Impact of shift starting time on sleep duration, sleep quality, and alertness prior to injury in the People's Republic of China

Early shift start time and night shifts are associated with reduced sleep duration and poor sleep quality that often lead to adverse safety and health outcomes.  This study investigates the impact of shift starting time on sleep patterns, and alertness / sleepiness at the time of injury, in a large epidemiological field study of hospitalized adults with severe work-related hand injury in the People’s Republic of China (PRC) recruited from 11 hospitals in the PRC.  ANCOVA was used to compare sleep duration, sleep quality, and alertness/sleepiness across 3h increments of shift start time adjusting for age, gender, work hours, shift duration, day of injury. Effect modification by gender was evaluated. 703 adults completed a face-to-face interview within 4 days of injury; 527 (75.0%) were male, with a mean (±SEM) age of 31.8±0.4 years working long weekly (55.7±0.6h) and daily hours (8.6±0.07h). Average sleep duration prior to injury was 8.5h (±0.07), showing significant variations (p-value <0.05) across shift starting time increments. Mean prior sleep duration was shortest for individuals starting shifts from “21:00-23:59” (5.6±0.8h) followed by “00:00-02:59” (6.1±0.6h).  A statistically significant interaction (p<0.05) was observed between gender and shift starting time, for males shortest sleep duration was 5.6h (“21:00-23:59”) and females shortest was 4.3h (“24:00-02:59” and “1500-17:59”). Sleep quality and alertness/sleepiness (KSS) did not vary significantly across shift starting time.  Chinese sleep longer thanl US day workers (Sleep in America Poll, 2012, 6:44 workdays, 7:35 free days) which may help to explain higher than expected alertness / sleepiness scores.