Sleep complaints in alexithymia reflect non-specific negative affectivity

Alexithymia is the inability to identify and describe emotions, associated with an increased risk of somatic and psychiatric disease. Alexithymia is also characterized by reduced subjective sleep quality. However, it is not well-known if this reduction in sleep quality reflects physiological changes in sleep, a specific alteration in perceived sleep quality not captured by objective metrics, or a non-specific spillover of the negative affective style which characterizes alexithymia. In BSETS, a large (N = 228) in-home EEG study of naturalistic sleep, we found that alexithymia symptoms are associated with worse habitual (AIS) and current (GSQS) subjective sleep quality (β_AIS = 0.207, p_AIS = 0.002, β_GSQS = 0.203, p_GSQS = 0.002). However, we observed no significant association between alexithymia and EEG-based sleep efficiency (β = -0.017, p = 0.791). The association with subjective sleep quality was almost completely attenuated when controlling for either depressive symptoms (PHQ-9, β_AIS = 0.001, p_AIS = 0.982, β_GSQS = 0.044, p_GSQS = 0.486) or trait neuroticism (ZKPQ, BFI-44, β_AIS = 0.057, p_AIS = 0.442, β_GSQS = 0.048, p_GSQS = 0.514). A possible exception is the Difficulty Identifying Feelings alexithymia dimension, reflecting complaints about the labeling of interoceptive experiences, which was associated with lower subjective sleep quality even after covariate control. This pattern of findings suggests that alexithymia is characterized only by alterations of subjective sleep quality, and even these reflect a non-specific increase in negative affect which influences self-reports of sleep quality, rather than a specific reduction in perceived sleep quality itself.