A wide range of negative health outcomes have been associated with shift work (SW) particularly night and rotating SW. However, little is known about effects of SW exposure on reproductive health outcomes. The objective of our study is to prospectively investigate the association between SW exposure and the variations in age at natural menopause among adult Canadian workers.
Secondary data analyses were performed using the Canadian Longitudinal Study on Aging database. Premenopausal women (N = 3,688) at baseline were followed prospectively for 3 years. Three derived variables were used to measure SW primary exposure: 1) ever exposed to SW, 2) SW exposure in current job, and 3) SW exposure in the longest job. Cox proportional hazard regression models were used to evaluate risk of variations in age at natural menopause after adjusting for potential confounders.
One out of five women (20%) reported to be ever exposed to SW during their jobs. Overall, women who were ever exposed to SW were significantly associated with a delayed onset of menopause compared with daytime workers (hazard ratios [HR] = 0.77, 95% CI, 0.61-0.98). Particularly, when compared with daytime workers, rotating shift worker in the current and longest job were significantly related to delayed onset of menopause (HR = 0.64, 95% CI, 0.46-0.89 and HR = 0.65, 95% CI, 0.49-0.86), respectively.
Our results suggest a relationship between rotating shift and delayed onset of menopause. We speculate that disruptive circadian stimuli may play a role in menopausal onset and this warrants further investigation.