Many believe that humanity’s caffeine addiction has wrought a lot of benefits. Earlier in the week, historian Mark Pendergrast told us about how coffee (and caffeine) helped Western civilization “sober up” enough to get down to business. And Jerry Seinfeld claimed coffee has made us a more productive society.

But is there any science behind the idea that caffeine, by way of coffee, makes us better workers? And what exactly is caffeine doing to our tired brains?

Of course, there’s a huge amount of variation in how caffeine affects individuals, which depends on genetics, tolerance and other factors. But several small studies have shown that at low doses (between 100 and 250 mg), caffeine improves alertness and mental performance, especially in people who are already tired. Neuroscientists report that it makes us more supportive of each other in social situations. And one study even found that higher caffeine consumption helped reduce the risk of workplace accidents.

As with all drugs, there is such a thing as too much caffeine. According to a 2001 Institute of Medicine report, 600 mg of caffeine (or six cups of coffee) will bring on negative cognitive effects, otherwise known as the jitters, in most people — including Kramer from Seinfeld. And some people are so sensitive to caffeine that one cup will bring on nervousness and irritability, rather than the alertness that most of us feel.