Estradiol levels in relation to chronotype and sleep loss in women

During puberty, both sexes experience a well-documented shift toward eveningness, suggesting that physiological changes during this developmental stage drive this transition. Sex hormones have been proposed as a key factor in this shift, a hypothesis that has been corroborated in men—several studies using different methodologies have confirmed that higher testosterone levels are linked to eveningness in males. However, research examining a similar phenomenon in women—specifically, the relationship between major female sex hormones and chronotype—remains limited. In this pre-registered study, with hypotheses formulated prior to data collection, we expected that in females, eveningness would be associated with higher estradiol levels. We used an observational, between-subjects design with a sample (N = 186) of naturally cycling young women who were free of hormonal medications, contraceptive use, and endocrine disorders. Participants self-reported their chronotype and morningness-eveningness, and their hormone levels were assessed from blood samples collected during the early follicular phase. Results showed no association between estradiol levels and chronotype or morningness-eveningness. However, lower estradiol levels were observed in individuals experiencing greater sleep loss throughout the weekdays. These findings suggest that estradiol does not influence habitual sleep timing but may be diminished by insufficient sleep.