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Manuel Spitschan: The Menstrual Cycle is Biology, Not Noise

Manuel Spitschan/researchgate.net

Aug 23, 2026, 15:22

Manuel Spitschan: The Menstrual Cycle is Biology, Not Noise

Manuel Spitschan, Academic Program Director (APD) for Health Science at the Technical University of Munich, shared on LinkedIn:

” ‘The menstrual cycle is biology, not noise.’

Yesterday at the Swiss Society for Sleep Research, Sleep Medicine and Chronobiology (SSSSC) meeting in Zürich, I gave a talk titled ‘Sex as a biological variable in circadian and neuroendocrine responses to light’.

The four main messages from my talk were:

Sex matters for circadian and neuroendocrine responses to light, yet the evidence base remains substantially sex-biased, with female participants historically underrepresented or excluded.
Differences begin with exposure itself. Female participants may receive systematically different amounts and timing of light, including substantially lower morning light exposure.
Female physiology should be studied, not controlled away. Menstrual-cycle and hormonal variation are biologically meaningful dimensions that may reveal mechanisms of light sensitivity.
Better evidence requires better study design, including balanced recruitment, explicit sex-stratified analyses, appropriate measurement of hormonal state, preregistration, and Registered Reports.

Thank you to the organizers and co-speakers – Esther Irene Schwarz, Sarah Schoch and Christian Cajochen – and everyone at SSSSC for the thoughtful discussion. And a huge thanks to my co-chair Daniela Noain!”

Manuel Spitschan: The Menstrual Cycle is Biology, Not Noise