title: The impact of shift work induced chronic circadian disruption on IL-6 and TNF-alpha immune responses.
abstract: OBJECTIVE
  Sleep disturbances induce proinflammatory immune responses, which might increase cardiovascular disease risk. So far the effects of acute sleep deprivation and chronic sleep illnesses on the immune system have been investigated. The particular impact of shift work induced chronic circadian disruption on specific immune responses has not been addressed so far.
  
  
  METHODS
  Pittsburgh-Sleep-Quality-Index (PSQI) questionnaire and blood sampling was performed by 225 shift workers and 137 daytime workers. As possible markers the proinflammatory cytokines IL-6 and TNF-alpha and lymphocyte cell count were investigated. A medical examination was performed and biometrical data including age, gender, height, weight, waist and hip circumference and smoking habits were collected by a structured interview.
  
  
  RESULTS
  Shift workers had a significantly higher mean PSQI score than day workers (6.73 vs. 4.66; p < 0.001). Day workers and shift workers had similar serum levels of IL-6 (2.30 vs. 2.67 resp.; p = 0.276), TNF-alpha (5.58 vs. 5.68, resp.; p = 0.841) or lymphocytes count (33.68 vs. 32.99, resp.; p = 0.404). Furthermore there were no differences in cytokine levels (IL-6 p = 0.761; TNF-alpha p = 0.759) or lymphocyte count (p = 0.593) comparing the sleep quality within the cohorts. When this calculation of sleep quality was stratified by shift and day workers irrespective of their sleep quality day workers and shift workers had similar serum levels of IL-6, TNF-alpha or lymphocytes count. Multiple linear regression analysis showed a significant correlation of lymphocytes count and smoking habits.
  
  
  CONCLUSIONS
  Shift work induces chronic sleep debt. Our data reveals that chronic sleep debt might not always lead to an activation of the immune system, as we did not observe differences in lymphocyte count or level of IL-6 or TNF-alpha serum concentration between shift workers and day workers. Therefore chronic sleep restriction might be eased by a long-term compensating immune regulation which (in healthy) protects against an overstimulation of proinflammatory immune mechanisms and moderates metabolic changes, as they are known from short-term sleep deprivation or sleep related breathing disorders.
authors.affiliation: Institute of Occupational Medicine, University of Lübeck, 23538 Lübeck, Ratzeburger Allee 160, Germany. anke.van.mark@arbeitsmedizin.uni-luebeck.de.
authors.forename: Anke
authors.initials: A
authors.lastname: van Mark
authors.forename: Stephan W
authors.initials: SW
authors.lastname: Weiler
authors.forename: Marcel
authors.initials: M
authors.lastname: Schröder
authors.forename: Andreas
authors.initials: A
authors.lastname: Otto
authors.forename: Kamila
authors.initials: K
authors.lastname: Jauch-Chara
authors.forename: David A
authors.initials: DA
authors.lastname: Groneberg
authors.forename: Michael
authors.initials: M
authors.lastname: Spallek
authors.forename: Richard
authors.initials: R
authors.lastname: Kessel
authors.forename: Barbara
authors.initials: B
authors.lastname: Kalsdorf