Why do smart people live longer?

Numerous research studies have correlated higher IQs with longer lifespans. Why? One reason could be that smarter people apparently don't do as many dumb things that could kill them early. In Scientific American, Michigan State University psychologist David Z. Hambrick looks at the latest research in cognitive epidemiology:

One possibility is that a higher IQ contributes to optimal health behaviors, such as exercising, wearing a seatbelt, and not smoking. Consistent with this hypothesis, in the Scottish data, there was no relationship between IQ and smoking behavior in the 1930s and 1940s, when the health risks of smoking were unknown, but after that, people with higher IQs were more likely to quit smoking. Alternatively, it could be that some of the same genetic factors contribute to variation in both IQ and in the propensity to engage in these sorts of behaviors.

Another possibility is that IQ is an index of bodily integrity, and particularly the efficiency of the nervous system.

"Research Confirms a Link between Intelligence and Life Expectancy"