Genetic contribution to the relationship betweenpersonality and depressive symptoms among olderwomenI. Pakkala1*, S. Read2, J. Kaprio3,4, M. Koskenvuo3, M. Kauppinen1and T. Rantanen11Finnish Centre for Interdisciplinary Gerontology, University of Jyva¨skyla¨, Finland2London School of Hygiene and Tropical Medicine, UK3Department of Public Health, University of Helsinki, Finland4Department of Mental Health and Alcohol Research, National Public Health Institute, FinlandBackground. Prior studies suggest that certain types of personality are at higher risk for developing depressivedisorders. This study examined the relationship between old age depressive symptoms and two middle-agepersonality dimensions, neuroticism and extraversion.Method. The present study is part of the Finnish Twin Study on Aging, where altogether 409 female twins whohad completed the Eysenck Personality Inventory at the age of 38–51 years were studied for depressive symptoms28 years later using Center for the Epidemiologic Studies Depression Scale. Logistic regression analysis suitable fordependent data and univariate and Cholesky models for decomposing the genetic and environmental factor wereused.Results. Middle age extraversion protected from later depressive symptoms while neuroticism increased the risk.Twin modeling indicated that the association between neuroticism and depressive symptoms resulted from sharedgenetic risk factors common to both traits. However, a substantial proportion of the genetic vulnerability was specificto old age depressive symptoms and was not shared with neuroticism. Middle age extraversion had no geneticrelationship with old age depressive symptoms.Conclusions. The relationship between middle age neuroticism and old age depressive symptoms is strong but onlypartly the result of genetic factors that predispose to both neuroticism and depressive symptoms. Extraversion, bycontrast, has no genetic relationship with depressive symptoms experienced in old age.Received 12 January 2009 ; Revised 6 August 2009 ; Accepted 17 August 2009 ; First published online 8 October 2009Key words : Aging, depressive symptoms, personality, twins.IntroductionThere is accumulating evidence that certain types ofpersonality are at higher risk for developing depress-ive disorders (e.g. Kendler et al. 1993; Fanous et al.2002). Several studies have suggested that the per-sonality trait most closely related to depressive dis-order is neuroticism (Roberts & Kendler, 1999;Kendler et al. 2006a; Steunenberg et al. 2006). Neuro-ticism and depression have been associated in clinical(Duberstein & Heisel, 2007), family (Duggan et al.1995), twin (Kendler et al. 2006a; Fanous et al. 2007)and general population-based (Romanov et al. 2003 ;Jylha¨& Isometsa¨, 2006) studies. Earlier twin studies(e.g. Kendler et al. 2006a) have also found a geneticcorrelation between these two traits, which indicatesthat genes having an impact on neuroticism are alsolikely to affect depression. The association betweenextraversion and depression has instead been contro-versial as some studies have found that extraversionprotects from later depressive symptoms (Jylha¨&Isometsa¨, 2006), while other studies have found noassociations (Kendler et al. 1993). Also, twin studiesinvestigating a genetic correlation between extraver-sion and depression have found contradictory results,where some studies have detected a modest geneticcorrelation between these traits (Kendler et al. 2006a),whereas others have not (Kendler et al. 1993).The mean levels and test–retest correlations of per-sonality traits are mostly consistent in adulthood andold age (Caspi et al. 2005). Extraversion and neuroti-cism are also moderately heritable and the greatestsources of individual differences during adulthood are* Address for correspondence : I. Pakkala, M.Sc., Finnish Centre forInterdisciplinary Gerontology, University of Jyva¨skyla¨, P.O. Box 35(Viveca), FIN-40014 University of Jyva¨skyla¨, Finland.(Email : [email protected].fi)Psychological Medicine (2010), 40, 1357–1366. f Cambridge University Press 2009doi:10.1017/S0033291709991401ORIGINAL ARTICLEnon-shared environmental influences (for a review,see Bouchard & Loehlin, 2001). The genetic and en-vironmental influences on personality are relativelystable over time in adulthood and old age (Viken et al.1994; Pedersen & Reynolds, 1998 ; Johnson et al. 2005 ;Read et al. 2006). Depressive symptoms are also ge-netically influenced, although several studies havegenerally shown rather low genetic effects and con-siderable unique environmental effects explainingindividual differences in adulthood and old age (Gatzet al. 1992; Carmelli et al. 2000 ; Jansson et al. 2004).The relationship between depression and person-ality is complex. Personality characteristics may pre-dispose to, result from or modify the expression ofdepressive illness (Kendler et al. 1993). A powerfulnatural experiment with which to evaluate such riskfactors would include both longitudinal and geneticdesigns. We report here the results of a study wherewe have followed initially middle-aged female twinpairs for 28 years and assessed their personalityat baseline and depressive symptoms at follow-up.Among older adults, depressive symptoms not meet-ing the diagnostic criteria for depression are highlyprevalent, while their consequences for disability riskand decrease in well-being are similar to those ofclinical depression (Blazer, 2003). Understanding whatcharacteristics of personality increase the risk for de-pression in old age could provide a window to theetiology of depression and therefore provide a morerational basis for targeted preventive interventions.Investigating early personality factors would also offeropportunities for identifying those younger personswho are at risk for developing depressive symptomslater in life. Studying depressive symptoms amongolder women is also well-grounded as depressivesymptoms in later life are more prevalent amongwomen than men (Piccinelli & Wilkinson, 2000).Our objective in the present study was to investigateif middle age personality traits of neuroticism andextraversion are associated with depressive symptomsexperienced in old age. Using quantitative trait mod-eling, we also wanted to investigate to what extentthe correlation between neuroticism, extraversion anddepressive symptoms is due to shared genetic and/orshared environmental factors.MethodSubjectsThe present study is a part of