Previous studies have linked shift work, work outside of typical daytime hours, to health problems like cardiovascular disease and reproductive issues. A recent Canadian study published in Menopause found shift work may also influence when a woman starts menopause.
Data were pulled from nearly 4000 premenopausal Canadian women included in the Longitudinal Study on Aging database. Of these women surveyed, around 20% did shift work at some point in their lives.
After a 3-year follow-up and adjusting for confounders, shift work was found to affect menopause onset. Interestingly, women who worked night shifts went through menopause earlier, at an average age of 53 years old. Women who had rotating shift work, or shifts at different times of the day and night, started menopause at a later average age, at 55 years old. This latter finding has not been previously reported, according to the study's researchers.
One of the study's authors, Durdana Khan, MPH, reported that these effects of shift work on menopause are clinically relevant because menopause timing can be associated with potential adverse health outcomes.
Shift work is thought to affect menopause onset by interfering with circadian rhythms. According to Khan and colleagues, rotating shift work is hypothesized to be more disruptive to the circadian rhythm than regular night work since the irregular schedule of rotating shift work makes it more difficult for a worker to adapt. This may be, more specifically, related to how circadian disruption affects estrogen production.
Not considering shift work, higher estrogen levels in general, like those produced in women who are obese, are linked to delayed menopause. In women who smoke, who often undergo menopause at an earlier age, lower estrogen levels from polycyclic aromatic hydrocarbons in cigarette smoke are thought to be the reason.