Does cognition predict mortality in midlife? Results from the Whitehall II cohort study

The authors examined the association of 'g' (general intelligence) factor and five specific cognitive measures assessed in 1997-1999 with mortality till 2006 (mean follow-up of 8 years) in the middle-aged Whitehall II cohort study. In age- and sex-adjusted analysis, a decrease in 1 S.D. in memory (hazard ratio (HR), 1.19; 95% confidence interval (CI): 1.02, 1.39) and in Alice Heim 4-I (AH4-I) (HR, 1.16; 95% CI: 1.01, 1.35) was found to be associated with higher mortality. The association with 'g' factor, phonemic and semantic fluency did not reach significance at p<0.05. No association was found with vocabulary. Out of education, health behaviours and health measures, it was health behaviours that explained the greater part of the association between cognition and mortality, ranging from 21% for memory to 70% for semantic fluency. All the covariates taken together explained only 26% of the association with memory and between 33 and 90% for the other cognitive measures. This study suggests that 'g' type composite measure of cognition might not be enough to understand the associations between cognition and health.