Objective and Subjective Intraindividual Variability in Sleep: Predisposing Factors and Health Consequences.

OBJECTIVE: We investigated the factors that predispose or precipitate greater intra-individual variability (IIV) in sleep. We further examined the potential consequences of IIV to overall sleep quality and health outcomes, including whether these relationships were found in both self-reported and actigraphy-measured sleep IIV.

METHODS: In Study 1, 699 US adults completed a Sleep Intra-Individual Variability questionnaire and self-reported psychosocial, sleep quality, and health outcomes. In Study 2, 100 university students wore actigraphy and completed psychosocial, sleep, and health surveys at multiple timepoints.

RESULTS: In cross-sectional analyses that controlled for mean sleep duration, predisposing/precipitating factors to greater IIV were being an under-represented racial/ethnic minority (Study 1: F = 13.95, p < .001; Study 2: F = 7.03, p = .009), having greater stress (Study 2: r values ≥ 0.32, p values ≤ 0.002) or trait vulnerability to stress (Study 1: rs ≥ 0.15, ps < 0.001), and showing poorer time management (Study 1: r = -0.23, p < 0.001; Study 2: rs ≤ -0.26, ps ≤ 0.013). In addition, both studies showed that greater sleep IIV was associated with decreased overall sleep quality, independent of mean sleep duration (Study 1: rs ≥ 0.20, ps < 0.001; Study 2: rs ≥ 0.33, ps ≤ 0.001). Concordance across subjective and objective IIV measures was modest (rs: 0.09-0.35) and similar to concordance observed for subjective-objective mean sleep duration measures.

CONCLUSION: Risk for irregular sleep patterns is increased in specific demographic groups and may be precipitated by, or contribute to, higher stress and time management inefficiencies. Irregular sleep may lead to poor sleep quality and adverse health outcomes, independent of mean sleep duration, underscoring the importance of addressing sleep consistency.