title: The impact of environmental experiences on symptoms of anxiety and depression across the life span.
abstract: Symptoms of anxiety and depression are relatively stable over time. Can this stability be explained by genetic influences, or is it caused by the long-lasting effects of accumulating environmental experiences? To address this question, we analyzed longitudinally assessed symptoms of anxiety and depression in eight samples of monozygotic twins of widely varying ages. These samples were drawn from American and European population-based registries. Using hierarchical linear modeling, we examined individual differences and individual changes in the level of symptoms over time. This method enabled us to decompose the variance into the predictable variance shared by both members of each pair of twins, the differences between individuals within pairs, and the residual variance. We then modeled how these components of individual variation changed over time. Within pairs, the twins' predicted levels of symptoms increasingly diverged from childhood until late adulthood, at which point the divergence ceased. By middle adulthood, environmental experiences contributed substantially to stable and predictable interindividual differences in levels of anxiety and depression.
authors.affiliation: Department of Psychiatry, Virginia Institute for Psychiatric and Behavioral Genetics, Virginia Commonwealth University, Richmond, VA 23298, USA. kendler@vcu.edu
authors.forename: Kenneth S
authors.initials: KS
authors.lastname: Kendler
authors.forename: Lindon J
authors.initials: LJ
authors.lastname: Eaves
authors.forename: Erik K
authors.initials: EK
authors.lastname: Loken
authors.forename: Nancy L
authors.initials: NL
authors.lastname: Pedersen
authors.forename: Christel M
authors.initials: CM
authors.lastname: Middeldorp
authors.forename: Chandra
authors.initials: C
authors.lastname: Reynolds
authors.forename: Dorret
authors.initials: D
authors.lastname: Boomsma
authors.forename: Paul
authors.initials: P
authors.lastname: Lichtenstein
authors.forename: Judy
authors.initials: J
authors.lastname: Silberg
authors.forename: Charles O
authors.initials: CO
authors.lastname: Gardner
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000704:Analysis of Variance; D001008:Anxiety Disorders / Q000453:epidemiology* / Q000235:genetics / Q000523:psychology; D002648:Child; D003866:Depressive Disorder / Q000453:epidemiology* / Q000235:genetics / Q000523:psychology; D004200:Diseases in Twins / Q000453:epidemiology* / Q000235:genetics / Q000523:psychology; D005060:Europe / Q000453:epidemiology; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007206:Individuality; D008016:Life Change Events; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D012042:Registries / Q000706:statistics & numerical data; D012931:Social Environment; D011795:Surveys and Questionnaires; D014430:Twins, Monozygotic / Q000235:genetics / Q000523:psychology / Q000706:statistics & numerical data; D014481:United States / Q000453:epidemiology; D055815:Young Adult