Consistency where it counts: Sleep regularity is associated with circulating white blood cell count in young adults

BACKGROUND: Sleep irregularity is predictive of poor health outcomes, and particularly those of cardiometabolic origins. The immune system is implicated in the pathogenesis of cardiometabolic diseases, however the relation between sleep regularity and immune cell profile is unclear. METHODS AND RESULTS: Forty-two healthy young adults (20 ​± ​2 years) completed 14 days of 24-h wrist actigraphy followed by a morning blood sample to evaluate circulating white blood cells (WBC) and subtypes (neutrophils, lymphocytes, monocytes). Sleep regularity was operationalized as the standard deviation (SD) of nightly sleep duration and SD of sleep onset time. Every 60-min increase in sleep duration SD was associated with an estimated 2.7 ​± ​0.60 x10(3) ​cells/μL (p<0.001) increase in total WBC count, while every 60-min increase in sleep onset SD was associated with an estimated 2.4 ​± ​0.60 x10(3) ​cells/μL (p<0.001) increase in WBCs. Sleep duration SD was also associated with lymphocyte count (11.5 ​± ​3.8 ​cells/μL per 1-min increase, p<0.01), while sleep onset SD was associated with neutrophil (34.7 ​± ​9.8 ​cells/μL per 1-min increase, p<0.01) and monocyte counts (3.0 ​± ​0.9 ​cells/μL per 1-min increase, p<0.01). Sleep regularity metrics remained significantly associated with WBCs in a series of regressions which adjusted for sex, body mass index, resting blood pressure, mean sleep duration, physical activity, dietary sodium, and alcohol consumption. CONCLUSIONS: Unfavorable associations between irregular sleep patterns and circulating immune cells are apparent in young adulthood. These findings contribute to the growing body of evidence suggesting that consistent sleep schedules are an important dimension of sleep and circadian health and may reduce excess chronic disease risk.