Time worked in shifts and occurrence of drowsiness events while driving: attenuating effect of physical activity

Shift work disrupts circadian rhythms and is associated with adverse sleep outcomes, such as daytime sleepiness and drowsiness while driving. This study aimed to investigate the relationship between history of shift work, drowsiness events during driving, and the potential moderating effect of physical activity.

A cross-sectional investigation involved 1,413 male shift workers in an iron ore mining firm. Heavy machinery essential to the mining process was operated. A specific question from the Berlin Questionnaire was used to evaluate drowsiness while driving, asking whether participants had ever felt drowsy or fallen asleep while driving, regardless of whether the episode occurred during work-related or leisure-time driving. The main explanatory variable was the shift in working hours. The levels of physical activity were classified as low, moderate, and high using the IPAQ. Multivariate and descriptive logistic regression analyses were conducted.

The majority of workers were aged 20 to 34 (45.1%), self-identified as non-white (77.2%), and had completed high school (76.0%). The average history of shift work time was 9.56 years (95% CI: 9.23-9.90), with 76% working for five years or more. Drowsiness events while driving were reported by 17.3% of workers. Multivariate analysis showed a significant association between history of shift work and drowsiness events, indicating a dose-response relationship, where longer history of shift work time increased the likelihood of drowsiness events (OR: 2.93 for 10-15 years; OR: 4.34 for > 15 years). However, physical activity acted as a moderating factor, demonstrating a dose-response effect in reducing this chance, with a reduction of 27.6% and 30.9% for moderate and high levels, respectively, compared to participants with a low level of activity.

A longer history of shift work time increases the chance of drowsiness events during driving, but higher physical activity levels mitigate them.