Gender differences in the association between objective sleep quality and leukocyte count: The HEIJO-KYO cohort

Chronic low-grade systemic inflammation increases cardiovascular risk and mortality. Subjective assessment of sleep quality in previous observational studies has demonstrated associations with biomarkers of systemic inflammation, although the results are conflicting. In this cross-sectional study on 1098 elderly individuals, circulating white blood cell (WBC) count and actigraphic sleep quality were measured as indices of systemic inflammation and objective sleep quality, respectively. Lower sleep efficiency (SE) and longer wake after sleep onset (WASO) were significantly associated with increased WBC count in females (n=581) but no significant associations were observed in the association between WBC count and all objective sleep parameters in males (n=517). The associations of lower SE and longer WASO with increased WBC count in females remained significant in multivariable models adjusted for potential confounding factors. These results indicated that a 1-standard deviation increase in SE (8.0%) and WASO (27.7min) corresponded to a 0.16×10(9)/L (95% confidence interval: 0.05 to 0.27×10(9)/L) decrease and 0.14×10(9)/L (95% confidence interval: 0.03 to 0.25×10(9)/L) increase in circulating WBC count, respectively. In contrast, total sleep time and sleep onset latency were not significantly associated with WBC count in multivariable models. In conclusion, decrease in objectively measured sleep quality was significantly associated with increased circulating WBC count in females but not males, independently of known factors related to systemic inflammation including age, obesity, smoking, hypertension, diabetes, and physical inactivity.