Lithium - the lightest of all solid elements - doesn't just power rechargeable batteries. Traces of lithium permeate virtually every rock on our planet, and are found in our food and water supply. According to a new analysis, this invisible presence could have a measurable effect on our lives.
For decades, lithium has been an often life-saving medication for people with mood disorders, most notably bipolar, with a proven ability to stabilise moods and reduce the risk of suicide in these highly vulnerable patients.
The doses used in psychiatry are relatively high - at least 200 milligrams per day, and side-effects have to be carefully monitored. But some research has indicated that even microdoses of the element, just 400 micrograms daily, can produce an improvement in mood (there are 1,000 micrograms in a milligram).
Since the 1990s, scientists have wondered whether the naturally occurring lithium in drinking water supplies across the world could produce effects at the level of the entire population - lower suicide rates, decreased violence, even less dementia.
Over the years, a slew of observational or ecological studies have hinted at an association between higher levels of lithium in the public water supply, and lower rates of suicide mortality in the local population.
Now, a team of researchers in the UK has produced the first-ever meta-analysis of such studies, confirming this link. We don't know why this might be the case, but it's a curious path to tread.
"It is promising that higher levels of trace lithium in drinking water may exert an anti-suicidal effect and have the potential to improve community mental health," says lead author of the review, epidemiologist Anjum Memon from Brighton and Sussex Medical School.
The team thoroughly searched the literature, ending up with 15 studies they used in a qualitative synthesis, narrowed down further for a meta-analysis of nine studies.
In total, their analysis comprised data from 1,286 localities across Japan, Austria, the US, England, Greece, Italy, and Lithuania. The mean lithium levels found in the drinking water samples ranged from just 3.8 micrograms per litre (μg/L) to 46.3 μg/L, with a few communities peaking above 80 μg/L.
An extensive crunch of the numbers revealed that higher lithium levels naturally occurring in drinking water were indeed linked with lower levels of suicide mortality in the area - what's known as an inverse association.
Of course, as with any complex analysis of the available literature, the results come with important caveats. The team emphasises that ecological studies are conducted to generate hypotheses - rather than being an answer, they're basically just posing the question.
"They are subject to confounding as information on potential confounder(s) may not be available and associations at the population level do not necessarily represent associations at the individual level (ecological fallacy)", they write.
Details on social classes, the prevalence of mental disorders in a population, and even how much people move around can all affect the observational results, not to even mention the fact we also get lithium from our food - and that impact has not been investigated.
"Furthermore, bottled drinking water (processed/treated or natural mineral water from springs) often has a much higher lithium content than tap water – the association between exposure to lithium via bottled water and suicide has not been studied," the team notes.
In light of their findings, the researchers do recommend randomised community trials of supplementing the water supply with lithium, as "a possible means of testing the hypothesis", along with research into food sources of lithium.
Scientists are still working to paint the full picture of how lithium even works, why it can have such a beneficial effect on one's mood levels, and whether the anti-suicidal effects of the element are entirely separate.
Of course, to some this will inevitably sound as the beginnings of a government conspiracy. But there are plenty of experts willing to urge caution before we start any supplementation trials, and plenty of data left to gather.
And if we don't ask the questions, we can't expect an answer.
The review was published in The British Journal of Psychiatry.
If this story has raised concerns or you need to talk to someone, here's a list where you may be able to find a crisis hotline in your country.