The load on shift work seems to affect the timing of menopause in two directions, new data suggest.
Among nearly 4,000 Canadian women surveyed, one in five reported shift work – that is, outside of normal daytime working hours – at some point in their lives. After adjusting for confounders, rotating shift workers had a later average age of menopause while night shift workers began an earlier menopause.
“The study and identification of the modifying factors of the age of natural menopause such as shift workload among work populations is of clinical relevance due to the potential adverse health outcomes associated with variations in menopausal timing,” Durdana Khan, MPH, and colleagues write in their article. published in Menopause.
This delaying effect of rotating shift work on age during natural menopause has not been previously reported, the researchers note
The results, while preliminary, “add insights into the impact of shift work on reproductive function and further elucidate the role of circadian regulation on timing of natural menopause,” Khan of the School of Kinesiology and Health Science, York University, Toronto, Ontario, Canada, and coauthors add.
“Whether these age-related menopausal differences are directly related to the effect of circadian rhythm changes on subterranean hypothalamic regulation or whether they are due to other sociodemographic factors such as chronic stress, economic insecurity, and substance abuse or substance abuse requires further study,” the study noted. of the North American Menopause Society Stephanie Faubion, MD, in a statement.
Shift work associated with altered menopause timing
The study involved 3688 premenopausal women included in the Canadian longitudinal study on Aging Database, a national cohort study of adults aged 45-85 years. They were asked if their current or longest work schedule was daytime, night shift, or rotating shifts, and whether they had ever been exposed to shift work.
In total, 20% reported some exposure to shift work during their current or previous job. Specifically, 3.6% reported load for night shift work and 8.1% for rotating shift work. For their longest held jobs, 4.7% reported night shift work and 13.1% rotating shift work.
Over 3 years of follow-up and after adjustment for confounders, those who had ever been exposed to shift work – night or rotating – had a significantly later average mean age of natural menopause compared to current day laborers (median age 55 vs 54 years; hazard ratio [HR]0.77).
Among those currently working, night shift workers had a significantly earlier average age at menopause (53 years) compared with day workers (54 years; HR, 1.27), while rotary shift workers had a later age of menopause (55 years; HR, 0.64).
Age at natural menopause is a concern for middle-aged and elderly women, as early or late menopause can be a significant risk marker for subsequent morbidity and mortality.
While the exact subterranean mechanisms are not known, rotational shift work has been hypothesized to be more disturbing to the circadian rhythm than normal night work and has been previously studied as a risk factor for adverse reproductive outcomes, Khan and colleagues point out.
“It is possible that rotating shift workers find it more difficult to adapt to work schedules because they have to move from layer to layer compared to normal night shift workers.”
“In addition, the delaying effect of rotational shift work may be at the age of natural menopause in our study due to effects of circadian disturbance on estrogen production,” they say.
Sociodemographic factors also associated with early and late menopause
Later natural menopause was also seen among workers with overweight (HR, 0.76), obesity (HR, 0.77) and high parity (HR, 0.83), whereas earlier menopause was more likely in those who were currently smokers (HR, 0.73). HR, 1.49) and those who engaged in regular physical activity (HR, 1.21).
The association with obesity may relate to an increased estrogen production in the adipose tissue of obese women, say Khan and colleagues.
As for the smoking compound, “polycyclic aromatic hydrocarbons in cigarette smoke have detrimental effects on the growth of ovarian follicles, thereby reducing circulating estrogen and accelerating the onset of menopause.”
The association with employment and income levels could be mediated through social and psychological stress, which can affect ovarian function and natural menopause timing, they also note.
“Although our findings do not provide conclusive evidence, they suggest that a delaying effect of rotating shift work exposure in old age and natural menopause may be plausible,” they conclude.
Funding for the Canadian Longitudinal Study on Aging has been provided by the Government of Canada through the Canadian Institutes of Health Research and the Canada Foundation for Innovation. Khan has no further publications.
Menopause. Published March 21, 2022.
Miriam E. Tucker is a freelance journalist based in the Washington, DC, area. She is a regular contributor to Medscape, with other works appearing in the Washington Post, NPR Shots Blog, and Diabetes Forecast Magazine. She’s on Twitter: @MiriamETucker.
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