The same can be said of lead. I'm fairly certain I've read of a study / theory that the drop in crime rates can be tracked back to removing lead from paint, gasoline, etc.

Full disclosure: I don't recall if this jumped the gap between correlation and cause.

I think that explanation is pretty widely accepted as being a cause of the past few decades' drop in crime rates (though not the only one). It's probably not possible to prove cause better than we have without obviously unethical experimental studies.

Obviously unethical government policies might suffice: Flint, MI.

As a side note, n=1 thing, over the counter lithium orotate is great for me as a mild anxiolytic when work related stress kicks in.