Consistent and replicable findings were found suggesting higher neuroticism associates with increased psychological distress, whereas higher intelligence associates with reduced psychological distress. A small interaction was found across samples such that lower distress associates with higher intelligence and lower neuroticism. Although these results are of small magnitude, they suggest an important interaction whereby higher g lessens the strength of the neuroticism-distress association.
This is the first study of intelligence’s potential protective influence on MDD [63], self-reported depression, and psychological distress in high neuroticism individuals. Consistent with previous research the strong link between neuroticism with increased risk for depression and psychological distress was replicated with moderate effect sizes. Although longitudinal work suggests intelligence provides protection to mental health[24,28,29], we found g increased the risk for depression when adjusted for neuroticism. The magnitude of this risk was very small, however. Across cohorts, intelligence associated with decreased levels of psychological distress. A modest association of intelligence as a mitigating factor in reducing psychological distress in individuals with high neuroticism was found in both cohorts. Although this study suggests intelligence provides a protective function in self-reported depression and psychological distress (which mirrors previous research [23,41,42]), intelligence was not found to be protective against diagnosis of depression in those high in neuroticism.
It is unclear why intelligence associates with protection to risk for psychological distress, but not MDD. One supposition is that individuals with higher intelligence may be more likely to seek help, and therefore are more likely to receive a clinical diagnosis of depression. Another postulation could be that intelligence has an effect only during times of depressive episode. A state-dependent association of cognitive ability has been suggested in which variability in intelligence co-varies with depressive episode and remission (for a comprehensive review, see Sackeim and Steif [26]). As such, subsequent investigations may benefit from addressing the same hypotheses examining individuals with current MDD in comparison to individuals in remission, and controls. Increased psychological distress is an established symptom of depression and often used in clinical diagnosis [31,32]. Goldberg [33] described distress as representing the overall severity of depression and so it is likely that individuals scoring highly on measures of psychological distress may be more likely to self-report the disorder, irrespective of its clinical significance. However, we must be mindful of the complexities
of causality; whilst it is likely that the neuroticism trait prospectively predicts later distress and self-reported depression, we cannot be certain that these factors are not manifestations of the same underlying risk.
Intelligence could be a marker of system integrity [64] in which increased intelligence circumvents negative mood biasing in individuals high in neuroticism that may lead to distress and disorder [65]. Alternatively, more intelligent individuals may be better able to employ successful coping mechanisms during times of distress: higher intelligence associates with increased resilience to adversity in children [66]. Research suggests that psychosocial factors are associated with resilience to mood disorders [67]. Proactive and psychosocial coping mechanisms may enable individuals decrease transient feelings of distress and to implement established, effective strategies learned from previous exposure to distress or depression [68]. This possibility is consistent with the finding that whereas g and neuroticism interacted to associate with reduced psychological distress, the same interaction was not found in clinical MDD. It would be interesting to explore intelligence’s influences on coping style [69] and subsequent psychological distress and MDD diagnosis in future investigations. Intelligence may influence the adoption of specific coping strategies, and this could be a mediating factor in the ‘depressogenic’ process.
