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Sleeping in on weekends may cause period pain by disrupting normal reproductive cycles, a study in female university students suggests.

We already know that female shift-workers are more prone to irregular menstrual cycles, difficulties falling pregnant and miscarriages, possibly because their irregular schedules affect the circadian rhythms that control their hormone cycles.

Yoko Komada at Meiji Pharmaceutical University in Japan and her colleagues wondered if social jetlag – a pattern of sleeping in on weekends to make up for early starts during the week – may have similar effects.

To find out, they surveyed…