A new study led by York University’s Faculty of Health researchers investigates how the onset of menopause may be affected by shift work.
Working for eight hours from 9 a.m. to 5 p.m. on weekdays is considered a regular daytime job, and the term “shift work” is defined as any work outside these regular daytime hours. Living in a globalized 24-hour society with the consumption of services, products, and entertainment happening around the clock has led to an increase in shift work. A wide range of negative health outcomes – such as previously studied vascular events, gastrointestinal disorders and diabetes for example – have been associated with shift work, in particular, night shifts and rotating shifts; however, little is known about the effects of shift work exposure on reproductive health outcomes.
Researchers in the Faculty of Health prospectively investigated the association between shift work exposure and the variations in age at natural menopause among adult Canadian workers.
Published in Menopause, the journal of the North American Menopause Society, the study “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)” considered more than 3,500 pre-menopausal women and their experience with shift work.
The study’s lead author is Durdana Khan, a fourth-year PhD candidate in the School of Kinesiology and Health Science (epidemiology), who worked with York Professors Michael Rotondi, Heather Edgell and Hala Tamim to conduct the research.
“The study involved 3,688 pre-menopausal women included in the Canadian Longitudinal Study on Aging database, a nationwide cohort study of adults aged 45 to 85. The women were asked whether they had ever been exposed to shift work and whether their current or longest job work schedule was daytime work, night shift or rotating shifts,” said Khan. “We found that, overall, one out of five women (20 per cent) reported to be ever exposed to shift work during their jobs.”
Specifically, 3.6 per cent and 8.1 per cent of the currently working women reported to be exposed to night and rotating shift work respectively. Considering the job held the longest in their entire career, 4.7 per cent and 13.1 per cent of the women reported being exposed to night and rotating shift work respectively.
Researchers found that exposure to shift work was associated with later onset of menopause. Particularly, women who worked as a rotating shift worker in the current job or in the longest job experienced delayed onset of menopause.
Age at natural menopause is a matter of concern for middle-aged and older women, as both early or late menopause may be a significant risk marker for subsequent morbidity and mortality. While the exact underlying mechanisms aren't known, rotating shift work has been hypothesized to be more disruptive to the circadian rhythm than regular night work and has been studied previously as a risk factor for adverse reproduction-related outcomes, says Khan.
"Our study is one of the first Canadian studies to prospectively investigate the associations between shift work and age at natural menopause among a diverse group of Canadian workers, using a large population-based sample," said Khan. "Investigating and identifying the modifiable factors of age at natural menopause, like shift work exposure among working populations, is of clinical relevance given the potential adverse health outcomes associated with variations in menopausal timing. These preliminary study results would add insight on the impact of shift work on reproductive function and further elucidate the role of circadian regulation on timing of natural menopause."
Although the study’s findings do not offer conclusive evidence, it does suggest that rotating shift work exposure may contribute to a delaying effect of age at natural menopause, said Khan. “This delaying effect of rotating shift work on age at natural menopause has not been reported before, therefore, to develop a complete picture of the relationship between shift work and onset of menopause, additional studies will be needed to confirm the association and to determine any physiological pathways that are influenced. Future studies should examine further details of shift work and how they relate to age at menopause, such as the type and direction of rotation shift, the number of consecutive night shifts and the number of days off between shifts.”
Khan was the recipient of the Lillian Meighen Wright Foundation Maternal Child Health Scholarship for graduate studies at York University (2019). She is a doctoral trainee at the LaMarsh Centre for Child & Youth Research. She was awarded a U.S. Fullbright Scholarship for master's of public health study at the Ohio State University (2010-12).
Learn more by watching a video summary of the research.