Background The association of premorbid cognitive ability with all-cause mortality is well established. Less is known about specific causes. All-cause mortality is relatively uninformative about aetiology and more evidence is needed for specific causes, particularly the major causes of death. Critics of IQ point to possible cultural biases and the need for neutral measures, like reaction times. We examine the association of cognitive ability with major causes of mortality, including: CHD, cancer and respiratory disease. The measures of cognitive ability include a standard IQ test, the Alice Heim 4 (AH4), as well as four-choice reaction times (RT).
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 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, Social Class and baseline self-rated health.
Results Full data on AH4, RT and covariates were available for 1305 out of 1551. During 26 years of follow-up, there were 707 deaths: 148 CHD; 53 stroke; 262 cancer; 84 respiratory; and 160 ‘other’ causes. AH4 scores and reaction times showed strong and robust associations with mortality from CHD, respiratory disease and other causes. There was little evidence for an association with stroke but some for cancer; subsequent analysis showed this to be due to lung cancer deaths. Hazard ratios were only partially attenuated when adjusted for smoking status, social class and self-rated health. Adjusted hazard ratios (95% CIs) for AH4 and RT mean were: for CHD 1.25 (1.02, 1.54) and 1.29 (1.09, 1.52), respectively; for respiratory disease 1.36 (1.03, 1.78) and 1.37 (1.12, 1.68); and for other causes 1.40 (1.15, 1.70) and 1.41 (1.22, 1.63).
Conclusion These results confirm earlier analyses of all-cause mortality carried out after 14 years of follow-up. CHD and respiratory diseases are identified as two likely components of the relationship. Association with the residual category of ‘other’ causes suggests more components yet to be discovered. The similar results for reaction times imply that social or cultural biases do not explain the association between cognitive ability and mortality.
- Cognitive epidemiology
- reaction times
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