Nightshift work and irregular menstrual cycle: 8-year follow-up cohort study

Area of Science:

• Occupational Health
• Reproductive Endocrinology
• Epidemiology

Background:

• Irregular menstruation is a significant health concern for women.
• The link between nightshift work and menstrual irregularities is not well-established.
• Previous research has yielded controversial findings regarding this association.

Purpose of the Study:

• To investigate the association between nightshift work and irregular menstrual cycles in female workers.
• To explore potential moderating effects of sleep quality, working hours, and obesity on this relationship.

Main Methods:

• Cross-sectional and longitudinal study design involving female workers (N=87,147 and N=41,516, respectively).
• Data collected via self-administered questionnaires on nightshift work, working hours, sleep quality, and menstrual cycle characteristics.
• Irregular menstruation defined as self-reported irregularity or cycle length ≥36 days.
• Statistical analyses included multivariable logistic regression and Cox proportional hazard models.

Main Results:

• Nightshift work was significantly associated with prevalent irregular menstrual cycles (OR=1.26, 95% CI 1.2-1.33).
• Nightshift work was also linked to incident irregular menstrual cycles over 6 years (aHR=1.95, 95% CI 1.61-2.35).
• No significant interactions were found when stratifying by sleep quality, working hours, or obesity.

Conclusions:

• Nightshift work is independently associated with an increased risk of both prevalent and incident irregular menstrual cycles.
• The observed association is robust and not significantly modified by sleep quality, working hours, or obesity.
• Findings highlight the importance of considering occupational exposures in reproductive health.