Links between objective sleep and sleep variability measures and inflammatory markers in adults with bipolar disorder

Premature mortality and increased physical comorbidity associated with bipolar disorder (BD) may be related to accelerated biological aging. Sleep disturbances and inflammation may be key mechanisms underlying accelerated aging in adults with BD. To our knowledge, these relationships have not been examined rigorously. This cross-sectional study included 50 adults with BD and 73 age- and sex-comparable non-psychiatric comparison (NC) subjects, age 26-65 years. Participants were assessed with wrist-worn actigraphy for total sleep time (TST), percent sleep (PS), and bed/wake times for 7 consecutive nights as well as completing scales for subjective sleep quality. Within-individual variability in sleep measures included intra-individual standard deviation (iSD) and atypicality of one evening's sleep. Blood-based inflammatory biomarkers included interleukin (IL)-6, C-reactive protein (CRP), and tumor necrosis factor-alpha (TNF-α). Linear regression analyses tested relationships of mean and iSD sleep variables with inflammatory marker levels; time-lagged analyses tested the influence of the previous evening's sleep on inflammation. BD participants had worse subjective sleep quality, as well as greater TST iSD and wake time iSD compared to the NC group. In all participants, higher TST iSD and lower mean PS were associated with higher IL-6 levels (p = 0.04, η_p² = 0.042; p = 0.05, η_p² = 0.039, respectively). Lower mean PS was associated with higher CRP levels (p = 0.05, η_p² = 0.039). Atypicality of the previous night's TST predicted next day IL-6 levels (p = 0.05, η_p² = 0.04). All of these relationships were present in both BD and NC groups and remained significant even after controlling for sleep medications. Overall, sleep measures and their variability may influence inflammatory markers in all adults. Thus, sleep may be linked to the inflammatory processes believed to underlie accelerated aging in BD.