The later, the better: evening chronotypes in Uruguayan shift workers are associated with longer sleep in an observational study

Shift work disrupts sleep patterns and is associated with adverse health outcomes, yet the role of chronotype in shaping shift workers’ sleep behavior remains underexplored. We conducted a field study of 85 shift workers at an industrial plant in Uruguay operating under a slow, counterclockwise three-shift rotation system. We assessed sleep timing, duration, napping, and chronotype using an abbreviated Munich Chronotype Questionnaire for shift workers. Night and morning shifts produced the largest shifts in sleep timing and the greatest restriction in sleep duration. Workday sleep was shorter, and napping was more frequent, during morning and night shifts than during the afternoon shift and days off. Participants were predominantly evening-oriented. Chronotype strongly modulated sleep patterns: evening-oriented workers slept longer during night and afternoon shifts and days off, and napped longer on morning workdays. A 1-hour delay in chronotype was associated with 6–25 min of additional sleep. Weekly average 24-hour sleep duration remained below recommended levels during morning and night shifts (~ 7 h) but exceeded 8 h during the afternoon shift, with longer sleep among later chronotypes. These findings identify chronotype as a key factor shaping sleep under shift work and support its consideration in shift scheduling to improve sleep health and reduce the adverse effects of shift work.