title: Association of overtime work with cellular immune markers among healthy daytime white-collar         employees.
abstract: OBJECTIVE
  Even though overtime work has been suspected to be a risk factor for ill health, little research         has been done to determine the underlying immunological mechanisms. This study investigated the association between         overtime work and cellular immunity among Japanese white-collar workers.
  
  
  METHODS
  A total of 306 healthy, full-time,         non-shift, daytime employees (165 men and 141 women), aged 22-69 (mean 36) years, provided a blood sample for the         measurement of circulating immune [natural killer (NK), B, and T] cells and NK cell cytotoxicity (NKCC) and completed a         questionnaire survey including overtime/month. Blood samples were collected between 09.00-11.00 hours during         working days and participants completed the questionnaire within the two weeks prior to the blood sampling. Stepwise         linear regression analyses controlling for confounders were carried out to examine the relationship between overtime         work and immune markers.
  
  
  RESULTS
  Overtime work was mainly related to short sleep duration, increased weight, and         reduced job satisfaction, and it was more prevalent among men than women and among younger and married employees.         Amount of overtime was inversely associated with NK (CD3-CD56+) cell counts (β=-0.145; P =0.032) but was not         associated with NKCC, NKCC/NK cell ratio, or T or B cells.
  
  
  CONCLUSIONS
  The NK cell is a lymphocyte that possesses         killer activity against tumor and virus-infected cells and constitutes a major component of the innate immune system. A         decrease of NK cell counts from overtime work suggests a dampened innate immune defense. However, the finding needs to         be further validated with a well-designed study using objective overtime measures.
authors.affiliation: Division of Applied Research and Technology, National Institute for Occupational Safety and Health (NIOSH), Cincinnati, OH 45226, USA. cji5@cdc.gov
authors.forename: Akinori
authors.initials: A
authors.lastname: Nakata
authors.forename: Masaya
authors.initials: M
authors.lastname: Takahashi
authors.forename: Masahiro
authors.initials: M
authors.lastname: Irie
mesh_terms: D000328:Adult; D000368:Aged; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007111:Immunity, Cellular; D007564:Japan; D007694:Killer Cells, Natural / Q000276:immunology; D007958:Leukocyte Count; D008297:Male; D008875:Middle Aged; D018448:Models, Immunological; D016272:Occupational Health; D014940:Work Schedule Tolerance / Q000502:physiology*; D016526:Workload; D055815:Young Adult