Reaction times match IQ for major causes of mortality: evidence from a population based prospective cohort study

Introduction: The association of premorbid cognitive ability with all-cause mortality is now well established. However, since all-cause mortality is relatively uninformative about aetiology, evidence has been sought, and is beginning to accumulate, for associations with specific causes of mortality. Likewise, the underlying causal pathways may be illuminated by considering associations with different measures of cognitive ability. For example, critics of IQ type measures point to possible cultural or social biases and there is, consequently, a need for more culturally neutral measures such as reaction times. We examine the associations of cognitive ability with major causes of mortality, including: cardiovascular disease, cancer and respiratory disease and compare the results for a standard IQ test, the Alice Heim 4 (AH4), with those for simple and four-choice reaction times. Methods: Data were derived from the oldest cohort of the West of Scotland Twenty-07 Study. Participants were randomly sampled from the Central Clydeside Conurbation, a mainly urban area centred on Glasgow city. At baseline, aged 56, they were interviewed in their homes by trained interviewers; the AH4 was administered and reaction times measured using a portable electronic device. Vital status was ascertained via linkage to the NHS central register. Cox regression was used in SAS 9.4 for the main analyses. Adjustments were made for sex, smoking status and social class. Results: Full data on AH4, RT and covariates were available for 1350 out of 1551. During 29 years of follow-up, there were 833 deaths: 279 cardiovascular disease (CVD) (168 CHD; 68 stroke); 291 cancer; 97 respiratory disease; 42 digestive disease; and 39 dementia. The 85 remaining deaths were a heterogeneous mixture with no cause accounting for more than 14. AH4 scores were associated with most major causes. Digestive disease and dementia had similar effect sizes but were not significant. Within cardiovascular disease, there was an association with coronary heart disease but not stroke. The association with cancer was primarily due to those cancers related to smoking. RT measures were mostly associated with the same causes of death. Where significant, effects were in the same directions and of similar magnitude. That is, lower AH4 scores, longer reaction times, and more variable reaction times were all associated with increased mortality risk from the major causes of death. A summary measure of RT outperformed the AH4 for most causes. Conclusion: The association between intelligence with mortality from the major causes is also seen with reaction times. That effect sizes are of similar magnitude is suggestive of a common cause. It also implies that the association of cognitive ability with mortality is unlikely to be due to any social, cultural or educational biases that are sometimes ascribed to intelligence measures