A Canadian study published in the journal Menopause found a significant link between rotating shift work and delayed onset of menopause.
“Shift work is dominant throughout the world,” said principal investigator Durdana Khan, MPH, a fourth-year doctoral candidate in kinesiology and health sciences at York University in Toronto, Canada. “Consistent with the literature, our study found that one in every five Canadians is exposed to shift work.”
The global aging phenomenon—coupled with the increasing share of women in the workforce—sparked Khan’s interest in the potential impact of occupational factors on women’s health.
The study is a secondary data analyses of the Canadian Longitudinal Study on Aging which followed 3688 premenopausal women prospectively for 3 years from 2015 to 2018.
Overall, 3.6% and 8.1% of the currently working women reported night and rotating shift work, respectively. The job held longest in their careers involved night and rotating shift work, respectively, among 4.7% and 13.1% of women.
Those exposed to shift work were significantly associated with a delayed onset of menopause compared to daytime workers: hazard ratios (HR) = 0.77; 95% confidence interval (CI): 0.61 to 0.98.
Notably, compared to daytime workers, rotating shift workers in the current and longest job were significantly connected to delayed onset of menopause: HR = 0.64; 95% CI: 0.46 to 0.89, and HR = 0.65; 95% CI: 0.49 to 0.86, respectively.
“Starting menopause late has been associated with a higher risk of some cancers, including breast,” Khan told Contemporary OB/GYN®. “While the exact underlying mechanisms are not known, rotating shift work is hypothesized to be more disruptive to the circadian rhythm than regular night work,” she said. “Rotating shift work has also been previously studied as a risk factor for adverse reproduction-related outcomes.”
Khan noted that the delaying effect of rotating shift work on menopause timing in the current study might be the result of circadian disruption on estrogen production. “Previous studies have shown that impaired pineal secretion of melatonin—due to light exposures among shift workers—may cause increased release of estrogen by the ovaries, which is an indicator of delayed menopause,” she said.
Additional studies are needed to confirm the link between shift work and onset of menopause and to determine if any physiological pathways are influenced, Khan said.
“Meanwhile, we live in a globalized 24-hour society that consumes services, products and entertainment around the clock,” she said. “Shift work may be a social and economic necessity, but its negative impact on workers’ health cannot be overlooked.”
Despite the growing number of female shift workers and reproductive health issues related to menopause, “it might be hard to completely avoid shift work exposure from our society because we require shift work in very important industries like healthcare and security,” Khan said. “But we all can lessen the impact of circadian disruption by trying to lead a healthy life and maintaining a work-life balance.”
Khan also advocates further studies that focus on important aspects of shift work, such as the type of rotating shifts, number of consecutive night shifts worked, and the number of days off between shifts.
“Incorporating reproductive factors like breastfeeding and menarche into shift work would also be valuable,” she said.
Khan D, Rotondi M, Edgell H, et al. The association between shift work exposure and the variations in age at natural menopause among adult Canadian workers: results from the Canadian Longitudinal Study on Aging (CLSA). Menopause. Published online March 25, 2022. doi:10.1097/GME.0000000000001981