AMERICAN JOURNAL OF INDUSTRIAL MEDICINE 46:586–598 (2004) Relationship of Work Schedules to Gastrointestinal Diagnoses, Symptoms, and Medication Use in Auto Factory Workers Claire C. Caruso, PhD, RN, 1 Sally L. Lusk, PhD, RN, FAAN, FAAOHN, 2 and Brenda W. Gillespie, PhD 3 Background Gastrointestinal (GI) complaints are common in shift workers. This study examines the relationship between work schedules and GI symptoms, medications, and diagnoses. Methods In a cross-sectional survey of 343 US auto factory workers, four work schedule variables were examined: assigned shift, number of hours worked, number of night hours, and schedule variability. Multiple regression tested the relationship between GI outcomes and work schedule variables while controlling for covariates. Results The evening shift was associated with more GI symptoms and GI diagnoses. Unexpectedly, more consistent work times were associated with having a GI diagnosis. As schedule variability increased the probability of GI medication use increased in low noise exposure. Conclusion Findings suggest that evening shift and widely varying work start and end times may increase risks for GI disturbances. Am. J. Ind. Med. 46:586 – 598, 2004. ß 2004 Wiley-Liss, Inc. KEY WORDS: shift work; overtime; work hours; work schedule; circadian rhythms; sleep; gastrointestinal diseases; digestive system diseases; work schedule tolerance; workload; occupational diseases; occupational exposure INTRODUCTION Shift work is common in industrialized societies. Almost 15% of all American workers work full time on evening, night, rotating, split, or employer-arranged irregular shifts [Bureau of Labor Statistics, 2002]. A negative outcome of these work schedules is the increased risk for health com- plaints and illnesses as well as accidents and errors. Re- searchers theorize that shift work disturbs sleep and circadian rhythms and also causes difficulties in arranging time to spend with family and friends [Barton et al., 1995]. These disturbances, in turn, may lead to increased stress and other health problems. Gastrointestinal (GI) disturbances are one of the most common health complaints reported in shift workers. Vener et al. [1989] theorize that shift work disturbs the timing of GI motility, enzyme availability, and GI acid base balance. GI symptoms could occur theoretically through several mechan- isms: imbalances in the aggressive and defensive factors connected with gastric function which weaken the gastric mucosa barrier [Moore et al., 1994]; imbalances in the inflam- matory cells and anti-inflammatory cells in the intestine [MacDermott, 1996]; sleep disturbances lead to fatigue and ß 2004 Wiley-Liss, Inc. 1 Division of Applied Research and Technology, National Institute for Occupational Safety and Health,Cincinnati, Ohio.Work was performed while at the University of Michigan, School of Nursing. 2 School of Nursing, University of Michigan, Michigan 3 Center for Statistical Consultation and Research, University of Michigan, Michigan Contract grant sponsor: UAW-GM National Joint Committee on Health and Safety. *Correspondence to: Claire C. Caruso, Research Health Scientist, National Institute for Occupational Safety and Health, 4676 Columbia Parkway, MS C-24, Cincinnati, Ohio 45226-1998. E-mail: ccaruso@cdc.gov Accepted 2 September 2004 DOI10.1002/ajim.20099. Published online in Wiley InterScience (www.interscience.wiley.com)