In 2001 researchers in Great Britain were surprised to discover that people with low IQs live shorter lives. But a more startling finding came this year with a report that reaction time proved an even stronger predictor of life span than IQ.

Ian Deary, a psychologist at the University of Edinburgh, and Geoff Der, a statistician at the MRC Social and Public Health Sciences Unit in Glasgow, suspected that higher IQ might lead to healthier habits like not smoking or healthier environments like safer office jobs. So they looked at data on 898 people first tested at about age 56, and then tracked their survival until age 70. They found that the link between IQ and mortality held strong even after adjusting for education, occupation, social class, and smoking.

But the group had also taken button-pressing reaction-time tests, which measure how quickly and accurately a person repeatedly makes a simple decision. Deary and Der wanted to find out whether there was still a relationship between mental ability and survival once a person’s reaction time was taken into account. “And there wasn’t,” Deary says. The upshot: “We could explain the association between mental ability and survival with reaction time.” In this study, the reaction times tested in subjects at age 56 appeared to have about as strong a link to chances of survival over the next 14 years as did being a smoker.

Why is still uncertain. One possibility is that reaction time slows because an undetected disease has begun to compromise performance. Another hypothesis is that the differences result from more fundamental, lifelong variations in the speed at which people process information. Both factors could be at work. For clues, Deary hopes to track a younger sample over several years.

The study has sparked interest in what its authors call “cognitive epidemiology,” the study of associations between mental ability tests and health outcomes. “One of the indicators of whether mental ability tests are useful is whether they predict things about real life,” Deary says, and these findings suggests they do.

COPYRIGHT 2006 © Marina Krakovsky. All Rights Reserved.