Here’s a claim I hadn’t heard before but seems to be fairly well established: lead poisoning increases rates of violent crime and when you take lead out of gasoline, violent crime drops. Here’s Yglesias:
When I read the New York Times writing about a 40 percent fall in Jamaica’s murder rate (it’s still very high) I naturally wondered about Kevin Drum’s lead angle. And he says it fits the pattern: From 1990 to 2000, Jamaica started phasing out leaded gasoline. From 2009 to 2013, the crime rate has fallen forty percent. In other words, Jamaica is likely starting to see the beneficial impact of a youth cohort with lower levels of lead poisoning. And just based on the lead channel alone you’d expect to see meaningful further improvements over the next 5-10 years as the kids who were born after the complete eradication of leaded gasoline grow up.