BACKGROUND: In the last decade, an increasing body of empirical evidence has gathered to establish an association between higher cognitive ability in youth and later mortality, less morbidity and better health. This field of research is known as cognitive epidemiology. The causes of these associations are not understood. OBJECTIVE: Among the possible explanations for the associations is the suggestion that they might, in part, be accounted for by general bodily 'system integrity'. That is, scoring well on cognitive ability tests might be an indicator of a more general tendency for complex systems in the body to be efficient. The construct of system integrity is critically assessed. METHOD: This viewpoint provides a critical presentation and an empirical and theoretical evaluation of the construct of system integrity as it is used in cognitive epidemiology. RESULTS: A precedent of the system integrity suggestion is discovered. The empirical tests of the system integrity idea to date are critically evaluated. Other possible routes to testing system integrity are suggested. There is a critical re-evaluation of the idea and other, related concepts. CONCLUSION: The construct of system integrity is distinct from related constructs. It is still underdeveloped theoretically, and undertested empirically within cognitive epidemiology.
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