# Intelligence and neuroticism in relation to depression and psychological distress: evidence of interaction using data from Generation Scotland: Scottish Family Health Study and UK Biobank

## TL;DR

Higher intelligence may reduce the negative effects of neuroticism on depression and psychological distress, based on data from two large studies.

## Contribution

This study provides evidence that general intelligence interacts with neuroticism to mitigate risks for depression and distress.

## Key findings

- Higher intelligence reduces the adverse effects of neuroticism on major depressive disorder in UK Biobank.
- Intelligence protects against the negative impact of neuroticism on psychological distress in both cohorts.
- Neuroticism is consistently associated with increased risk of depression and distress across both studies.

## Abstract

Neuroticism is a risk factor for selected mental and physical illnesses and is inversely associated with intelligence. Intelligence appears to interact with neuroticism and mitigate its detrimental effects on physical health and mortality. However, the inter-ralationships of neuroticism and intelligence for major depressive disorder (MDD) and psychological distress has not been well examined.

Associations and interactions between neuroticism and general intelligence (g) on MDD and psychological distress were examined in two population-based cohorts: Generation Scotland: Scottish Family Health Study (GS:SFHS, N=19,200) and UK Biobank (N=90,529). The Eysenck Personality Scale Short Form-Revised measured neuroticism and g was extracted from multiple cognitive ability tests in each cohort. Family structure was adjusted for in GS:SFHS.

Neuroticism was associated with MDD and psychological distress in both samples. A significant interaction between neuroticism and g in predicting MDD status was found in UK Biobank (OR = 0.96, p < .01), suggesting that higher g ameliorated the adverse effects of neuroticism on the likelihood of having MDD. This interaction was not found in GS:SFHS. In both samples, higher neuroticism and lower intelligence were associated with increased psychological distress. A significant interaction was also found in both cohorts (GS:SFHS: ß = -0.05, p < .01; UK Biobank: ß = -0.02, p < .01), such that intelligence protected against the deleterious effect of neuroticism on psychological distress.

From two large cohort studies, our findings suggest intelligence acts a protective factor in mitigating the effects of neuroticism on risk for depressive illness and psychological distress.