We must discover why cognitive differences are related to morbidity and mortality, argues Ian Deary, of the University of Edinburgh Centre for Cognitive Ageing and Cognitive Epidemiology, in an Essay in Nature (456, 175-176; 2008), in order to help tackle health inequalities.
“Intelligence can predict mortality more strongly than body mass index, total cholesterol, blood pressure or blood glucose, and at a similar level to smoking”, he writes. “But the reasons for this are still mysterious. That needs to change. Reducing health inequalities is a priority, and to do that we need to determine their causes.”
The Essay discusses the four main, non-exclusive explanations for this phenomenon: first, that intelligence is associated with more education, and hence subsequently with professions that tend to place the person in healthier environments; second, that more intelligent people have healthier lifestyles; third, early-life “insults” have some role; and fourth, mental-test scores taken in youth might relate to a “well-put-together system”.
What are the psychological characteristics associated with living longer? Why do we die when we do, and to what extent is this question tractable? According to Prof. Deary, “the influence of intelligence on mortality isn’t fated; intelligence does not unalterably spin, measure and cut the thread of life. The things that people with higher intelligence have and do that make them live longer may be found and, we hope, shared, towards the goal of better and more equal health.”