Sleep continuity and stress physiology are associated with non-inflammatory variation in lymphocyte counts.

Sleep disruption and psychological stress influence immune dynamics, but the cross-sectional immune correlates of this interaction in healthy adults remain unclear. We investigated whether sleep disturbance and stress were associated with variation in lymphocyte counts in the absence of overt inflammation. The study was performed using data from the São Paulo Epidemiological Sleep Study (EPISONO). All participants included had undergone full-night polysomnography and completed validated sleep and fatigue questionnaires. Lymphocyte counts, bedtime salivary cortisol, plasma interleukin-6 (IL-6), interleukin-10 (IL-10), and tumor necrosis factor alpha (TNF-α) were quantified. Lymphocyte counts were examined continuously and across physiologically defined strata. Lower sleep efficiency, longer sleep latency, and greater insomnia severity were each associated with higher lymphocyte counts. N1 was the sleep-stage parameter most consistently associated with lymphocyte variation. Elevated bedtime salivary cortisol concentrations were associated with lower sleep efficiency but not with lymphocyte counts, whereas IL-6, IL-10, and TNF-α did not show a consistent association with lymphocyte variation. Fatigue ratings showed a weaker pattern, with participants reporting general fatigue exhibiting the highest lymphocyte counts. These findings suggest that subtle reductions in sleep continuity are associated with mild, non-inflammatory increases in lymphocyte counts, supporting a physiological association between sleep-stress physiology and circulating lymphocyte variation in otherwise healthy adults.