Or, that if you can survive the thing that kills the rest of their cohort, it has beneficial tradeoffs. As in, perhaps smoking protects from Alzheimer's, if it doesn't kill you first.
replyControlling for age in a profession with a high fatality rate like this seems like controlling for high alertness, consciousness, quick reaction times, and well restedness/low stress, low recreational drug and alcohol use.
replyOf those, sleep issues are highly correlated with Alzheimer's and also with auto accidents. Controlling for age alone here would select for low incidence of sleep issues.