Stability of alexithymia is low from adolescence to young adulthood, and the consistency of alexithymia is associated with symptoms of depression and dissociation

Background: The aims of this study were to investigate the stability of alexithymia from adolescence to young adulthood, as well as the association between alexithymia, peer relationships, and symptoms of depression and dissociation. Methods: The participants (n = 755, aged 13–18 years) were assessed with self-rated questionnaires and the 20-item Toronto Alexithymia Scale (TAS-20) at baseline in 2005 and on follow-up in 2011. Results: The changes in the TAS-20 total score (t = −12.26) and the scores for its subscales, difficulty identifying feelings (DIF) (t = −4.04), difficulty describing feelings (DDF) (t = −5.10), and externally oriented thinking (EOT) (t = −18.23), were statistically significant (p < 0.001). Effect sizes (Cohen's d) for the change indicating absolute stability were small for DIF (−0.15) and DDF (−0.19), medium for TAS-20 total (−0.45), and large for EOT (−0.66) scores. Moderate correlations in test–retests with Spearman's ρ (TAS-20 total 0.46, DIF 0.41, DDF 0.39, EOT 0.43) indicated relative stability, whereas low intraclass correlation coefficients (ICCs) (respectively 0.41, 0.39, 0.37, 0.37) indicated poor reliability of test–retests. In regression analyses, poor relationships with peers, loneliness, and symptoms of depression and dissociation at baseline associated with alexithymia at baseline and on follow-up. Unlike EOT, increases in the TAS-20 total, DIF, and DDF scores during the 6-year follow-up associated with baseline symptoms of depression and dissociation. Conclusions: Alexithymia in adolescence is not always a reliable predictor of alexithymia in young adulthood. Mental health symptoms appear to affect the consistency of alexithymia during adolescent development.