Shift work with and without night work as a risk factor for fatigue and changes in sleep length: A cohort study with linkage to records on daily working hours

We examined shift work with or without night work as a risk factor for fatigue and short or long sleep. In a prospective cohort study with 4- and 6-year follow-ups (the Finnish Public Sector study), we linked survey responses of 3,679 full-time hospital employees on sleep duration and fatigue to records on daily working hours in 2008 (baseline), 2012 and 2014. We used logistic regression to estimate risk ratios and their confidence intervals to examine whether continuous exposure to shift work or changes between shift work and day work were associated with short (<= 6.5hr) or long (>= 9.0hr) sleep over 24hr and fatigue at work and during free days. Compared with continuous day work and adjusting for age, gender, education and fatigue/sleep duration at baseline, continuous shift work with night shifts was associated with increased fatigue during free days (risk ratio=1.38, 95% confidence interval 1.17-1.63) and long sleep (risk ratio=8.04, 95% confidence interval 2.88-22.5, without adjustment for education) after 6-year follow-up. Exposure to shift work without night shifts increased only long sleep after 6years (risk ratio=5.87, 95% confidence interval 1.94-17.8). A change from day work to shift work with or without night shifts was associated with an increased risk for long sleep, and a change from shift work to day work with a decreased risk for long sleep and fatigue. This study suggests that irregular shift work is a modifiable risk factor for long sleep and increased fatigue, probably reflecting a higher need for recovery.