the trace lithium/suicide prevention link
Jesse Hicks explains the fluoride controversy for the Science History Institute
Jesse Hicks explains trace lithium, for Vice
More of Vox’s effective altruism coverage