Shift work and your menstrual cycle

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In a study of more than 71,000 US nurses, researchers found that those working rotating shifts were more likely than other nurses to have irregular menstrual periods.

Irregular, for the purposes of the study, meant that the time between a woman's periods usually varied by more than a week.

Women on rotating shifts were also more likely to have either very short menstrual cycles (fewer than 21 days between periods) or very long ones (40-plus days) - although few women in the study were at either of those extremes.

In general, menstrual irregularities make it harder for a woman to become pregnant. Whether shift work induces disruptions in some women's cycles that contribute to infertility remains unknown for now.

There are also physiological reasons to believe that rotating shifts could alter a woman's menstrual cycle.

Working nights disrupts the body's natural circadian rhythms, and studies have shown that this can alter basic physiological functions - like blood pressure control and hormone production.

"We don't really know the exact mechanism," Lawson said. "One possibility could be that exposure to light at night alters melatonin production."

Melatonin is a hormone produced mainly during dark hours that helps regulate sleep and other body processes. Its relationship to reproductive hormones in humans is not clear.

It's not clear whether that catch-up sleep can right any menstrual irregularities. But it's a wise move for your overall well-being anyway, according to Lawson.

She also suggested that women who work nights pay close attention to their diet and exercise habits - both of which can be challenging for people on irregular work schedules.

Do you work shifts? Have you seen a change in your menstrual cycle?
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