It has an effect, period Global study finds menstrual cycles are a key driver of women’s moods. Credit: MHJ / Getty Images A huge, multi-country analysis of menstrual cycles has revealed their strong influence on individual mood, behaviour and vital signs. A research team led by Emma Pierson from Stanford University and Microsoft Research New England, US, found that the menstrual cycle had a greater effect on fluctuating mood, behaviours and vital signs compared to daily, weekly and seasonal cycles. The team’s study, published today in the journal Nature, is built on a substantial dataset of 241 million observations from 3.3 million women across 109 countries, including Australia and New Zealand. The data were sourced from a women’s health mobile app named Clue, launched in 2013 by European technology company Biowink GmbH. Data recording was consensual and anonymous.