Nurses provide care around the clock in a three-shift system (daytime nighttime late night) consisting of
three 8 h shifts within 24 hours, or in a two-shift system with an 8 h day shift and a 16 h night shift. In contrast
with the three-shift system, the benefit of the two-shift system is in ensuring the safety of nurses by having them
leave work before midnight, as well as reassuring the patients by providing continuity of care by the same nursing
staff. Nevertheless, the long 16 h shift is apt to cause physical and mental exhaustion and disrupt the normal
circadian rhythm [1]. Furthermore, many reports have confirmed that prolonged night schedule is highly stressful
[2] [3] and associated with higher burnout rates [4] [5] and medical errors, but the precise physiological effects
of a 16 h shift remain undetermined. Most assessments of fatigue rely on questionnaires that evaluate subjective
fatigue severity while practical, objective evaluations are virtually nonexistent. In this study, we collected
salivary samples as a simple and minimally invasive method of biochemically evaluating fatigue and stress [6]
[7]. The aim of this study was to objectively measure fatigue and stress via salivary assays and determine the correlation
between stress and fatigue and prolonged night shifts in order to generate data that would be informative for
improving the work hours and well-being of nurses.